MS ABI: Fix __fastcall methods that return structs

The sret paramater consumes the register after the implicit 'this'
parameter, as with other calling conventions.

Fixes PR20278, which turned out to be very easy.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212669 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/TargetInfo.cpp b/lib/CodeGen/TargetInfo.cpp
index 44e001ceb6dcb97ec4a6b5edb09cde134614c6a4..be2d5b38c6154e6e47456f019b3f33c4bb6b65a0 100644 (file)
--- a/lib/CodeGen/TargetInfo.cpp
+++ b/lib/CodeGen/TargetInfo.cpp
@@ -957,8 +957,16 @@ void X86_32ABIInfo::computeInfo(CGFunctionInfo &FI) const {
   else
     State.FreeRegs = DefaultNumRegisterParameters;
 
-  if (!getCXXABI().classifyReturnType(FI))
+  if (!getCXXABI().classifyReturnType(FI)) {
     FI.getReturnInfo() = classifyReturnType(FI.getReturnType(), State);
+  } else if (FI.getReturnInfo().isIndirect()) {
+    // The C++ ABI is not aware of register usage, so we have to check if the
+    // return value was sret and put it in a register ourselves if appropriate.
+    if (State.FreeRegs) {
+      --State.FreeRegs;  // The sret parameter consumes a register.
+      FI.getReturnInfo().setInReg(true);
+    }
+  }
 
   bool UsedInAlloca = false;
   for (auto &I : FI.arguments()) {

diff --git a/test/CodeGenCXX/microsoft-abi-cdecl-method-sret.cpp b/test/CodeGenCXX/microsoft-abi-cdecl-method-sret.cpp
index 2f8a66ea8e8778d4d521f3512da9ec05fc94d483..da58c461dcc09c1220de083c7105c8989ee4e395 100644 (file)
--- a/test/CodeGenCXX/microsoft-abi-cdecl-method-sret.cpp
+++ b/test/CodeGenCXX/microsoft-abi-cdecl-method-sret.cpp
@@ -33,3 +33,12 @@ int main() {
 // CHECK: call void {{.*}} @"\01?variadic_sret@C@@QAA?AUS@@PBDZZ"
 // CHECK: call void @"\01?cdecl_sret@C@@QAA?AUS@@XZ"
 // CHECK: call void @"\01?byval_and_sret@C@@QAA?AUS@@U2@@Z"
+
+// __fastcall has similar issues.
+struct A {
+  S __fastcall f(int x);
+};
+S A::f(int x) {
+  return S();
+}
+// CHECK-LABEL: define x86_fastcallcc void @"\01?f@A@@QAI?AUS@@H@Z"(%struct.A* inreg %this, %struct.S* inreg noalias sret %agg.result, i32 %x)