[PATCH] x86-64 ABI: unwrap single element structs / arrays of 256-bit vectors to pass and return in registers

[Sanjay Patel]

Hi hfinkel, bruno,

This is a patch for PR22563 ( http://llvm.org/bugs/show_bug.cgi?id=22563 ).

We were not correctly unwrapping a single 256-bit AVX vector that was defined as an array of 1 inside a struct. 

We would generate a <4 x float> param/return value instead of <8 x float> and lose half of the vector.

http://reviews.llvm.org/D7614

Files:
  lib/CodeGen/TargetInfo.cpp
  test/CodeGen/x86_64-arguments.c

Index: lib/CodeGen/TargetInfo.cpp
===================================================================
--- lib/CodeGen/TargetInfo.cpp
+++ lib/CodeGen/TargetInfo.cpp
@@ -2179,19 +2179,15 @@
   return ABIArgInfo::getIndirect(Align);
 }
 
-/// GetByteVectorType - The ABI specifies that a value should be passed in an
-/// full vector XMM/YMM register.  Pick an LLVM IR type that will be passed as a
-/// vector register.
+/// The ABI specifies that a value should be passed in a full vector XMM/YMM
+/// register. Pick an LLVM IR type that will be passed as a vector register.
 llvm::Type *X86_64ABIInfo::GetByteVectorType(QualType Ty) const {
-  llvm::Type *IRType = CGT.ConvertType(Ty);
+  // Wrapper structs/arrays that only contain vectors are passed just like
+  // vectors; strip them off if present.
+  if (const Type *InnerTy = isSingleElementStruct(Ty, getContext()))
+    Ty = QualType(InnerTy, 0);
 
-  // Wrapper structs that just contain vectors are passed just like vectors,
-  // strip them off if present.
-  llvm::StructType *STy = dyn_cast<llvm::StructType>(IRType);
-  while (STy && STy->getNumElements() == 1) {
-    IRType = STy->getElementType(0);
-    STy = dyn_cast<llvm::StructType>(IRType);
-  }
+  llvm::Type *IRType = CGT.ConvertType(Ty);
 
   // If the preferred type is a 16-byte vector, prefer to pass it.
   if (llvm::VectorType *VT = dyn_cast<llvm::VectorType>(IRType)){
Index: test/CodeGen/x86_64-arguments.c
===================================================================
--- test/CodeGen/x86_64-arguments.c
+++ test/CodeGen/x86_64-arguments.c
@@ -184,6 +184,28 @@
   return X;
 }
 
+// PR22563 - We should unwrap simple structs and arrays to pass
+// and return them in the appropriate vector registers if possible.
+
+typedef float v8f32 __attribute__((__vector_size__(32)));
+struct v8f32wrapper {
+  v8f32 v;
+};
+
+struct v8f32wrapper f27a(struct v8f32wrapper X) {
+  // AVX-LABEL: define <8 x float> @f27a(<8 x float> %X.coerce)
+  return X;
+}
+
+struct v8f32wrapper_wrapper {
+  v8f32 v[1];
+};
+
+struct v8f32wrapper_wrapper f27b(struct v8f32wrapper_wrapper X) {
+  // AVX-LABEL: define <8 x float> @f27b(<8 x float> %X.coerce)
+  return X;
+}
+
 // rdar://5711709
 struct f28c {
   double x;

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