[SystemZ] Fix some ABI corner cases

Running the GCC's inter-compiler ABI compatibility test suite uncovered
a couple of errors in clang's SystemZ ABI implementation.  These all
affect only rare corner cases:

- Short vector types

GCC synthetic vector types defined with __attribute__ ((vector_size ...))
are always passed and returned by reference.  (This is not documented in
the official ABI document, but is the de-facto ABI implemented by GCC.)
clang would do that only for vector sizes >= 16 bytes, but not for shorter
vector types.

- Float-like aggregates and empty bitfields

clang would consider any aggregate containing an empty bitfield as
first element to be a float-like aggregate.  That's obviously wrong.
According to the ABI doc, the presence of an empty bitfield makes
an aggregate to be *not* float-like.  However, due to a bug in GCC,
empty bitfields are ignored in C++; this patch changes clang to be
compatible with this "feature" of GCC.

- Float-like aggregates and va_arg

The va_arg implementation would mis-detect some aggregates as float-like
that aren't actually passed as such.  This applies to aggregates that
have only a single element of type float or double, but using an aligned
attribute that increases the total struct size to more than 8 bytes.

This error occurred because the va_arg implement used to have an copy
of the float-like aggregate detection logic (i.e. it would call the
isFPArgumentType routine, but not perform the size check).

To simplify the logic, this patch removes the duplicated logic and
instead simply checks the (possibly coerced) LLVM argument type as
already determined by classifyArgumentType.

llvm-svn: 233543

1 files changed, 15 insertions, 8 deletions

diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 988b8fc80d2..081895f1e9a 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -5169,7 +5169,9 @@ bool SystemZABIInfo::isPromotableIntegerType(QualType Ty) const {
 }
 
 bool SystemZABIInfo::isCompoundType(QualType Ty) const {
-  return Ty->isAnyComplexType() || isAggregateTypeForABI(Ty);
+  return (Ty->isAnyComplexType() ||
+          Ty->isVectorType() ||
+          isAggregateTypeForABI(Ty));
 }
 
 bool SystemZABIInfo::isFPArgumentType(QualType Ty) const {
@@ -5204,11 +5206,12 @@ bool SystemZABIInfo::isFPArgumentType(QualType Ty) const {
 
     // Check the fields.
     for (const auto *FD : RD->fields()) {
-      // Empty bitfields don't affect things either way.
+      // For compatibility with GCC, ignore empty bitfields in C++ mode.
       // Unlike isSingleElementStruct(), empty structure and array fields
       // do count.  So do anonymous bitfields that aren't zero-sized.
-      if (FD->isBitField() && FD->getBitWidthValue(getContext()) == 0)
-        return true;
+      if (getContext().getLangOpts().CPlusPlus &&
+          FD->isBitField() && FD->getBitWidthValue(getContext()) == 0)
+        continue;
 
       // Unlike isSingleElementStruct(), arrays do not count.
       // Nested isFPArgumentType structures still do though.
@@ -5240,17 +5243,21 @@ llvm::Value *SystemZABIInfo::EmitVAArg(llvm::Value *VAListAddr, QualType Ty,
   // Every argument occupies 8 bytes and is passed by preference in either
   // GPRs or FPRs.
   Ty = CGF.getContext().getCanonicalType(Ty);
+  llvm::Type *ArgTy = CGF.ConvertTypeForMem(Ty);
+  llvm::Type *APTy = llvm::PointerType::getUnqual(ArgTy);
   ABIArgInfo AI = classifyArgumentType(Ty);
-  bool InFPRs = isFPArgumentType(Ty);
-
-  llvm::Type *APTy = llvm::PointerType::getUnqual(CGF.ConvertTypeForMem(Ty));
   bool IsIndirect = AI.isIndirect();
+  bool InFPRs = false;
   unsigned UnpaddedBitSize;
   if (IsIndirect) {
     APTy = llvm::PointerType::getUnqual(APTy);
     UnpaddedBitSize = 64;
-  } else
+  } else {
+    if (AI.getCoerceToType())
+      ArgTy = AI.getCoerceToType();
+    InFPRs = ArgTy->isFloatTy() || ArgTy->isDoubleTy();
     UnpaddedBitSize = getContext().getTypeSize(Ty);
+  }
   unsigned PaddedBitSize = 64;
   assert((UnpaddedBitSize <= PaddedBitSize) && "Invalid argument size.");