[llvm] [X86][GlobalISel] - Legalize And Select of G_FPTOSI/G_SITOFP in X87 mode (PR #137377)

[Matt Arsenault via llvm-commits]

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@@ -671,10 +690,77 @@ bool X86LegalizerInfo::legalizeCustom(LegalizerHelper &Helper, MachineInstr &MI,
     return legalizeUITOFP(MI, MRI, Helper);
   case TargetOpcode::G_STORE:
     return legalizeNarrowingStore(MI, MRI, Helper);
+  case TargetOpcode::G_SITOFP:
+    return legalizeSITOFP(MI, MRI, Helper);
+  case TargetOpcode::G_FPTOSI:
+    return legalizeFPTOSI(MI, MRI, Helper);
   }
   llvm_unreachable("expected switch to return");
 }
 
+bool X86LegalizerInfo::legalizeSITOFP(MachineInstr &MI,
+                                      MachineRegisterInfo &MRI,
+                                      LegalizerHelper &Helper) const {
+  MachineIRBuilder &MIRBuilder = Helper.MIRBuilder;
+  MachineFunction &MF = *MI.getMF();
+  auto [Dst, DstTy, Src, SrcTy] = MI.getFirst2RegLLTs();
+
+  assert((SrcTy.getSizeInBits() == 16 || SrcTy.getSizeInBits() == 32 ||
+          SrcTy.getSizeInBits() == 64) &&
+         "Unexpected source type for SITOFP in X87 mode.");
+
+  const LLT p0 = LLT::pointer(0, MF.getTarget().getPointerSizeInBits(0));
+  int MemSize = SrcTy.getSizeInBytes();
+  int StackSlot =
+      MF.getFrameInfo().CreateStackObject(MemSize, Align(MemSize), false);
+
+  auto SlotPointer = MIRBuilder.buildFrameIndex(p0, StackSlot);
+  MachinePointerInfo PtrInfo = MachinePointerInfo::getFixedStack(MF, StackSlot);
+  MachineMemOperand *StoreMMO = MF.getMachineMemOperand(
+      PtrInfo, MachineMemOperand::MOStore, MemSize, Align(MemSize));
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arsenm wrote:

Can use LegalizerHelper::createStackTemporary? 

https://github.com/llvm/llvm-project/pull/137377