[COFF, ARM64] Decide when to mark struct returns as SRet

Summary:
Refer the MS ARM64 ABI Convention for the behavior for struct returns:
https://docs.microsoft.com/en-us/cpp/build/arm64-windows-abi-conventions#return-values

Reviewers: mstorsjo, compnerd, rnk, javed.absar, yinma, efriedma

Reviewed By: rnk, efriedma

Subscribers: haripul, TomTan, yinma, efriedma, kristof.beyls, chrib, llvm-commits

Differential Revision: https://reviews.llvm.org/D49464

llvm-svn: 338050

2 files changed, 14 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index f60136c2f17..f066ce16858 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -1988,7 +1988,8 @@ void CodeGenModule::ConstructAttributeList(
   // Attach attributes to sret.
   if (IRFunctionArgs.hasSRetArg()) {
     llvm::AttrBuilder SRETAttrs;
-    SRETAttrs.addAttribute(llvm::Attribute::StructRet);
+    if (!RetAI.getSuppressSRet())
+      SRETAttrs.addAttribute(llvm::Attribute::StructRet);
     hasUsedSRet = true;
     if (RetAI.getInReg())
       SRETAttrs.addAttribute(llvm::Attribute::InReg);
diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index e5e9cf67fdd..a1122dc80af 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -1060,10 +1060,22 @@ bool MicrosoftCXXABI::classifyReturnType(CGFunctionInfo &FI) const {
     // the second parameter.
     FI.getReturnInfo() = ABIArgInfo::getIndirect(Align, /*ByVal=*/false);
     FI.getReturnInfo().setSRetAfterThis(FI.isInstanceMethod());
+
+    // aarch64-windows requires that instance methods use X1 for the return
+    // address. So for aarch64-windows we do not mark the
+    // return as SRet.
+    FI.getReturnInfo().setSuppressSRet(CGM.getTarget().getTriple().getArch() ==
+                                       llvm::Triple::aarch64);
     return true;
   } else if (!RD->isPOD()) {
     // If it's a free function, non-POD types are returned indirectly.
     FI.getReturnInfo() = ABIArgInfo::getIndirect(Align, /*ByVal=*/false);
+
+    // aarch64-windows requires that non-POD, non-instance returns use X0 for
+    // the return address. So for aarch64-windows we do not mark the return as
+    // SRet.
+    FI.getReturnInfo().setSuppressSRet(CGM.getTarget().getTriple().getArch() ==
+                                       llvm::Triple::aarch64);
     return true;
   }