[llvm] [GISEL][RISCV] Add G_VACOPY GISEL opcode and add lowering code for it. (PR #73066)

[Michael Maitland via llvm-commits]

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@@ -261,9 +268,64 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST) {
   getActionDefinitionsBuilder({G_FCEIL, G_FFLOOR})
       .libcallFor({s32, s64});
 
+  getActionDefinitionsBuilder(G_VASTART).customFor({p0});
+
+  // va_list must be a pointer, but most sized types are pretty easy to handle
+  // as the destination.
+  getActionDefinitionsBuilder(G_VAARG).lowerForCartesianProduct(
+      {s8, s16, s32, s64, p0}, {p0});
+
   getLegacyLegalizerInfo().computeTables();
 }
 
+static Type *getTypeForLLT(LLT Ty, LLVMContext &C) {
+  if (Ty.isVector())
+    return FixedVectorType::get(IntegerType::get(C, Ty.getScalarSizeInBits()),
+                                Ty.getNumElements());
+  return IntegerType::get(C, Ty.getSizeInBits());
+}
+
+#include "llvm/CodeGen/GlobalISel/GenericMachineInstrs.h"
+bool RISCVLegalizerInfo::legalizeIntrinsic(LegalizerHelper &Helper,
+                                           MachineInstr &MI) const {
+  Intrinsic::ID IntrinsicID = cast<GIntrinsic>(MI).getIntrinsicID();
+  switch (IntrinsicID) {
+  default:
+    return false;
+  case Intrinsic::vacopy: {
+    // vacopy arguments must be legal because of the intrinsic signature.
+    // No need to check here.
+
+    MachineIRBuilder &MIRBuilder = Helper.MIRBuilder;
+    MachineRegisterInfo &MRI = *MIRBuilder.getMRI();
+    MachineFunction &MF = *MI.getMF();
+    const DataLayout &DL = MIRBuilder.getDataLayout();
+    LLVMContext &Ctx = MF.getFunction().getContext();
+
+    Register DstLst = MI.getOperand(0).getReg();
+    LLT PtrTy = MRI.getType(DstLst);
+
+    // Load the source va_list
+    Align Alignment = Align(DL.getABITypeAlign(getTypeForLLT(PtrTy, Ctx)));
+    MachineMemOperand *LoadMMO =
+        MF.getMachineMemOperand(MachinePointerInfo::getUnknownStack(MF),
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michaelmaitland wrote:

It doesn't look like the IR lowering processes preserves the Value * from the IR when lowering to the intrinsic. I agree we should do this when we add G_VACOPY and let it slide for now. What do you think?

https://github.com/llvm/llvm-project/pull/73066