Fix for #31362 - ms_abi is implemented incorrectly for larger values (>=16 bytes).

[belickim]

Summary

This patch is a fix for following issue: https://bugs.llvm.org/show_bug.cgi?id=31362
The problem was caused by front end lowering C calling conventions without taking into account calling conventions enforced by attribute. In this case win64cc was no correctly lowered on targets other than Windows.

[rnk]

lgtm

These ABIInfo classes don't have any state, so just building one on the stack as needed is the way to go. Thanks for the fix!

[dim]

FWIW, this allows me to build wine again for x86_64, without any crashes or assertions. So that looks good, in any case.

lib/CodeGen/TargetInfo.cpp

ABIArgInfo X86_64ABIInfo::classifyRegCallStructType(QualType Ty,
   NeededInt = 0;
   NeededSSE = 0;
 
   return classifyRegCallStructTypeImpl(Ty, NeededInt, NeededSSE);
 }
 
 void X86_64ABIInfo::computeInfo(CGFunctionInfo &FI) const {
 
-  bool IsRegCall = FI.getCallingConvention() == llvm::CallingConv::X86_RegCall;
+  const unsigned CallingConv = FI.getCallingConvention();
+  // It is possible to force Win64 calling convention on any x86_64 target by
+  // using __attribute__((ms_abi)). In such case to correctly emit Win64
+  // compatible code delegate this call to WinX86_64ABIInfo::computeInfo.
+  if (CallingConv == llvm::CallingConv::Win64) {
+    WinX86_64ABIInfo Win64ABIInfo(CGT);
+    Win64ABIInfo.computeInfo(FI);
+    return;
+  }
+
+  bool IsRegCall = CallingConv == llvm::CallingConv::X86_RegCall;
 
   // Keep track of the number of assigned registers.
   unsigned FreeIntRegs = IsRegCall ? 11 : 6;
   unsigned FreeSSERegs = IsRegCall ? 16 : 8;
   unsigned NeededInt, NeededSSE;
 
   if (!getCXXABI().classifyReturnType(FI)) {
     if (IsRegCall && FI.getReturnType()->getTypePtr()->isRecordType() &&

test/CodeGen/ms_abi.c

void __attribute__((sysv_abi)) f6(__builtin_ms_va_list ap) {
   // WIN64-NEXT: bitcast i8* %[[AP_CUR3]] to %[[STRUCT_FOO]]*
   __builtin_ms_va_list ap2;
   __builtin_ms_va_copy(ap2, ap);
   // FREEBSD: %[[AP_VAL:.*]] = load i8*, i8** %[[AP]]
   // FREEBSD-NEXT: store i8* %[[AP_VAL]], i8** %[[AP2:.*]]
   // WIN64: %[[AP_VAL:.*]] = load i8*, i8** %[[AP]]
   // WIN64-NEXT: store i8* %[[AP_VAL]], i8** %[[AP2:.*]]
 }
+
+// This test checks if structs are passed according to Win64 calling convention
+// when it's enforced by __attribute((ms_abi)).
+struct i128 {
+  unsigned long long a;
+  unsigned long long b;
+};
+
+__attribute__((ms_abi)) struct i128 f7(struct i128 a) {
+  // WIN64: define void @f7(%struct.i128* noalias sret %agg.result, %struct.i128* %a)
+  // FREEBSD: define win64cc void @f7(%struct.i128* noalias sret %agg.result, %struct.i128* %a)
+  return a;
+}