[mips] Add support for dynamic stack realignment.

Summary:
With this change we are able to realign the stack dynamically, whenever it
contains objects with alignment requirements that are larger than the
alignment specified from the given ABI.

We have to use the $fp register as the frame pointer when we perform
dynamic stack realignment. In complex stack frames, with variably-sized
objects, we reserve additionally the callee-saved register $s7 as the
base pointer in order to reference locals.

Reviewers: dsanders

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8633

llvm-svn: 238829

8 files changed, 141 insertions, 8 deletions

diff --git a/llvm/lib/Target/Mips/MCTargetDesc/MipsABIInfo.cpp b/llvm/lib/Target/Mips/MCTargetDesc/MipsABIInfo.cpp
index b1f7c2f2259..bf8f7d12880 100644
--- a/llvm/lib/Target/Mips/MCTargetDesc/MipsABIInfo.cpp
+++ b/llvm/lib/Target/Mips/MCTargetDesc/MipsABIInfo.cpp
@@ -99,6 +99,10 @@ unsigned MipsABIInfo::GetFramePtr() const {
   return ArePtrs64bit() ? Mips::FP_64 : Mips::FP;
 }
 
+unsigned MipsABIInfo::GetBasePtr() const {
+  return ArePtrs64bit() ? Mips::S7_64 : Mips::S7;
+}
+
 unsigned MipsABIInfo::GetNullPtr() const {
   return ArePtrs64bit() ? Mips::ZERO_64 : Mips::ZERO;
 }
diff --git a/llvm/lib/Target/Mips/MCTargetDesc/MipsABIInfo.h b/llvm/lib/Target/Mips/MCTargetDesc/MipsABIInfo.h
index 9a6ba946765..d20dc903795 100644
--- a/llvm/lib/Target/Mips/MCTargetDesc/MipsABIInfo.h
+++ b/llvm/lib/Target/Mips/MCTargetDesc/MipsABIInfo.h
@@ -65,6 +65,7 @@ public:
 
   unsigned GetStackPtr() const;
   unsigned GetFramePtr() const;
+  unsigned GetBasePtr() const;
   unsigned GetNullPtr() const;
   unsigned GetPtrAdduOp() const;
   unsigned GetPtrAddiuOp() const;
diff --git a/llvm/lib/Target/Mips/MipsFrameLowering.cpp b/llvm/lib/Target/Mips/MipsFrameLowering.cpp
index 826fbaf4d00..a74c8abd2e2 100644
--- a/llvm/lib/Target/Mips/MipsFrameLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsFrameLowering.cpp
@@ -90,12 +90,23 @@ const MipsFrameLowering *MipsFrameLowering::create(const MipsSubtarget &ST) {
 }
 
 // hasFP - Return true if the specified function should have a dedicated frame
-// pointer register.  This is true if the function has variable sized allocas or
-// if frame pointer elimination is disabled.
+// pointer register.  This is true if the function has variable sized allocas,
+// if it needs dynamic stack realignment, if frame pointer elimination is
+// disabled, or if the frame address is taken.
 bool MipsFrameLowering::hasFP(const MachineFunction &MF) const {
   const MachineFrameInfo *MFI = MF.getFrameInfo();
+  const TargetRegisterInfo *TRI = STI.getRegisterInfo();
+
   return MF.getTarget().Options.DisableFramePointerElim(MF) ||
-      MFI->hasVarSizedObjects() || MFI->isFrameAddressTaken();
+      MFI->hasVarSizedObjects() || MFI->isFrameAddressTaken() ||
+      TRI->needsStackRealignment(MF);
+}
+
+bool MipsFrameLowering::hasBP(const MachineFunction &MF) const {
+  const MachineFrameInfo *MFI = MF.getFrameInfo();
+  const TargetRegisterInfo *TRI = STI.getRegisterInfo();
+
+  return MFI->hasVarSizedObjects() && TRI->needsStackRealignment(MF);
 }
 
 uint64_t MipsFrameLowering::estimateStackSize(const MachineFunction &MF) const {
diff --git a/llvm/lib/Target/Mips/MipsFrameLowering.h b/llvm/lib/Target/Mips/MipsFrameLowering.h
index 0b5183081e0..5eabd58e868 100644
--- a/llvm/lib/Target/Mips/MipsFrameLowering.h
+++ b/llvm/lib/Target/Mips/MipsFrameLowering.h
@@ -32,6 +32,8 @@ public:
 
   bool hasFP(const MachineFunction &MF) const override;
 
+  bool hasBP(const MachineFunction &MF) const;
+
   bool isFPCloseToIncomingSP() const override { return false; }
 
   void
diff --git a/llvm/lib/Target/Mips/MipsRegisterInfo.cpp b/llvm/lib/Target/Mips/MipsRegisterInfo.cpp
index f72fb4d622e..f6647e6a846 100644
--- a/llvm/lib/Target/Mips/MipsRegisterInfo.cpp
+++ b/llvm/lib/Target/Mips/MipsRegisterInfo.cpp
@@ -21,6 +21,7 @@
 #include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/IR/Constants.h"
@@ -178,6 +179,15 @@ getReservedRegs(const MachineFunction &MF) const {
     else {
       Reserved.set(Mips::FP);
       Reserved.set(Mips::FP_64);
+
+      // Reserve the base register if we need to both realign the stack and
+      // allocate variable-sized objects at runtime. This should test the
+      // same conditions as MipsFrameLowering::hasBP().
+      if (needsStackRealignment(MF) &&
+          MF.getFrameInfo()->hasVarSizedObjects()) {
+        Reserved.set(Mips::S7);
+        Reserved.set(Mips::S7_64);
+      }
     }
   }
 
@@ -271,6 +281,67 @@ getFrameRegister(const MachineFunction &MF) const {
   else
     return TFI->hasFP(MF) ? (IsN64 ? Mips::FP_64 : Mips::FP) :
                             (IsN64 ? Mips::SP_64 : Mips::SP);
+}
 
+bool MipsRegisterInfo::canRealignStack(const MachineFunction &MF) const {
+  const MipsSubtarget &Subtarget = MF.getSubtarget<MipsSubtarget>();
+  unsigned FP = Subtarget.isGP32bit() ? Mips::FP : Mips::FP_64;
+  unsigned BP = Subtarget.isGP32bit() ? Mips::S7 : Mips::S7_64;
+
+  // Support dynamic stack realignment only for targets with standard encoding.
+  if (!Subtarget.hasStandardEncoding())
+    return false;
+
+  // We can't perform dynamic stack realignment if we can't reserve the
+  // frame pointer register.
+  if (!MF.getRegInfo().canReserveReg(FP))
+    return false;
+
+  // We can realign the stack if we know the maximum call frame size and we
+  // don't have variable sized objects.
+  if (Subtarget.getFrameLowering()->hasReservedCallFrame(MF))
+    return true;
+
+  // We have to reserve the base pointer register in the presence of variable
+  // sized objects.
+  return MF.getRegInfo().canReserveReg(BP);
 }
 
+bool MipsRegisterInfo::needsStackRealignment(const MachineFunction &MF) const {
+  const MipsSubtarget &Subtarget = MF.getSubtarget<MipsSubtarget>();
+  const MachineFrameInfo *MFI = MF.getFrameInfo();
+
+  bool CanRealign = canRealignStack(MF);
+
+  // Avoid realigning functions that explicitly do not want to be realigned.
+  // Normally, we should report an error when a function should be dynamically
+  // realigned but also has the attribute no-realign-stack. Unfortunately,
+  // with this attribute, MachineFrameInfo clamps each new object's alignment
+  // to that of the stack's alignment as specified by the ABI. As a result,
+  // the information of whether we have objects with larger alignment
+  // requirement than the stack's alignment is already lost at this point.
+  if (MF.getFunction()->hasFnAttribute("no-realign-stack"))
+    return false;
+
+  const Function *F = MF.getFunction();
+  if (F->hasFnAttribute(Attribute::StackAlignment)) {
+#ifdef DEBUG
+    if (!CanRealign)
+      DEBUG(dbgs() << "It's not possible to realign the stack of the function: "
+            << F->getName() << "\n");
+#endif
+    return CanRealign;
+  }
+
+  unsigned StackAlignment = Subtarget.getFrameLowering()->getStackAlignment();
+  if (MFI->getMaxAlignment() > StackAlignment) {
+#ifdef DEBUG
+    if (!CanRealign)
+      DEBUG(dbgs() << "It's not possible to realign the stack of the function: "
+            << F->getName() << "\n");
+#endif
+    return CanRealign;
+  }
+
+  return false;
+}
diff --git a/llvm/lib/Target/Mips/MipsRegisterInfo.h b/llvm/lib/Target/Mips/MipsRegisterInfo.h
index 76e84bd142b..ee1f6bcd739 100644
--- a/llvm/lib/Target/Mips/MipsRegisterInfo.h
+++ b/llvm/lib/Target/Mips/MipsRegisterInfo.h
@@ -57,6 +57,14 @@ public:
                            int SPAdj, unsigned FIOperandNum,
                            RegScavenger *RS = nullptr) const override;
 
+  void processFunctionBeforeFrameFinalized(MachineFunction &MF,
+                                       RegScavenger *RS = nullptr) const;
+
+  // Stack realignment queries.
+  bool canRealignStack(const MachineFunction &MF) const;
+
+  bool needsStackRealignment(const MachineFunction &MF) const override;
+
   /// Debug information queries.
   unsigned getFrameRegister(const MachineFunction &MF) const override;
 
diff --git a/llvm/lib/Target/Mips/MipsSEFrameLowering.cpp b/llvm/lib/Target/Mips/MipsSEFrameLowering.cpp
index 19efa59e1fd..ec7bf314c64 100644
--- a/llvm/lib/Target/Mips/MipsSEFrameLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsSEFrameLowering.cpp
@@ -382,6 +382,11 @@ void MipsSEFrameLowering::emitPrologue(MachineFunction &MF,
   unsigned FP = ABI.GetFramePtr();
   unsigned ZERO = ABI.GetNullPtr();
   unsigned ADDu = ABI.GetPtrAdduOp();
+  unsigned ADDiu = ABI.GetPtrAddiuOp();
+  unsigned AND = ABI.IsN64() ? Mips::AND64 : Mips::AND;
+
+  const TargetRegisterClass *RC = ABI.ArePtrs64bit() ?
+        &Mips::GPR64RegClass : &Mips::GPR32RegClass;
 
   // First, compute final stack size.
   uint64_t StackSize = MFI->getStackSize();
@@ -464,15 +469,12 @@ void MipsSEFrameLowering::emitPrologue(MachineFunction &MF,
   }
 
   if (MipsFI->callsEhReturn()) {
-    const TargetRegisterClass *PtrRC =
-        ABI.ArePtrs64bit() ? &Mips::GPR64RegClass : &Mips::GPR32RegClass;
-
     // Insert instructions that spill eh data registers.
     for (int I = 0; I < 4; ++I) {
       if (!MBB.isLiveIn(ABI.GetEhDataReg(I)))
         MBB.addLiveIn(ABI.GetEhDataReg(I));
       TII.storeRegToStackSlot(MBB, MBBI, ABI.GetEhDataReg(I), false,
-                              MipsFI->getEhDataRegFI(I), PtrRC, &RegInfo);
+                              MipsFI->getEhDataRegFI(I), RC, &RegInfo);
     }
 
     // Emit .cfi_offset directives for eh data registers.
@@ -497,6 +499,26 @@ void MipsSEFrameLowering::emitPrologue(MachineFunction &MF,
         nullptr, MRI->getDwarfRegNum(FP, true)));
     BuildMI(MBB, MBBI, dl, TII.get(TargetOpcode::CFI_INSTRUCTION))
         .addCFIIndex(CFIIndex);
+
+    if (RegInfo.needsStackRealignment(MF)) {
+      // addiu $Reg, $zero, -MaxAlignment
+      // andi $sp, $sp, $Reg
+      unsigned VR = MF.getRegInfo().createVirtualRegister(RC);
+      assert(isInt<16>(MFI->getMaxAlignment()) &&
+             "Function's alignment size requirement is not supported.");
+      int MaxAlign = - (signed) MFI->getMaxAlignment();
+
+      BuildMI(MBB, MBBI, dl, TII.get(ADDiu), VR).addReg(ZERO) .addImm(MaxAlign);
+      BuildMI(MBB, MBBI, dl, TII.get(AND), SP).addReg(SP).addReg(VR);
+
+      if (hasBP(MF)) {
+        // move $s7, $sp
+        unsigned BP = STI.isABI_N64() ? Mips::S7_64 : Mips::S7;
+        BuildMI(MBB, MBBI, dl, TII.get(ADDu), BP)
+          .addReg(SP)
+          .addReg(ZERO);
+      }
+    }
   }
 }
 
@@ -606,10 +628,14 @@ processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
   MipsFunctionInfo *MipsFI = MF.getInfo<MipsFunctionInfo>();
   MipsABIInfo ABI = STI.getABI();
   unsigned FP = ABI.GetFramePtr();
+  unsigned BP = ABI.IsN64() ? Mips::S7_64 : Mips::S7;
 
   // Mark $fp as used if function has dedicated frame pointer.
   if (hasFP(MF))
     MRI.setPhysRegUsed(FP);
+  // Mark $s7 as used if function has dedicated base pointer.
+  if (hasBP(MF))
+    MRI.setPhysRegUsed(BP);
 
   // Create spill slots for eh data registers if function calls eh_return.
   if (MipsFI->callsEhReturn())
diff --git a/llvm/lib/Target/Mips/MipsSERegisterInfo.cpp b/llvm/lib/Target/Mips/MipsSERegisterInfo.cpp
index 8c74a98ecca..132c3a1001a 100644
--- a/llvm/lib/Target/Mips/MipsSERegisterInfo.cpp
+++ b/llvm/lib/Target/Mips/MipsSERegisterInfo.cpp
@@ -110,8 +110,11 @@ void MipsSERegisterInfo::eliminateFI(MachineBasicBlock::iterator II,
   MachineFunction &MF = *MI.getParent()->getParent();
   MachineFrameInfo *MFI = MF.getFrameInfo();
   MipsFunctionInfo *MipsFI = MF.getInfo<MipsFunctionInfo>();
+
   MipsABIInfo ABI =
       static_cast<const MipsTargetMachine &>(MF.getTarget()).getABI();
+  const MipsRegisterInfo *RegInfo =
+    static_cast<const MipsRegisterInfo *>(MF.getSubtarget().getRegisterInfo());
 
   const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo();
   int MinCSFI = 0;
@@ -135,7 +138,14 @@ void MipsSERegisterInfo::eliminateFI(MachineBasicBlock::iterator II,
 
   if ((FrameIndex >= MinCSFI && FrameIndex <= MaxCSFI) || EhDataRegFI)
     FrameReg = ABI.GetStackPtr();
-  else
+  else if (RegInfo->needsStackRealignment(MF)) {
+    if (MFI->hasVarSizedObjects() && !MFI->isFixedObjectIndex(FrameIndex))
+      FrameReg = ABI.GetBasePtr();
+    else if (MFI->isFixedObjectIndex(FrameIndex))
+      FrameReg = getFrameRegister(MF);
+    else
+      FrameReg = ABI.GetStackPtr();
+  } else
     FrameReg = getFrameRegister(MF);
 
   // Calculate final offset.