1 files changed, 38 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index c5451708d1b..79297d35b0c 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -17,6 +17,7 @@
 #include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
 #include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/TargetFrameLowering.h"
 #include "llvm/CodeGen/TargetInstrInfo.h"
 #include "llvm/CodeGen/TargetLowering.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
@@ -2153,6 +2154,8 @@ LegalizerHelper::lower(MachineInstr &MI, unsigned TypeIdx, LLT Ty) {
   }
   case G_SHUFFLE_VECTOR:
     return lowerShuffleVector(MI);
+  case G_DYN_STACKALLOC:
+    return lowerDynStackAlloc(MI);
   }
 }
 
@@ -3913,3 +3916,38 @@ LegalizerHelper::lowerShuffleVector(MachineInstr &MI) {
   MI.eraseFromParent();
   return Legalized;
 }
+
+LegalizerHelper::LegalizeResult
+LegalizerHelper::lowerDynStackAlloc(MachineInstr &MI) {
+  Register Dst = MI.getOperand(0).getReg();
+  Register AllocSize = MI.getOperand(1).getReg();
+  unsigned Align = MI.getOperand(2).getImm();
+
+  const auto &MF = *MI.getMF();
+  const auto &TLI = *MF.getSubtarget().getTargetLowering();
+
+  LLT PtrTy = MRI.getType(Dst);
+  LLT IntPtrTy = LLT::scalar(PtrTy.getSizeInBits());
+
+  Register SPReg = TLI.getStackPointerRegisterToSaveRestore();
+  auto SPTmp = MIRBuilder.buildCopy(PtrTy, SPReg);
+  SPTmp = MIRBuilder.buildCast(IntPtrTy, SPTmp);
+
+  // Subtract the final alloc from the SP. We use G_PTRTOINT here so we don't
+  // have to generate an extra instruction to negate the alloc and then use
+  // G_GEP to add the negative offset.
+  auto Alloc = MIRBuilder.buildSub(IntPtrTy, SPTmp, AllocSize);
+  if (Align) {
+    APInt AlignMask(IntPtrTy.getSizeInBits(), Align, true);
+    AlignMask.negate();
+    auto AlignCst = MIRBuilder.buildConstant(IntPtrTy, AlignMask);
+    Alloc = MIRBuilder.buildAnd(IntPtrTy, Alloc, AlignCst);
+  }
+
+  SPTmp = MIRBuilder.buildCast(PtrTy, Alloc);
+  MIRBuilder.buildCopy(SPReg, SPTmp);
+  MIRBuilder.buildCopy(Dst, SPTmp);
+
+  MI.eraseFromParent();
+  return Legalized;
+}