[clang][AMDGPU]: Don't use byval for struct arguments in function ABI

Summary:
  Byval requires allocating additional stack space, and always requires an implicit copy to be inserted in codegen,
where it can be difficult to optimize. In this work, we use byref/IndirectAliased promotion method instead of
byval with the implicit copy semantics.

Reviewers:
  arsenm

Differential Revision:
  https://reviews.llvm.org/D155986

1 files changed, 8 insertions, 4 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 28c3bc7c..2b5121a 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -2156,7 +2156,8 @@ static bool DetermineNoUndef(QualType QTy, CodeGenTypes &Types,
                              const llvm::DataLayout &DL, const ABIArgInfo &AI,
                              bool CheckCoerce = true) {
   llvm::Type *Ty = Types.ConvertTypeForMem(QTy);
-  if (AI.getKind() == ABIArgInfo::Indirect)
+  if (AI.getKind() == ABIArgInfo::Indirect ||
+      AI.getKind() == ABIArgInfo::IndirectAliased)
     return true;
   if (AI.getKind() == ABIArgInfo::Extend)
     return true;
@@ -5126,12 +5127,15 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
           auto LV = I->getKnownLValue();
           auto AS = LV.getAddressSpace();
 
-          if (!ArgInfo.getIndirectByVal() ||
+          bool isByValOrRef =
+              ArgInfo.isIndirectAliased() || ArgInfo.getIndirectByVal();
+
+          if (!isByValOrRef ||
               (LV.getAlignment() < getContext().getTypeAlignInChars(I->Ty))) {
             NeedCopy = true;
           }
           if (!getLangOpts().OpenCL) {
-            if ((ArgInfo.getIndirectByVal() &&
+            if ((isByValOrRef &&
                 (AS != LangAS::Default &&
                  AS != CGM.getASTAllocaAddressSpace()))) {
               NeedCopy = true;
@@ -5139,7 +5143,7 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
           }
           // For OpenCL even if RV is located in default or alloca address space
           // we don't want to perform address space cast for it.
-          else if ((ArgInfo.getIndirectByVal() &&
+          else if ((isByValOrRef &&
                     Addr.getType()->getAddressSpace() != IRFuncTy->
                       getParamType(FirstIRArg)->getPointerAddressSpace())) {
             NeedCopy = true;