[ShrinkWrap] Add (a simplified version) of shrink-wrapping.

This patch introduces a new pass that computes the safe point to insert the
prologue and epilogue of the function.
The interest is to find safe points that are cheaper than the entry and exits
blocks.

As an example and to avoid regressions to be introduce, this patch also
implements the required bits to enable the shrink-wrapping pass for AArch64.


** Context **

Currently we insert the prologue and epilogue of the method/function in the
entry and exits blocks. Although this is correct, we can do a better job when
those are not immediately required and insert them at less frequently executed
places.
The job of the shrink-wrapping pass is to identify such places.


** Motivating example **

Let us consider the following function that perform a call only in one branch of
a if:
define i32 @f(i32 %a, i32 %b)  {
 %tmp = alloca i32, align 4
 %tmp2 = icmp slt i32 %a, %b
 br i1 %tmp2, label %true, label %false

true:
 store i32 %a, i32* %tmp, align 4
 %tmp4 = call i32 @doSomething(i32 0, i32* %tmp)
 br label %false

false:
 %tmp.0 = phi i32 [ %tmp4, %true ], [ %a, %0 ]
 ret i32 %tmp.0
}

On AArch64 this code generates (removing the cfi directives to ease
readabilities):
_f:                                     ; @f
; BB#0:
  stp x29, x30, [sp, #-16]!
  mov  x29, sp
  sub sp, sp, #16             ; =16
  cmp  w0, w1
  b.ge  LBB0_2
; BB#1:                                 ; %true
  stur  w0, [x29, #-4]
  sub x1, x29, #4             ; =4
  mov  w0, wzr
  bl  _doSomething
LBB0_2:                                 ; %false
  mov  sp, x29
  ldp x29, x30, [sp], #16
  ret

With shrink-wrapping we could generate:
_f:                                     ; @f
; BB#0:
  cmp  w0, w1
  b.ge  LBB0_2
; BB#1:                                 ; %true
  stp x29, x30, [sp, #-16]!
  mov  x29, sp
  sub sp, sp, #16             ; =16
  stur  w0, [x29, #-4]
  sub x1, x29, #4             ; =4
  mov  w0, wzr
  bl  _doSomething
  add sp, x29, #16            ; =16
  ldp x29, x30, [sp], #16
LBB0_2:                                 ; %false
  ret

Therefore, we would pay the overhead of setting up/destroying the frame only if
we actually do the call.


** Proposed Solution **

This patch introduces a new machine pass that perform the shrink-wrapping
analysis (See the comments at the beginning of ShrinkWrap.cpp for more details).
It then stores the safe save and restore point into the MachineFrameInfo
attached to the MachineFunction.
This information is then used by the PrologEpilogInserter (PEI) to place the
related code at the right place. This pass runs right before the PEI.

Unlike the original paper of Chow from PLDI’88, this implementation of
shrink-wrapping does not use expensive data-flow analysis and does not need hack
to properly avoid frequently executed point. Instead, it relies on dominance and
loop properties.

The pass is off by default and each target can opt-in by setting the
EnableShrinkWrap boolean to true in their derived class of TargetPassConfig.
This setting can also be overwritten on the command line by using
-enable-shrink-wrap.

Before you try out the pass for your target, make sure you properly fix your
emitProlog/emitEpilog/adjustForXXX method to cope with basic blocks that are not
necessarily the entry block.


** Design Decisions **

1. ShrinkWrap is its own pass right now. It could frankly be merged into PEI but
for debugging and clarity I thought it was best to have its own file.
2. Right now, we only support one save point and one restore point. At some
point we can expand this to several save point and restore point, the impacted
component would then be:
- The pass itself: New algorithm needed.
- MachineFrameInfo: Hold a list or set of Save/Restore point instead of one
  pointer.
- PEI: Should loop over the save point and restore point.
Anyhow, at least for this first iteration, I do not believe this is interesting
to support the complex cases. We should revisit that when we motivating
examples.

Differential Revision: http://reviews.llvm.org/D9210

<rdar://problem/3201744>

llvm-svn: 236507

37 files changed, 632 insertions, 112 deletions

diff --git a/llvm/lib/CodeGen/CMakeLists.txt b/llvm/lib/CodeGen/CMakeLists.txt
index ef5763855a8..6ce5b13ea39 100644
--- a/llvm/lib/CodeGen/CMakeLists.txt
+++ b/llvm/lib/CodeGen/CMakeLists.txt
@@ -93,6 +93,7 @@ add_llvm_library(LLVMCodeGen
   ScheduleDAGInstrs.cpp
   ScheduleDAGPrinter.cpp
   ScoreboardHazardRecognizer.cpp
+  ShrinkWrap.cpp
   ShadowStackGC.cpp
   ShadowStackGCLowering.cpp
   SjLjEHPrepare.cpp
diff --git a/llvm/lib/CodeGen/CodeGen.cpp b/llvm/lib/CodeGen/CodeGen.cpp
index da66639d02f..2c6eaf35a25 100644
--- a/llvm/lib/CodeGen/CodeGen.cpp
+++ b/llvm/lib/CodeGen/CodeGen.cpp
@@ -61,6 +61,7 @@ void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializePostRASchedulerPass(Registry);
   initializeProcessImplicitDefsPass(Registry);
   initializeRegisterCoalescerPass(Registry);
+  initializeShrinkWrapPass(Registry);
   initializeSlotIndexesPass(Registry);
   initializeStackColoringPass(Registry);
   initializeStackMapLivenessPass(Registry);
diff --git a/llvm/lib/CodeGen/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index 448531fb716..fb0553b9414 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -600,8 +600,8 @@ MachineFrameInfo::getPristineRegs(const MachineBasicBlock *MBB) const {
   for (const MCPhysReg *CSR = TRI->getCalleeSavedRegs(MF); CSR && *CSR; ++CSR)
     BV.set(*CSR);
 
-  // The entry MBB always has all CSRs pristine.
-  if (MBB == &MF->front())
+  // Each MBB before the save point has all CSRs pristine.
+  if (isBeforeSavePoint(*MF, *MBB))
     return BV;
 
   // On other MBBs the saved CSRs are not pristine.
@@ -613,6 +613,40 @@ MachineFrameInfo::getPristineRegs(const MachineBasicBlock *MBB) const {
   return BV;
 }
 
+// Note: We could use some sort of caching mecanism, but we lack the ability
+// to know when the cache is invalid, i.e., the CFG changed.
+// Assuming we have that, we can simply compute all the set of MBBs
+// that are before the save point.
+bool MachineFrameInfo::isBeforeSavePoint(const MachineFunction &MF,
+                                         const MachineBasicBlock &MBB) const {
+  // Early exit if shrink-wrapping did not kick.
+  if (!Save)
+    return &MBB == &MF.front();
+
+  // Starting from MBB, check if there is a path leading to Save that do
+  // not cross Restore.
+  SmallPtrSet<const MachineBasicBlock *, 8> Visited;
+  SmallVector<const MachineBasicBlock *, 8> WorkList;
+  WorkList.push_back(&MBB);
+  Visited.insert(&MBB);
+  do {
+    const MachineBasicBlock *CurBB = WorkList.pop_back_val();
+    // By construction, the region that is after the save point is
+    // dominated by the Save and post-dominated by the Restore.
+    // If we do not reach Restore and still reach Save, this
+    // means MBB is before Save.
+    if (CurBB == Save)
+      return true;
+    if (CurBB == Restore)
+      continue;
+    // Enqueue all the successors not already visited.
+    for (MachineBasicBlock *SuccBB : CurBB->successors())
+      if (Visited.insert(SuccBB).second)
+        WorkList.push_back(SuccBB);
+  } while (!WorkList.empty());
+  return false;
+}
+
 unsigned MachineFrameInfo::estimateStackSize(const MachineFunction &MF) const {
   const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
   const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
diff --git a/llvm/lib/CodeGen/Passes.cpp b/llvm/lib/CodeGen/Passes.cpp
index c128414c0b3..690224342f6 100644
--- a/llvm/lib/CodeGen/Passes.cpp
+++ b/llvm/lib/CodeGen/Passes.cpp
@@ -52,7 +52,10 @@ static cl::opt<bool> DisableMachineLICM("disable-machine-licm", cl::Hidden,
 static cl::opt<bool> DisableMachineCSE("disable-machine-cse", cl::Hidden,
     cl::desc("Disable Machine Common Subexpression Elimination"));
 static cl::opt<cl::boolOrDefault>
-OptimizeRegAlloc("optimize-regalloc", cl::Hidden,
+    EnableShrinkWrapOpt("enable-shrink-wrap", cl::Hidden,
+                        cl::desc("enable the shrink-wrapping pass"));
+static cl::opt<cl::boolOrDefault> OptimizeRegAlloc(
+    "optimize-regalloc", cl::Hidden,
     cl::desc("Enable optimized register allocation compilation path."));
 static cl::opt<bool> DisablePostRAMachineLICM("disable-postra-machine-licm",
     cl::Hidden,
@@ -206,10 +209,10 @@ TargetPassConfig::~TargetPassConfig() {
 // Out of line constructor provides default values for pass options and
 // registers all common codegen passes.
 TargetPassConfig::TargetPassConfig(TargetMachine *tm, PassManagerBase &pm)
-  : ImmutablePass(ID), PM(&pm), StartAfter(nullptr), StopAfter(nullptr),
-    Started(true), Stopped(false), AddingMachinePasses(false), TM(tm),
-    Impl(nullptr), Initialized(false), DisableVerify(false),
-    EnableTailMerge(true) {
+    : ImmutablePass(ID), PM(&pm), StartAfter(nullptr), StopAfter(nullptr),
+      Started(true), Stopped(false), AddingMachinePasses(false), TM(tm),
+      Impl(nullptr), Initialized(false), DisableVerify(false),
+      EnableTailMerge(true), EnableShrinkWrap(false) {
 
   Impl = new PassConfigImpl();
 
@@ -524,6 +527,8 @@ void TargetPassConfig::addMachinePasses() {
   addPostRegAlloc();
 
   // Insert prolog/epilog code.  Eliminate abstract frame index references...
+  if (getEnableShrinkWrap())
+    addPass(&ShrinkWrapID);
   addPass(&PrologEpilogCodeInserterID);
 
   /// Add passes that optimize machine instructions after register allocation.
@@ -599,6 +604,21 @@ void TargetPassConfig::addMachineSSAOptimization() {
   addPass(&DeadMachineInstructionElimID);
 }
 
+bool TargetPassConfig::getEnableShrinkWrap() const {
+  switch (EnableShrinkWrapOpt) {
+  case cl::BOU_UNSET:
+    return EnableShrinkWrap && getOptLevel() != CodeGenOpt::None;
+  // If EnableShrinkWrap is set, it takes precedence on whatever the
+  // target sets. The rational is that we assume we want to test
+  // something related to shrink-wrapping.
+  case cl::BOU_TRUE:
+    return true;
+  case cl::BOU_FALSE:
+    return false;
+  }
+  llvm_unreachable("Invalid shrink-wrapping state");
+}
+
 //===---------------------------------------------------------------------===//
 /// Register Allocation Pass Configuration
 //===---------------------------------------------------------------------===//
diff --git a/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
index 5334a633ead..e4f359c213c 100644
--- a/llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -71,9 +71,9 @@ private:
   // stack frame indexes.
   unsigned MinCSFrameIndex, MaxCSFrameIndex;
 
-  // Entry and return blocks of the current function.
-  MachineBasicBlock *EntryBlock;
-  SmallVector<MachineBasicBlock *, 4> ReturnBlocks;
+  // Save and Restore blocks of the current function.
+  MachineBasicBlock *SaveBlock;
+  SmallVector<MachineBasicBlock *, 4> RestoreBlocks;
 
   // Flag to control whether to use the register scavenger to resolve
   // frame index materialization registers. Set according to
@@ -133,20 +133,26 @@ bool PEI::isReturnBlock(MachineBasicBlock* MBB) {
 
 /// Compute the set of return blocks
 void PEI::calculateSets(MachineFunction &Fn) {
-  // Sets used to compute spill, restore placement sets.
-  const std::vector<CalleeSavedInfo> &CSI =
-    Fn.getFrameInfo()->getCalleeSavedInfo();
+  const MachineFrameInfo *MFI = Fn.getFrameInfo();
 
-  // If no CSRs used, we are done.
-  if (CSI.empty())
+  // Even when we do not change any CSR, we still want to insert the
+  // prologue and epilogue of the function.
+  // So set the save points for those.
+
+  // Use the points found by shrink-wrapping, if any.
+  if (MFI->getSavePoint()) {
+    SaveBlock = MFI->getSavePoint();
+    assert(MFI->getRestorePoint() && "Both restore and save must be set");
+    RestoreBlocks.push_back(MFI->getRestorePoint());
     return;
+  }
 
   // Save refs to entry and return blocks.
-  EntryBlock = Fn.begin();
+  SaveBlock = Fn.begin();
   for (MachineFunction::iterator MBB = Fn.begin(), E = Fn.end();
        MBB != E; ++MBB)
     if (isReturnBlock(MBB))
-      ReturnBlocks.push_back(MBB);
+      RestoreBlocks.push_back(MBB);
 
   return;
 }
@@ -226,7 +232,7 @@ bool PEI::runOnMachineFunction(MachineFunction &Fn) {
   }
 
   delete RS;
-  ReturnBlocks.clear();
+  RestoreBlocks.clear();
   return true;
 }
 
@@ -372,6 +378,61 @@ void PEI::calculateCalleeSavedRegisters(MachineFunction &F) {
   MFI->setCalleeSavedInfo(CSI);
 }
 
+/// Helper function to update the liveness information for the callee-saved
+/// registers.
+static void updateLiveness(MachineFunction &MF) {
+  MachineFrameInfo *MFI = MF.getFrameInfo();
+  // Visited will contain all the basic blocks that are in the region
+  // where the callee saved registers are alive:
+  // - Anything that is not Save or Restore -> LiveThrough.
+  // - Save -> LiveIn.
+  // - Restore -> LiveOut.
+  // The live-out is not attached to the block, so no need to keep
+  // Restore in this set.
+  SmallPtrSet<MachineBasicBlock *, 8> Visited;
+  SmallVector<MachineBasicBlock *, 8> WorkList;
+  MachineBasicBlock *Entry = &MF.front();
+  MachineBasicBlock *Save = MFI->getSavePoint();
+
+  if (!Save)
+    Save = Entry;
+
+  if (Entry != Save) {
+    WorkList.push_back(Entry);
+    Visited.insert(Entry);
+  }
+  Visited.insert(Save);
+
+  MachineBasicBlock *Restore = MFI->getRestorePoint();
+  if (Restore)
+    // By construction Restore cannot be visited, otherwise it
+    // means there exists a path to Restore that does not go
+    // through Save.
+    WorkList.push_back(Restore);
+
+  while (!WorkList.empty()) {
+    const MachineBasicBlock *CurBB = WorkList.pop_back_val();
+    // By construction, the region that is after the save point is
+    // dominated by the Save and post-dominated by the Restore.
+    if (CurBB == Save)
+      continue;
+    // Enqueue all the successors not already visited.
+    // Those are by construction either before Save or after Restore.
+    for (MachineBasicBlock *SuccBB : CurBB->successors())
+      if (Visited.insert(SuccBB).second)
+        WorkList.push_back(SuccBB);
+  }
+
+  const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo();
+
+  for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
+    for (MachineBasicBlock *MBB : Visited)
+      // Add the callee-saved register as live-in.
+      // It's killed at the spill.
+      MBB->addLiveIn(CSI[i].getReg());
+  }
+}
+
 /// insertCSRSpillsAndRestores - Insert spill and restore code for
 /// callee saved registers used in the function.
 ///
@@ -392,26 +453,22 @@ void PEI::insertCSRSpillsAndRestores(MachineFunction &Fn) {
   MachineBasicBlock::iterator I;
 
   // Spill using target interface.
-  I = EntryBlock->begin();
-  if (!TFI->spillCalleeSavedRegisters(*EntryBlock, I, CSI, TRI)) {
+  I = SaveBlock->begin();
+  if (!TFI->spillCalleeSavedRegisters(*SaveBlock, I, CSI, TRI)) {
     for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
-      // Add the callee-saved register as live-in.
-      // It's killed at the spill.
-      EntryBlock->addLiveIn(CSI[i].getReg());
-
       // Insert the spill to the stack frame.
       unsigned Reg = CSI[i].getReg();
       const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
-      TII.storeRegToStackSlot(*EntryBlock, I, Reg, true, CSI[i].getFrameIdx(),
+      TII.storeRegToStackSlot(*SaveBlock, I, Reg, true, CSI[i].getFrameIdx(),
                               RC, TRI);
     }
   }
+  // Update the live-in information of all the blocks up to the save point.
+  updateLiveness(Fn);
 
   // Restore using target interface.
-  for (unsigned ri = 0, re = ReturnBlocks.size(); ri != re; ++ri) {
-    MachineBasicBlock *MBB = ReturnBlocks[ri];
+  for (MachineBasicBlock *MBB : RestoreBlocks) {
     I = MBB->end();
-    --I;
 
     // Skip over all terminator instructions, which are part of the return
     // sequence.
@@ -721,21 +778,18 @@ void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
   const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
 
   // Add prologue to the function...
-  TFI.emitPrologue(Fn);
+  TFI.emitPrologue(Fn, *SaveBlock);
 
-  // Add epilogue to restore the callee-save registers in each exiting block
-  for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
-    // If last instruction is a return instruction, add an epilogue
-    if (!I->empty() && I->back().isReturn())
-      TFI.emitEpilogue(Fn, *I);
-  }
+  // Add epilogue to restore the callee-save registers in each exiting block.
+  for (MachineBasicBlock *RestoreBlock : RestoreBlocks)
+    TFI.emitEpilogue(Fn, *RestoreBlock);
 
   // Emit additional code that is required to support segmented stacks, if
   // we've been asked for it.  This, when linked with a runtime with support
   // for segmented stacks (libgcc is one), will result in allocating stack
   // space in small chunks instead of one large contiguous block.
   if (Fn.shouldSplitStack())
-    TFI.adjustForSegmentedStacks(Fn);
+    TFI.adjustForSegmentedStacks(Fn, *SaveBlock);
 
   // Emit additional code that is required to explicitly handle the stack in
   // HiPE native code (if needed) when loaded in the Erlang/OTP runtime. The
@@ -743,7 +797,7 @@ void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
   // different conditional check and another BIF for allocating more stack
   // space.
   if (Fn.getFunction()->getCallingConv() == CallingConv::HiPE)
-    TFI.adjustForHiPEPrologue(Fn);
+    TFI.adjustForHiPEPrologue(Fn, *SaveBlock);
 }
 
 /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
diff --git a/llvm/lib/CodeGen/ShrinkWrap.cpp b/llvm/lib/CodeGen/ShrinkWrap.cpp
new file mode 100644
index 00000000000..56f1200619c
--- /dev/null
+++ b/llvm/lib/CodeGen/ShrinkWrap.cpp
@@ -0,0 +1,383 @@
+//===-- ShrinkWrap.cpp - Compute safe point for prolog/epilog insertion ---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass looks for safe point where the prologue and epilogue can be
+// inserted.
+// The safe point for the prologue (resp. epilogue) is called Save
+// (resp. Restore).
+// A point is safe for prologue (resp. epilogue) if and only if
+// it 1) dominates (resp. post-dominates) all the frame related operations and
+// between 2) two executions of the Save (resp. Restore) point there is an
+// execution of the Restore (resp. Save) point.
+//
+// For instance, the following points are safe:
+// for (int i = 0; i < 10; ++i) {
+//   Save
+//   ...
+//   Restore
+// }
+// Indeed, the execution looks like Save -> Restore -> Save -> Restore ...
+// And the following points are not:
+// for (int i = 0; i < 10; ++i) {
+//   Save
+//   ...
+// }
+// for (int i = 0; i < 10; ++i) {
+//   ...
+//   Restore
+// }
+// Indeed, the execution looks like Save -> Save -> ... -> Restore -> Restore.
+//
+// This pass also ensures that the safe points are 3) cheaper than the regular
+// entry and exits blocks.
+//
+// Property #1 is ensured via the use of MachineDominatorTree and
+// MachinePostDominatorTree.
+// Property #2 is ensured via property #1 and MachineLoopInfo, i.e., both
+// points must be in the same loop.
+// Property #3 is ensured via the MachineBlockFrequencyInfo.
+//
+// If this pass found points matching all this properties, then
+// MachineFrameInfo is updated this that information.
+//===----------------------------------------------------------------------===//
+#include "llvm/ADT/Statistic.h"
+// To check for profitability.
+#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
+// For property #1 for Save.
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+// To record the result of the analysis.
+#include "llvm/CodeGen/MachineFrameInfo.h"
+// For property #2.
+#include "llvm/CodeGen/MachineLoopInfo.h"
+// For property #1 for Restore.
+#include "llvm/CodeGen/MachinePostDominators.h"
+#include "llvm/CodeGen/Passes.h"
+// To know about callee-saved.
+#include "llvm/CodeGen/RegisterClassInfo.h"
+#include "llvm/Support/Debug.h"
+// To know about frame setup operation.
+#include "llvm/Target/TargetInstrInfo.h"
+// To access TargetInstrInfo.
+#include "llvm/Target/TargetSubtargetInfo.h"
+
+#define DEBUG_TYPE "shrink-wrap"
+
+using namespace llvm;
+
+STATISTIC(NumFunc, "Number of functions");
+STATISTIC(NumCandidates, "Number of shrink-wrapping candidates");
+STATISTIC(NumCandidatesDropped,
+          "Number of shrink-wrapping candidates dropped because of frequency");
+
+namespace {
+/// \brief Class to determine where the safe point to insert the
+/// prologue and epilogue are.
+/// Unlike the paper from Fred C. Chow, PLDI'88, that introduces the
+/// shrink-wrapping term for prologue/epilogue placement, this pass
+/// does not rely on expensive data-flow analysis. Instead we use the
+/// dominance properties and loop information to decide which point
+/// are safe for such insertion.
+class ShrinkWrap : public MachineFunctionPass {
+  /// Hold callee-saved information.
+  RegisterClassInfo RCI;
+  MachineDominatorTree *MDT;
+  MachinePostDominatorTree *MPDT;
+  /// Current safe point found for the prologue.
+  /// The prologue will be inserted before the first instruction
+  /// in this basic block.
+  MachineBasicBlock *Save;
+  /// Current safe point found for the epilogue.
+  /// The epilogue will be inserted before the first terminator instruction
+  /// in this basic block.
+  MachineBasicBlock *Restore;
+  /// Hold the information of the basic block frequency.
+  /// Use to check the profitability of the new points.
+  MachineBlockFrequencyInfo *MBFI;
+  /// Hold the loop information. Used to determine if Save and Restore
+  /// are in the same loop.
+  MachineLoopInfo *MLI;
+  /// Frequency of the Entry block.
+  uint64_t EntryFreq;
+  /// Current opcode for frame setup.
+  int FrameSetupOpcode;
+  /// Current opcode for frame destroy.
+  int FrameDestroyOpcode;
+  /// Entry block.
+  const MachineBasicBlock *Entry;
+
+  /// \brief Check if \p MI uses or defines a callee-saved register or
+  /// a frame index. If this is the case, this means \p MI must happen
+  /// after Save and before Restore.
+  bool useOrDefCSROrFI(const MachineInstr &MI) const;
+
+  /// \brief Update the Save and Restore points such that \p MBB is in
+  /// the region that is dominated by Save and post-dominated by Restore
+  /// and Save and Restore still match the safe point definition.
+  /// Such point may not exist and Save and/or Restore may be null after
+  /// this call.
+  void updateSaveRestorePoints(MachineBasicBlock &MBB);
+
+  /// \brief Initialize the pass for \p MF.
+  void init(MachineFunction &MF) {
+    RCI.runOnMachineFunction(MF);
+    MDT = &getAnalysis<MachineDominatorTree>();
+    MPDT = &getAnalysis<MachinePostDominatorTree>();
+    Save = nullptr;
+    Restore = nullptr;
+    MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
+    MLI = &getAnalysis<MachineLoopInfo>();
+    EntryFreq = MBFI->getEntryFreq();
+    const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
+    FrameSetupOpcode = TII.getCallFrameSetupOpcode();
+    FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
+    Entry = &MF.front();
+
+    ++NumFunc;
+  }
+
+  /// Check whether or not Save and Restore points are still interesting for
+  /// shrink-wrapping.
+  bool ArePointsInteresting() const { return Save != Entry && Save && Restore; }
+
+public:
+  static char ID;
+
+  ShrinkWrap() : MachineFunctionPass(ID) {
+    initializeShrinkWrapPass(*PassRegistry::getPassRegistry());
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesAll();
+    AU.addRequired<MachineBlockFrequencyInfo>();
+    AU.addRequired<MachineDominatorTree>();
+    AU.addRequired<MachinePostDominatorTree>();
+    AU.addRequired<MachineLoopInfo>();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
+  const char *getPassName() const override {
+    return "Shrink Wrapping analysis";
+  }
+
+  /// \brief Perform the shrink-wrapping analysis and update
+  /// the MachineFrameInfo attached to \p MF with the results.
+  bool runOnMachineFunction(MachineFunction &MF) override;
+};
+} // End anonymous namespace.
+
+char ShrinkWrap::ID = 0;
+char &llvm::ShrinkWrapID = ShrinkWrap::ID;
+
+INITIALIZE_PASS_BEGIN(ShrinkWrap, "shrink-wrap", "Shrink Wrap Pass", false,
+                      false)
+INITIALIZE_PASS_DEPENDENCY(MachineBlockFrequencyInfo)
+INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
+INITIALIZE_PASS_DEPENDENCY(MachinePostDominatorTree)
+INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
+INITIALIZE_PASS_END(ShrinkWrap, "shrink-wrap", "Shrink Wrap Pass", false, false)
+
+bool ShrinkWrap::useOrDefCSROrFI(const MachineInstr &MI) const {
+  if (MI.getOpcode() == FrameSetupOpcode ||
+      MI.getOpcode() == FrameDestroyOpcode) {
+    DEBUG(dbgs() << "Frame instruction: " << MI << '\n');
+    return true;
+  }
+  for (const MachineOperand &MO : MI.operands()) {
+    bool UseCSR = false;
+    if (MO.isReg()) {
+      unsigned PhysReg = MO.getReg();
+      if (!PhysReg)
+        continue;
+      assert(TargetRegisterInfo::isPhysicalRegister(PhysReg) &&
+             "Unallocated register?!");
+      UseCSR = RCI.getLastCalleeSavedAlias(PhysReg);
+    }
+    // TODO: Handle regmask more accurately.
+    // For now, be conservative about them.
+    if (UseCSR || MO.isFI() || MO.isRegMask()) {
+      DEBUG(dbgs() << "Use or define CSR(" << UseCSR << ") or FI(" << MO.isFI()
+                   << "): " << MI << '\n');
+      return true;
+    }
+  }
+  return false;
+}
+
+/// \brief Helper function to find the immediate (post) dominator.
+template <typename ListOfBBs, typename DominanceAnalysis>
+MachineBasicBlock *FindIDom(MachineBasicBlock &Block, ListOfBBs BBs,
+                            DominanceAnalysis &Dom) {
+  MachineBasicBlock *IDom = &Block;
+  for (MachineBasicBlock *BB : BBs) {
+    IDom = Dom.findNearestCommonDominator(IDom, BB);
+    if (!IDom)
+      break;
+  }
+  return IDom;
+}
+
+void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB) {
+  // Get rid of the easy cases first.
+  if (!Save)
+    Save = &MBB;
+  else
+    Save = MDT->findNearestCommonDominator(Save, &MBB);
+
+  if (!Save) {
+    DEBUG(dbgs() << "Found a block that is not reachable from Entry\n");
+    return;
+  }
+
+  if (!Restore)
+    Restore = &MBB;
+  else
+    Restore = MPDT->findNearestCommonDominator(Restore, &MBB);
+
+  // Make sure we would be able to insert the restore code before the
+  // terminator.
+  if (Restore == &MBB) {
+    for (const MachineInstr &Terminator : MBB.terminators()) {
+      if (!useOrDefCSROrFI(Terminator))
+        continue;
+      // One of the terminator needs to happen before the restore point.
+      if (MBB.succ_empty()) {
+        Restore = nullptr;
+        break;
+      }
+      // Look for a restore point that post-dominates all the successors.
+      // The immediate post-dominator is what we are looking for.
+      Restore = FindIDom<>(*Restore, Restore->successors(), *MPDT);
+      break;
+    }
+  }
+
+  if (!Restore) {
+    DEBUG(dbgs() << "Restore point needs to be spanned on several blocks\n");
+    return;
+  }
+
+  // Make sure Save and Restore are suitable for shrink-wrapping:
+  // 1. all path from Save needs to lead to Restore before exiting.
+  // 2. all path to Restore needs to go through Save from Entry.
+  // We achieve that by making sure that:
+  // A. Save dominates Restore.
+  // B. Restore post-dominates Save.
+  // C. Save and Restore are in the same loop.
+  bool SaveDominatesRestore = false;
+  bool RestorePostDominatesSave = false;
+  while (Save && Restore &&
+         (!(SaveDominatesRestore = MDT->dominates(Save, Restore)) ||
+          !(RestorePostDominatesSave = MPDT->dominates(Restore, Save)) ||
+          MLI->getLoopFor(Save) != MLI->getLoopFor(Restore))) {
+    // Fix (A).
+    if (!SaveDominatesRestore) {
+      Save = MDT->findNearestCommonDominator(Save, Restore);
+      continue;
+    }
+    // Fix (B).
+    if (!RestorePostDominatesSave)
+      Restore = MPDT->findNearestCommonDominator(Restore, Save);
+
+    // Fix (C).
+    if (Save && Restore && Save != Restore &&
+        MLI->getLoopFor(Save) != MLI->getLoopFor(Restore)) {
+      if (MLI->getLoopDepth(Save) > MLI->getLoopDepth(Restore))
+        // Push Save outside of this loop.
+        Save = FindIDom<>(*Save, Save->predecessors(), *MDT);
+      else
+        // Push Restore outside of this loop.
+        Restore = FindIDom<>(*Restore, Restore->successors(), *MPDT);
+    }
+  }
+}
+
+bool ShrinkWrap::runOnMachineFunction(MachineFunction &MF) {
+  if (MF.empty())
+    return false;
+  DEBUG(dbgs() << "**** Analysing " << MF.getName() << '\n');
+
+  init(MF);
+
+  for (MachineBasicBlock &MBB : MF) {
+    DEBUG(dbgs() << "Look into: " << MBB.getNumber() << ' ' << MBB.getName()
+                 << '\n');
+
+    for (const MachineInstr &MI : MBB) {
+      if (!useOrDefCSROrFI(MI))
+        continue;
+      // Save (resp. restore) point must dominate (resp. post dominate)
+      // MI. Look for the proper basic block for those.
+      updateSaveRestorePoints(MBB);
+      // If we are at a point where we cannot improve the placement of
+      // save/restore instructions, just give up.
+      if (!ArePointsInteresting()) {
+        DEBUG(dbgs() << "No Shrink wrap candidate found\n");
+        return false;
+      }
+      // No need to look for other instructions, this basic block
+      // will already be part of the handled region.
+      break;
+    }
+  }
+  if (!ArePointsInteresting()) {
+    // If the points are not interesting at this point, then they must be null
+    // because it means we did not encounter any frame/CSR related code.
+    // Otherwise, we would have returned from the previous loop.
+    assert(!Save && !Restore && "We miss a shrink-wrap opportunity?!");
+    DEBUG(dbgs() << "Nothing to shrink-wrap\n");
+    return false;
+  }
+
+  DEBUG(dbgs() << "\n ** Results **\nFrequency of the Entry: " << EntryFreq
+               << '\n');
+
+  do {
+    DEBUG(dbgs() << "Shrink wrap candidates (#, Name, Freq):\nSave: "
+                 << Save->getNumber() << ' ' << Save->getName() << ' '
+                 << MBFI->getBlockFreq(Save).getFrequency() << "\nRestore: "
+                 << Restore->getNumber() << ' ' << Restore->getName() << ' '
+                 << MBFI->getBlockFreq(Restore).getFrequency() << '\n');
+
+    bool IsSaveCheap;
+    if ((IsSaveCheap = EntryFreq >= MBFI->getBlockFreq(Save).getFrequency()) &&
+        EntryFreq >= MBFI->getBlockFreq(Restore).getFrequency())
+      break;
+    DEBUG(dbgs() << "New points are too expensive\n");
+    MachineBasicBlock *NewBB;
+    if (!IsSaveCheap) {
+      Save = FindIDom<>(*Save, Save->predecessors(), *MDT);
+      if (!Save)
+        break;
+      NewBB = Save;
+    } else {
+      // Restore is expensive.
+      Restore = FindIDom<>(*Restore, Restore->successors(), *MPDT);
+      if (!Restore)
+        break;
+      NewBB = Restore;
+    }
+    updateSaveRestorePoints(*NewBB);
+  } while (Save && Restore);
+
+  if (!ArePointsInteresting()) {
+    ++NumCandidatesDropped;
+    return false;
+  }
+
+  DEBUG(dbgs() << "Final shrink wrap candidates:\nSave: " << Save->getNumber()
+               << ' ' << Save->getName() << "\nRestore: "
+               << Restore->getNumber() << ' ' << Restore->getName() << '\n');
+
+  MachineFrameInfo *MFI = MF.getFrameInfo();
+  MFI->setSavePoint(Save);
+  MFI->setRestorePoint(Restore);
+  ++NumCandidates;
+  return false;
+}
diff --git a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
index 6f133a35dce..7146f592a96 100644
--- a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -275,8 +275,8 @@ static bool isCSSave(MachineInstr *MBBI) {
          MBBI->getOpcode() == AArch64::STPDpre;
 }
 
-void AArch64FrameLowering::emitPrologue(MachineFunction &MF) const {
-  MachineBasicBlock &MBB = MF.front(); // Prologue goes in entry BB.
+void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
+                                        MachineBasicBlock &MBB) const {
   MachineBasicBlock::iterator MBBI = MBB.begin();
   const MachineFrameInfo *MFI = MF.getFrameInfo();
   const Function *Fn = MF.getFunction();
@@ -539,15 +539,19 @@ static bool isCSRestore(MachineInstr *MI, const MCPhysReg *CSRegs) {
 void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
                                         MachineBasicBlock &MBB) const {
   MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
-  assert(MBBI->isReturn() && "Can only insert epilog into returning blocks");
   MachineFrameInfo *MFI = MF.getFrameInfo();
   const AArch64InstrInfo *TII =
       static_cast<const AArch64InstrInfo *>(MF.getSubtarget().getInstrInfo());
   const AArch64RegisterInfo *RegInfo = static_cast<const AArch64RegisterInfo *>(
       MF.getSubtarget().getRegisterInfo());
-  DebugLoc DL = MBBI->getDebugLoc();
-  unsigned RetOpcode = MBBI->getOpcode();
-
+  DebugLoc DL;
+  bool IsTailCallReturn = false;
+  if (MBB.end() != MBBI) {
+    DL = MBBI->getDebugLoc();
+    unsigned RetOpcode = MBBI->getOpcode();
+    IsTailCallReturn = RetOpcode == AArch64::TCRETURNdi ||
+      RetOpcode == AArch64::TCRETURNri;
+  }
   int NumBytes = MFI->getStackSize();
   const AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
 
@@ -559,7 +563,7 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
   // Initial and residual are named for consistency with the prologue. Note that
   // in the epilogue, the residual adjustment is executed first.
   uint64_t ArgumentPopSize = 0;
-  if (RetOpcode == AArch64::TCRETURNdi || RetOpcode == AArch64::TCRETURNri) {
+  if (IsTailCallReturn) {
     MachineOperand &StackAdjust = MBBI->getOperand(1);
 
     // For a tail-call in a callee-pops-arguments environment, some or all of
@@ -604,7 +608,7 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
 
   unsigned NumRestores = 0;
   // Move past the restores of the callee-saved registers.
-  MachineBasicBlock::iterator LastPopI = MBBI;
+  MachineBasicBlock::iterator LastPopI = MBB.getFirstTerminator();
   const MCPhysReg *CSRegs = RegInfo->getCalleeSavedRegs(&MF);
   if (LastPopI != MBB.begin()) {
     do {
diff --git a/llvm/lib/Target/AArch64/AArch64FrameLowering.h b/llvm/lib/Target/AArch64/AArch64FrameLowering.h
index 1439bf32085..b496fccba34 100644
--- a/llvm/lib/Target/AArch64/AArch64FrameLowering.h
+++ b/llvm/lib/Target/AArch64/AArch64FrameLowering.h
@@ -34,7 +34,7 @@ public:
 
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   int getFrameIndexOffset(const MachineFunction &MF, int FI) const override;
diff --git a/llvm/lib/Target/ARM/ARMFrameLowering.cpp b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
index 92fe8fe5fbc..4eafd82af4c 100644
--- a/llvm/lib/Target/ARM/ARMFrameLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
@@ -278,8 +278,9 @@ static void emitAligningInstructions(MachineFunction &MF, ARMFunctionInfo *AFI,
   }
 }
 
-void ARMFrameLowering::emitPrologue(MachineFunction &MF) const {
-  MachineBasicBlock &MBB = MF.front();
+void ARMFrameLowering::emitPrologue(MachineFunction &MF,
+                                    MachineBasicBlock &MBB) const {
+  assert(&MBB == &MF.front() && "Shrink-wrapping not yet implemented");
   MachineBasicBlock::iterator MBBI = MBB.begin();
   MachineFrameInfo  *MFI = MF.getFrameInfo();
   ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
@@ -1861,7 +1862,8 @@ static const uint64_t kSplitStackAvailable = 256;
 // ARM can be found at [1].
 //
 // [1] - https://github.com/mozilla/rust/blob/86efd9/src/rt/arch/arm/morestack.S
-void ARMFrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
+void ARMFrameLowering::adjustForSegmentedStacks(
+    MachineFunction &MF, MachineBasicBlock &PrologueMBB) const {
   unsigned Opcode;
   unsigned CFIIndex;
   const ARMSubtarget *ST = &MF.getSubtarget<ARMSubtarget>();
@@ -1874,7 +1876,7 @@ void ARMFrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
   if (!ST->isTargetAndroid() && !ST->isTargetLinux())
     report_fatal_error("Segmented stacks not supported on this platform.");
 
-  MachineBasicBlock &prologueMBB = MF.front();
+  assert(&PrologueMBB == &MF.front() && "Shrink-wrapping not yet implemented");
   MachineFrameInfo *MFI = MF.getFrameInfo();
   MachineModuleInfo &MMI = MF.getMMI();
   MCContext &Context = MMI.getContext();
@@ -1902,8 +1904,8 @@ void ARMFrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
   MachineBasicBlock *GetMBB = MF.CreateMachineBasicBlock();
   MachineBasicBlock *McrMBB = MF.CreateMachineBasicBlock();
 
-  for (MachineBasicBlock::livein_iterator i = prologueMBB.livein_begin(),
-                                          e = prologueMBB.livein_end();
+  for (MachineBasicBlock::livein_iterator i = PrologueMBB.livein_begin(),
+                                          e = PrologueMBB.livein_end();
        i != e; ++i) {
     AllocMBB->addLiveIn(*i);
     GetMBB->addLiveIn(*i);
@@ -2156,7 +2158,7 @@ void ARMFrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
       .addCFIIndex(CFIIndex);
 
   // Organizing MBB lists
-  PostStackMBB->addSuccessor(&prologueMBB);
+  PostStackMBB->addSuccessor(&PrologueMBB);
 
   AllocMBB->addSuccessor(PostStackMBB);
 
diff --git a/llvm/lib/Target/ARM/ARMFrameLowering.h b/llvm/lib/Target/ARM/ARMFrameLowering.h
index b7be43642ad..ff3425795ae 100644
--- a/llvm/lib/Target/ARM/ARMFrameLowering.h
+++ b/llvm/lib/Target/ARM/ARMFrameLowering.h
@@ -28,7 +28,7 @@ public:
 
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   void fixTCReturn(MachineFunction &MF, MachineBasicBlock &MBB) const;
@@ -55,7 +55,8 @@ public:
   void processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
                                             RegScavenger *RS) const override;
 
-  void adjustForSegmentedStacks(MachineFunction &MF) const override;
+  void adjustForSegmentedStacks(MachineFunction &MF,
+                                MachineBasicBlock &MBB) const override;
 
  private:
   void emitPushInst(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
diff --git a/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp b/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp
index c496cd7c759..77cd890e4ca 100644
--- a/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp
+++ b/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp
@@ -82,8 +82,9 @@ eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
   MBB.erase(I);
 }
 
-void Thumb1FrameLowering::emitPrologue(MachineFunction &MF) const {
-  MachineBasicBlock &MBB = MF.front();
+void Thumb1FrameLowering::emitPrologue(MachineFunction &MF,
+                                       MachineBasicBlock &MBB) const {
+  assert(&MBB == &MF.front() && "Shrink-wrapping not yet implemented");
   MachineBasicBlock::iterator MBBI = MBB.begin();
   MachineFrameInfo  *MFI = MF.getFrameInfo();
   ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
diff --git a/llvm/lib/Target/ARM/Thumb1FrameLowering.h b/llvm/lib/Target/ARM/Thumb1FrameLowering.h
index cf932035b8d..31d57325ebd 100644
--- a/llvm/lib/Target/ARM/Thumb1FrameLowering.h
+++ b/llvm/lib/Target/ARM/Thumb1FrameLowering.h
@@ -27,7 +27,7 @@ public:
 
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
diff --git a/llvm/lib/Target/BPF/BPFFrameLowering.cpp b/llvm/lib/Target/BPF/BPFFrameLowering.cpp
index ae9f35520de..54c5ececc7d 100644
--- a/llvm/lib/Target/BPF/BPFFrameLowering.cpp
+++ b/llvm/lib/Target/BPF/BPFFrameLowering.cpp
@@ -23,7 +23,8 @@ using namespace llvm;
 
 bool BPFFrameLowering::hasFP(const MachineFunction &MF) const { return true; }
 
-void BPFFrameLowering::emitPrologue(MachineFunction &MF) const {}
+void BPFFrameLowering::emitPrologue(MachineFunction &MF,
+                                    MachineBasicBlock &MBB) const {}
 
 void BPFFrameLowering::emitEpilogue(MachineFunction &MF,
                                     MachineBasicBlock &MBB) const {}
diff --git a/llvm/lib/Target/BPF/BPFFrameLowering.h b/llvm/lib/Target/BPF/BPFFrameLowering.h
index 833046ddab6..3b9fc443e05 100644
--- a/llvm/lib/Target/BPF/BPFFrameLowering.h
+++ b/llvm/lib/Target/BPF/BPFFrameLowering.h
@@ -24,7 +24,7 @@ public:
   explicit BPFFrameLowering(const BPFSubtarget &sti)
       : TargetFrameLowering(TargetFrameLowering::StackGrowsDown, 8, 0) {}
 
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   bool hasFP(const MachineFunction &MF) const override;
diff --git a/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp b/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
index ee025137dc0..3071b779413 100644
--- a/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
@@ -344,16 +344,17 @@ void HexagonFrameLowering::findShrunkPrologEpilog(MachineFunction &MF,
   EpilogB = PDomB;
 }
 
-
 /// Perform most of the PEI work here:
 /// - saving/restoring of the callee-saved registers,
 /// - stack frame creation and destruction.
 /// Normally, this work is distributed among various functions, but doing it
 /// in one place allows shrink-wrapping of the stack frame.
-void HexagonFrameLowering::emitPrologue(MachineFunction &MF) const {
+void HexagonFrameLowering::emitPrologue(MachineFunction &MF,
+                                        MachineBasicBlock &MBB) const {
   auto &HST = static_cast<const HexagonSubtarget&>(MF.getSubtarget());
   auto &HRI = *HST.getRegisterInfo();
 
+  assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
   MachineFrameInfo *MFI = MF.getFrameInfo();
   const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo();
 
diff --git a/llvm/lib/Target/Hexagon/HexagonFrameLowering.h b/llvm/lib/Target/Hexagon/HexagonFrameLowering.h
index 228a0442b47..89500cb8572 100644
--- a/llvm/lib/Target/Hexagon/HexagonFrameLowering.h
+++ b/llvm/lib/Target/Hexagon/HexagonFrameLowering.h
@@ -26,7 +26,8 @@ public:
   // All of the prolog/epilog functionality, including saving and restoring
   // callee-saved registers is handled in emitPrologue. This is to have the
   // logic for shrink-wrapping in one place.
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const
+      override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const
       override {}
   bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
diff --git a/llvm/lib/Target/MSP430/MSP430FrameLowering.cpp b/llvm/lib/Target/MSP430/MSP430FrameLowering.cpp
index d6cb9f6459a..eb720809e47 100644
--- a/llvm/lib/Target/MSP430/MSP430FrameLowering.cpp
+++ b/llvm/lib/Target/MSP430/MSP430FrameLowering.cpp
@@ -39,8 +39,9 @@ bool MSP430FrameLowering::hasReservedCallFrame(const MachineFunction &MF) const
   return !MF.getFrameInfo()->hasVarSizedObjects();
 }
 
-void MSP430FrameLowering::emitPrologue(MachineFunction &MF) const {
-  MachineBasicBlock &MBB = MF.front();   // Prolog goes in entry BB
+void MSP430FrameLowering::emitPrologue(MachineFunction &MF,
+                                       MachineBasicBlock &MBB) const {
+  assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
   MachineFrameInfo *MFI = MF.getFrameInfo();
   MSP430MachineFunctionInfo *MSP430FI = MF.getInfo<MSP430MachineFunctionInfo>();
   const MSP430InstrInfo &TII =
diff --git a/llvm/lib/Target/MSP430/MSP430FrameLowering.h b/llvm/lib/Target/MSP430/MSP430FrameLowering.h
index 1941af26e85..48c4dc866a6 100644
--- a/llvm/lib/Target/MSP430/MSP430FrameLowering.h
+++ b/llvm/lib/Target/MSP430/MSP430FrameLowering.h
@@ -27,7 +27,7 @@ public:
 
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   void eliminateCallFramePseudoInstr(MachineFunction &MF,
diff --git a/llvm/lib/Target/Mips/Mips16FrameLowering.cpp b/llvm/lib/Target/Mips/Mips16FrameLowering.cpp
index 5828fbdee40..db2a924a99f 100644
--- a/llvm/lib/Target/Mips/Mips16FrameLowering.cpp
+++ b/llvm/lib/Target/Mips/Mips16FrameLowering.cpp
@@ -32,8 +32,9 @@ using namespace llvm;
 Mips16FrameLowering::Mips16FrameLowering(const MipsSubtarget &STI)
     : MipsFrameLowering(STI, STI.stackAlignment()) {}
 
-void Mips16FrameLowering::emitPrologue(MachineFunction &MF) const {
-  MachineBasicBlock &MBB = MF.front();
+void Mips16FrameLowering::emitPrologue(MachineFunction &MF,
+                                       MachineBasicBlock &MBB) const {
+  assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
   MachineFrameInfo *MFI = MF.getFrameInfo();
   const Mips16InstrInfo &TII =
       *static_cast<const Mips16InstrInfo *>(STI.getInstrInfo());
diff --git a/llvm/lib/Target/Mips/Mips16FrameLowering.h b/llvm/lib/Target/Mips/Mips16FrameLowering.h
index 0287e59243a..f281c927c1c 100644
--- a/llvm/lib/Target/Mips/Mips16FrameLowering.h
+++ b/llvm/lib/Target/Mips/Mips16FrameLowering.h
@@ -23,7 +23,7 @@ public:
 
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
diff --git a/llvm/lib/Target/Mips/MipsSEFrameLowering.cpp b/llvm/lib/Target/Mips/MipsSEFrameLowering.cpp
index e9a206170a6..19efa59e1fd 100644
--- a/llvm/lib/Target/Mips/MipsSEFrameLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsSEFrameLowering.cpp
@@ -364,8 +364,9 @@ bool ExpandPseudo::expandExtractElementF64(MachineBasicBlock &MBB,
 MipsSEFrameLowering::MipsSEFrameLowering(const MipsSubtarget &STI)
     : MipsFrameLowering(STI, STI.stackAlignment()) {}
 
-void MipsSEFrameLowering::emitPrologue(MachineFunction &MF) const {
-  MachineBasicBlock &MBB   = MF.front();
+void MipsSEFrameLowering::emitPrologue(MachineFunction &MF,
+                                       MachineBasicBlock &MBB) const {
+  assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
   MachineFrameInfo *MFI    = MF.getFrameInfo();
   MipsFunctionInfo *MipsFI = MF.getInfo<MipsFunctionInfo>();
 
diff --git a/llvm/lib/Target/Mips/MipsSEFrameLowering.h b/llvm/lib/Target/Mips/MipsSEFrameLowering.h
index 22448a433b7..2fcd6bbb9a1 100644
--- a/llvm/lib/Target/Mips/MipsSEFrameLowering.h
+++ b/llvm/lib/Target/Mips/MipsSEFrameLowering.h
@@ -24,7 +24,7 @@ public:
 
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
diff --git a/llvm/lib/Target/NVPTX/NVPTXFrameLowering.cpp b/llvm/lib/Target/NVPTX/NVPTXFrameLowering.cpp
index 34d3a66adce..5503494fc3c 100644
--- a/llvm/lib/Target/NVPTX/NVPTXFrameLowering.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXFrameLowering.cpp
@@ -31,9 +31,10 @@ NVPTXFrameLowering::NVPTXFrameLowering()
 
 bool NVPTXFrameLowering::hasFP(const MachineFunction &MF) const { return true; }
 
-void NVPTXFrameLowering::emitPrologue(MachineFunction &MF) const {
+void NVPTXFrameLowering::emitPrologue(MachineFunction &MF,
+                                      MachineBasicBlock &MBB) const {
   if (MF.getFrameInfo()->hasStackObjects()) {
-    MachineBasicBlock &MBB = MF.front();
+    assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
     // Insert "mov.u32 %SP, %Depot"
     MachineBasicBlock::iterator MBBI = MBB.begin();
     // This instruction really occurs before first instruction
diff --git a/llvm/lib/Target/NVPTX/NVPTXFrameLowering.h b/llvm/lib/Target/NVPTX/NVPTXFrameLowering.h
index d1e0a5ceb30..14f8bb7b98f 100644
--- a/llvm/lib/Target/NVPTX/NVPTXFrameLowering.h
+++ b/llvm/lib/Target/NVPTX/NVPTXFrameLowering.h
@@ -23,7 +23,7 @@ public:
   explicit NVPTXFrameLowering();
 
   bool hasFP(const MachineFunction &MF) const override;
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   void
diff --git a/llvm/lib/Target/NVPTX/NVPTXPrologEpilogPass.cpp b/llvm/lib/Target/NVPTX/NVPTXPrologEpilogPass.cpp
index c1c67e3872e..5fd69a6815a 100644
--- a/llvm/lib/Target/NVPTX/NVPTXPrologEpilogPass.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXPrologEpilogPass.cpp
@@ -68,7 +68,7 @@ bool NVPTXPrologEpilogPass::runOnMachineFunction(MachineFunction &MF) {
   }
 
   // Add function prolog/epilog
-  TFI.emitPrologue(MF);
+  TFI.emitPrologue(MF, MF.front());
 
   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
     // If last instruction is a return instruction, add an epilogue
diff --git a/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp b/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
index f997fea4d93..b4008e4a886 100644
--- a/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
@@ -555,8 +555,9 @@ void PPCFrameLowering::replaceFPWithRealFP(MachineFunction &MF) const {
     }
 }
 
-void PPCFrameLowering::emitPrologue(MachineFunction &MF) const {
-  MachineBasicBlock &MBB = MF.front();   // Prolog goes in entry BB
+void PPCFrameLowering::emitPrologue(MachineFunction &MF,
+                                    MachineBasicBlock &MBB) const {
+  assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
   MachineBasicBlock::iterator MBBI = MBB.begin();
   MachineFrameInfo *MFI = MF.getFrameInfo();
   const PPCInstrInfo &TII =
diff --git a/llvm/lib/Target/PowerPC/PPCFrameLowering.h b/llvm/lib/Target/PowerPC/PPCFrameLowering.h
index dddabb80892..28d074ecd79 100644
--- a/llvm/lib/Target/PowerPC/PPCFrameLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCFrameLowering.h
@@ -38,7 +38,7 @@ public:
 
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   bool hasFP(const MachineFunction &MF) const override;
diff --git a/llvm/lib/Target/R600/AMDGPUFrameLowering.cpp b/llvm/lib/Target/R600/AMDGPUFrameLowering.cpp
index 9e8302ec0a1..8175786fb9b 100644
--- a/llvm/lib/Target/R600/AMDGPUFrameLowering.cpp
+++ b/llvm/lib/Target/R600/AMDGPUFrameLowering.cpp
@@ -99,9 +99,8 @@ AMDGPUFrameLowering::getCalleeSavedSpillSlots(unsigned &NumEntries) const {
   NumEntries = 0;
   return nullptr;
 }
-void
-AMDGPUFrameLowering::emitPrologue(MachineFunction &MF) const {
-}
+void AMDGPUFrameLowering::emitPrologue(MachineFunction &MF,
+                                       MachineBasicBlock &MBB) const {}
 void
 AMDGPUFrameLowering::emitEpilogue(MachineFunction &MF,
                                   MachineBasicBlock &MBB) const {
diff --git a/llvm/lib/Target/R600/AMDGPUFrameLowering.h b/llvm/lib/Target/R600/AMDGPUFrameLowering.h
index 15a6636a1ae..9f31be1af79 100644
--- a/llvm/lib/Target/R600/AMDGPUFrameLowering.h
+++ b/llvm/lib/Target/R600/AMDGPUFrameLowering.h
@@ -37,7 +37,7 @@ public:
   int getFrameIndexOffset(const MachineFunction &MF, int FI) const override;
   const SpillSlot *
     getCalleeSavedSpillSlots(unsigned &NumEntries) const override;
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   bool hasFP(const MachineFunction &MF) const override;
 };
diff --git a/llvm/lib/Target/Sparc/SparcFrameLowering.cpp b/llvm/lib/Target/Sparc/SparcFrameLowering.cpp
index a065d3a0803..bccc6bdd53e 100644
--- a/llvm/lib/Target/Sparc/SparcFrameLowering.cpp
+++ b/llvm/lib/Target/Sparc/SparcFrameLowering.cpp
@@ -82,10 +82,11 @@ void SparcFrameLowering::emitSPAdjustment(MachineFunction &MF,
     .addReg(SP::O6).addReg(SP::G1);
 }
 
-void SparcFrameLowering::emitPrologue(MachineFunction &MF) const {
+void SparcFrameLowering::emitPrologue(MachineFunction &MF,
+                                      MachineBasicBlock &MBB) const {
   SparcMachineFunctionInfo *FuncInfo = MF.getInfo<SparcMachineFunctionInfo>();
 
-  MachineBasicBlock &MBB = MF.front();
+  assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
   MachineFrameInfo *MFI = MF.getFrameInfo();
   const SparcInstrInfo &TII =
       *static_cast<const SparcInstrInfo *>(MF.getSubtarget().getInstrInfo());
diff --git a/llvm/lib/Target/Sparc/SparcFrameLowering.h b/llvm/lib/Target/Sparc/SparcFrameLowering.h
index 9e53994e3c3..bb3b78861cb 100644
--- a/llvm/lib/Target/Sparc/SparcFrameLowering.h
+++ b/llvm/lib/Target/Sparc/SparcFrameLowering.h
@@ -26,7 +26,7 @@ public:
 
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   void
diff --git a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
index eff4ae3baf3..a636b35635c 100644
--- a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
@@ -309,8 +309,9 @@ static void emitIncrement(MachineBasicBlock &MBB,
   }
 }
 
-void SystemZFrameLowering::emitPrologue(MachineFunction &MF) const {
-  MachineBasicBlock &MBB = MF.front();
+void SystemZFrameLowering::emitPrologue(MachineFunction &MF,
+                                        MachineBasicBlock &MBB) const {
+  assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
   MachineFrameInfo *MFFrame = MF.getFrameInfo();
   auto *ZII =
       static_cast<const SystemZInstrInfo *>(MF.getSubtarget().getInstrInfo());
diff --git a/llvm/lib/Target/SystemZ/SystemZFrameLowering.h b/llvm/lib/Target/SystemZ/SystemZFrameLowering.h
index cefa56fd74e..60bad894ee4 100644
--- a/llvm/lib/Target/SystemZ/SystemZFrameLowering.h
+++ b/llvm/lib/Target/SystemZ/SystemZFrameLowering.h
@@ -40,7 +40,7 @@ public:
     override;
   void processFunctionBeforeFrameFinalized(MachineFunction &MF,
                                            RegScavenger *RS) const override;
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   bool hasFP(const MachineFunction &MF) const override;
   int getFrameIndexOffset(const MachineFunction &MF, int FI) const override;
diff --git a/llvm/lib/Target/X86/X86FrameLowering.cpp b/llvm/lib/Target/X86/X86FrameLowering.cpp
index 1d2c73c4308..a25643b2e2e 100644
--- a/llvm/lib/Target/X86/X86FrameLowering.cpp
+++ b/llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -565,8 +565,9 @@ static uint64_t calculateMaxStackAlign(const MachineFunction &MF) {
   - for 32-bit code, substitute %e?? registers for %r??
 */
 
-void X86FrameLowering::emitPrologue(MachineFunction &MF) const {
-  MachineBasicBlock &MBB = MF.front(); // Prologue goes in entry BB.
+void X86FrameLowering::emitPrologue(MachineFunction &MF,
+                                    MachineBasicBlock &MBB) const {
+  assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
   MachineBasicBlock::iterator MBBI = MBB.begin();
   MachineFrameInfo *MFI = MF.getFrameInfo();
   const Function *Fn = MF.getFunction();
@@ -1590,9 +1591,10 @@ GetScratchRegister(bool Is64Bit, bool IsLP64, const MachineFunction &MF, bool Pr
 // limit.
 static const uint64_t kSplitStackAvailable = 256;
 
-void
-X86FrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
-  MachineBasicBlock &prologueMBB = MF.front();
+void X86FrameLowering::adjustForSegmentedStacks(
+    MachineFunction &MF, MachineBasicBlock &PrologueMBB) const {
+  assert(&PrologueMBB == &MF.front() &&
+         "Shrink-wrapping is not implemented yet");
   MachineFrameInfo *MFI = MF.getFrameInfo();
   const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
   const TargetInstrInfo &TII = *STI.getInstrInfo();
@@ -1634,8 +1636,9 @@ X86FrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
   // The MOV R10, RAX needs to be in a different block, since the RET we emit in
   // allocMBB needs to be last (terminating) instruction.
 
-  for (MachineBasicBlock::livein_iterator i = prologueMBB.livein_begin(),
-         e = prologueMBB.livein_end(); i != e; i++) {
+  for (MachineBasicBlock::livein_iterator i = PrologueMBB.livein_begin(),
+                                          e = PrologueMBB.livein_end();
+       i != e; i++) {
     allocMBB->addLiveIn(*i);
     checkMBB->addLiveIn(*i);
   }
@@ -1749,7 +1752,7 @@ X86FrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
 
   // This jump is taken if SP >= (Stacklet Limit + Stack Space required).
   // It jumps to normal execution of the function body.
-  BuildMI(checkMBB, DL, TII.get(X86::JA_1)).addMBB(&prologueMBB);
+  BuildMI(checkMBB, DL, TII.get(X86::JA_1)).addMBB(&PrologueMBB);
 
   // On 32 bit we first push the arguments size and then the frame size. On 64
   // bit, we pass the stack frame size in r10 and the argument size in r11.
@@ -1816,10 +1819,10 @@ X86FrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
   else
     BuildMI(allocMBB, DL, TII.get(X86::MORESTACK_RET));
 
-  allocMBB->addSuccessor(&prologueMBB);
+  allocMBB->addSuccessor(&PrologueMBB);
 
   checkMBB->addSuccessor(allocMBB);
-  checkMBB->addSuccessor(&prologueMBB);
+  checkMBB->addSuccessor(&PrologueMBB);
 
 #ifdef XDEBUG
   MF.verify();
@@ -1841,7 +1844,8 @@ X86FrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
 ///       call inc_stack   # doubles the stack space
 ///       temp0 = sp - MaxStack
 ///       if( temp0 < SP_LIMIT(P) ) goto IncStack else goto OldStart
-void X86FrameLowering::adjustForHiPEPrologue(MachineFunction &MF) const {
+void X86FrameLowering::adjustForHiPEPrologue(
+    MachineFunction &MF, MachineBasicBlock &PrologueMBB) const {
   const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
   const TargetInstrInfo &TII = *STI.getInstrInfo();
   MachineFrameInfo *MFI = MF.getFrameInfo();
@@ -1910,12 +1914,14 @@ void X86FrameLowering::adjustForHiPEPrologue(MachineFunction &MF) const {
   // If the stack frame needed is larger than the guaranteed then runtime checks
   // and calls to "inc_stack_0" BIF should be inserted in the assembly prologue.
   if (MaxStack > Guaranteed) {
-    MachineBasicBlock &prologueMBB = MF.front();
+    assert(&PrologueMBB == &MF.front() &&
+           "Shrink-wrapping is not implemented yet");
     MachineBasicBlock *stackCheckMBB = MF.CreateMachineBasicBlock();
     MachineBasicBlock *incStackMBB = MF.CreateMachineBasicBlock();
 
-    for (MachineBasicBlock::livein_iterator I = prologueMBB.livein_begin(),
-           E = prologueMBB.livein_end(); I != E; I++) {
+    for (MachineBasicBlock::livein_iterator I = PrologueMBB.livein_begin(),
+                                            E = PrologueMBB.livein_end();
+         I != E; I++) {
       stackCheckMBB->addLiveIn(*I);
       incStackMBB->addLiveIn(*I);
     }
@@ -1951,7 +1957,7 @@ void X86FrameLowering::adjustForHiPEPrologue(MachineFunction &MF) const {
     // SPLimitOffset is in a fixed heap location (pointed by BP).
     addRegOffset(BuildMI(stackCheckMBB, DL, TII.get(CMPop))
                  .addReg(ScratchReg), PReg, false, SPLimitOffset);
-    BuildMI(stackCheckMBB, DL, TII.get(X86::JAE_1)).addMBB(&prologueMBB);
+    BuildMI(stackCheckMBB, DL, TII.get(X86::JAE_1)).addMBB(&PrologueMBB);
 
     // Create new MBB for IncStack:
     BuildMI(incStackMBB, DL, TII.get(CALLop)).
@@ -1962,9 +1968,9 @@ void X86FrameLowering::adjustForHiPEPrologue(MachineFunction &MF) const {
                  .addReg(ScratchReg), PReg, false, SPLimitOffset);
     BuildMI(incStackMBB, DL, TII.get(X86::JLE_1)).addMBB(incStackMBB);
 
-    stackCheckMBB->addSuccessor(&prologueMBB, 99);
+    stackCheckMBB->addSuccessor(&PrologueMBB, 99);
     stackCheckMBB->addSuccessor(incStackMBB, 1);
-    incStackMBB->addSuccessor(&prologueMBB, 99);
+    incStackMBB->addSuccessor(&PrologueMBB, 99);
     incStackMBB->addSuccessor(incStackMBB, 1);
   }
 #ifdef XDEBUG
diff --git a/llvm/lib/Target/X86/X86FrameLowering.h b/llvm/lib/Target/X86/X86FrameLowering.h
index 542bbbc79ae..a23bce9745e 100644
--- a/llvm/lib/Target/X86/X86FrameLowering.h
+++ b/llvm/lib/Target/X86/X86FrameLowering.h
@@ -35,12 +35,14 @@ public:
 
   /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
   /// the function.
-  void emitPrologue(MachineFunction &MF) const override;
+  void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
-  void adjustForSegmentedStacks(MachineFunction &MF) const override;
+  void adjustForSegmentedStacks(MachineFunction &MF,
+                                MachineBasicBlock &PrologueMBB) const override;
 
-  void adjustForHiPEPrologue(MachineFunction &MF) const override;
+  void adjustForHiPEPrologue(MachineFunction &MF,
+                             MachineBasicBlock &PrologueMBB) const override;
 
   void processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
                                      RegScavenger *RS = nullptr) const override;
diff --git a/llvm/lib/Target/XCore/XCoreFrameLowering.cpp b/llvm/lib/Target/XCore/XCoreFrameLowering.cpp
index e0ac0e56781..bd834cc5be4 100644
--- a/llvm/lib/Target/XCore/XCoreFrameLowering.cpp
+++ b/llvm/lib/Target/XCore/XCoreFrameLowering.cpp
@@ -220,8 +220,9 @@ bool XCoreFrameLowering::hasFP(const MachineFunction &MF) const {
          MF.getFrameInfo()->hasVarSizedObjects();
 }
 
-void XCoreFrameLowering::emitPrologue(MachineFunction &MF) const {
-  MachineBasicBlock &MBB = MF.front();   // Prolog goes in entry BB
+void XCoreFrameLowering::emitPrologue(MachineFunction &MF,
+                                      MachineBasicBlock &MBB) const {
+  assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
   MachineBasicBlock::iterator MBBI = MBB.begin();
   MachineFrameInfo *MFI = MF.getFrameInfo();
   MachineModuleInfo *MMI = &MF.getMMI();
diff --git a/llvm/lib/Target/XCore/XCoreFrameLowering.h b/llvm/lib/Target/XCore/XCoreFrameLowering.h
index 7b169c2b8cd..607c7724895 100644
--- a/llvm/lib/Target/XCore/XCoreFrameLowering.h
+++ b/llvm/lib/Target/XCore/XCoreFrameLowering.h
@@ -27,7 +27,8 @@ namespace llvm {
 
     /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
     /// the function.
-    void emitPrologue(MachineFunction &MF) const override;
+    void emitPrologue(MachineFunction &MF,
+                      MachineBasicBlock &MBB) const override;
     void emitEpilogue(MachineFunction &MF,
                       MachineBasicBlock &MBB) const override;