[clang] [clang] Fix UEFI Target info (PR #127290)

[Petr Hosek via cfe-commits]

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@@ -3038,8 +3038,30 @@ static Address EmitX86_64VAArgFromMemory(CodeGenFunction &CGF,
   return Address(Res, LTy, Align);
 }
 
+static RValue EmitMSABIVAArg(CodeGenFunction &CGF, Address VAListAddr,
+                             QualType Ty, AggValueSlot Slot,
+                             ASTContext &context) {
+  // MS x64 ABI requirement: "Any argument that doesn't fit in 8 bytes, or is
+  // not 1, 2, 4, or 8 bytes, must be passed by reference."
+  uint64_t Width = context.getTypeSize(Ty);
+  bool IsIndirect = Width > 64 || !llvm::isPowerOf2_64(Width);
+
+  return emitVoidPtrVAArg(CGF, VAListAddr, Ty, IsIndirect,
+                          CGF.getContext().getTypeInfoInChars(Ty),
+                          CharUnits::fromQuantity(8),
+                          /*allowHigherAlign*/ false, Slot);
+}
+
 RValue X86_64ABIInfo::EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
                                 QualType Ty, AggValueSlot Slot) const {
+
+  // Emit MS ABI compliant va_list for X86_64 targets which use Microsoft CXX
+  // ABI and CharPtrBuiltinVaList.
+  if (CGF.getTarget().getCXXABI().isMicrosoft() &&
+      CGF.getTarget().getBuiltinVaListKind() ==
+          clang::TargetInfo::CharPtrBuiltinVaList)
+    return EmitMSABIVAArg(CGF, VAListAddr, Ty, Slot, getContext());
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petrhosek wrote:

Wouldn't it be cleaner and safer to use `WinX86_64ABIInfo` (and `WinX86_64TargetCodeGenInfo`) for UEFI?

https://github.com/llvm/llvm-project/pull/127290