Add a local stack object block allocation pass. This is still an

experimental pass that allocates locals relative to one another before
register allocation and then assigns them to actual stack slots as a block
later in PEI. This will eventually allow targets with limited index offset
range to allocate additional base registers (not just FP and SP) to
more efficiently reference locals, as well as handle situations where
locals cannot be referenced via SP or FP at all (dynamic stack realignment
together with variable sized objects, for example). It's currently
incomplete and almost certainly buggy. Work in progress.

Disabled by default and gated via the -enable-local-stack-alloc command
line option.

rdar://8277890

llvm-svn: 111059

1 files changed, 32 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
index cba92fad12b..8f1d3a6da61 100644
--- a/llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -19,6 +19,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#define DEBUG_TYPE "pei"
 #include "PrologEpilogInserter.h"
 #include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/MachineLoopInfo.h"
@@ -32,6 +33,7 @@
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
 #include "llvm/ADT/IndexedMap.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/STLExtras.h"
@@ -39,6 +41,10 @@
 
 using namespace llvm;
 
+// FIXME: For testing purposes only. Remove once the pre-allocation pass
+// is done.
+extern cl::opt<bool> EnableLocalStackAlloc;
+
 char PEI::ID = 0;
 
 INITIALIZE_PASS(PEI, "prologepilog",
@@ -462,8 +468,10 @@ AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx,
   Offset = (Offset + Align - 1) / Align * Align;
 
   if (StackGrowsDown) {
+    DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset << "]\n");
     MFI->setObjectOffset(FrameIdx, -Offset); // Set the computed offset
   } else {
+    DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << Offset << "]\n");
     MFI->setObjectOffset(FrameIdx, Offset);
     Offset += MFI->getObjectSize(FrameIdx);
   }
@@ -548,6 +556,26 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
       AdjustStackOffset(MFI, SFI, StackGrowsDown, Offset, MaxAlign);
   }
 
+  // Store the offset of the start of the local allocation block. This
+  // will be used later when resolving frame base virtual register pseudos.
+  MFI->setLocalFrameBaseOffset(Offset);
+  if (EnableLocalStackAlloc) {
+    // Allocate the local block
+    Offset += MFI->getLocalFrameSize();
+
+    // Resolve offsets for objects in the local block.
+    for (unsigned i = 0, e = MFI->getLocalFrameObjectCount(); i != e; ++i) {
+      std::pair<int, int64_t> Entry = MFI->getLocalFrameObjectMap(i);
+      int64_t FIOffset = MFI->getLocalFrameBaseOffset() + Entry.second;
+
+      AdjustStackOffset(MFI, Entry.first, StackGrowsDown, FIOffset, MaxAlign);
+    }
+  }
+  // FIXME: Allocate locals. Once the block allocation pass is turned on,
+  // this simplifies to just the second loop, since all of the large objects
+  // will have already been handled. The second loop can also simplify a
+  // bit, as the conditionals inside aren't all necessary.
+
   // Make sure that the stack protector comes before the local variables on the
   // stack.
   SmallSet<int, 16> LargeStackObjs;
@@ -557,6 +585,8 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
 
     // Assign large stack objects first.
     for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
+      if (MFI->isObjectPreAllocated(i))
+        continue;
       if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
         continue;
       if (RS && (int)i == RS->getScavengingFrameIndex())
@@ -576,6 +606,8 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
   // Then assign frame offsets to stack objects that are not used to spill
   // callee saved registers.
   for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
+    if (MFI->isObjectPreAllocated(i))
+      continue;
     if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
       continue;
     if (RS && (int)i == RS->getScavengingFrameIndex())