[WebAssembly] Make clang emit correct va_arg code for structs

Summary:
In the WebAssembly backend, when lowering variadic function calls, non-single
member aggregate type arguments are always passed by pointer.

However, when emitting va_arg code in clang, the arguments are instead read as
if they are passed directly. This results in the pointer being read as the
actual structure.

Fixes https://github.com/emscripten-core/emscripten/issues/9042.

Reviewers: tlively, sbc100, kripken, aheejin, dschuff

Reviewed By: dschuff

Subscribers: dschuff, jgravelle-google, sunfish, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66168

llvm-svn: 368750

1 files changed, 4 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 884b80cecd0..d96b5408f31 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -833,10 +833,12 @@ ABIArgInfo WebAssemblyABIInfo::classifyReturnType(QualType RetTy) const {
 
 Address WebAssemblyABIInfo::EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
                                       QualType Ty) const {
-  return emitVoidPtrVAArg(CGF, VAListAddr, Ty, /*IsIndirect=*/ false,
+  bool IsIndirect =
+      isAggregateTypeForABI(Ty) && !isSingleElementStruct(Ty, getContext());
+  return emitVoidPtrVAArg(CGF, VAListAddr, Ty, IsIndirect,
                           getContext().getTypeInfoInChars(Ty),
                           CharUnits::fromQuantity(4),
-                          /*AllowHigherAlign=*/ true);
+                          /*AllowHigherAlign=*/true);
 }
 
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