[ARM] Allow passing/returning of __fp16 arguments

The ACLE (ARM C Language Extensions) 2.0 allows the __fp16 type to be
used as a functon argument or return type (ACLE 1.1 did not).

The current public release of the AAPCS (2.09) states that __fp16 values
should be converted to single-precision before being passed or returned,
but AAPCS 2.10 (to be released shortly) changes this, so that they are
passed in the least-significant 16 bits of either a GPR (for base AAPCS)
or a single-precision register (for AAPCS-VFP). This does not change how
arguments are passed if they get passed on the stack.

This patch brings clang up to compliance with the latest versions of
both of these specs.

We can now set the __ARM_FP16_ARGS ACLE predefine, and we have always
been able to set the __ARM_FP16_FORMAT_IEEE predefine (we do not support
the alternative format).

llvm-svn: 246755

1 files changed, 18 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index e97b33a54e8..76998c1da1a 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -4714,6 +4714,15 @@ ABIArgInfo ARMABIInfo::classifyArgumentType(QualType Ty,
     return ABIArgInfo::getIndirect(0, /*ByVal=*/false);
   }
 
+  // __fp16 gets passed as if it were an int or float, but with the top 16 bits
+  // unspecified.
+  if (Ty->isHalfType()) {
+    llvm::Type *ResType = IsEffectivelyAAPCS_VFP ?
+      llvm::Type::getFloatTy(getVMContext()) :
+      llvm::Type::getInt32Ty(getVMContext());
+    return ABIArgInfo::getDirect(ResType);
+  }
+
   if (!isAggregateTypeForABI(Ty)) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = Ty->getAs<EnumType>()) {
@@ -4872,6 +4881,15 @@ ABIArgInfo ARMABIInfo::classifyReturnType(QualType RetTy,
     return ABIArgInfo::getIndirect(0);
   }
 
+  // __fp16 gets returned as if it were an int or float, but with the top 16
+  // bits unspecified.
+  if (RetTy->isHalfType()) {
+    llvm::Type *ResType = IsEffectivelyAAPCS_VFP ?
+      llvm::Type::getFloatTy(getVMContext()) :
+      llvm::Type::getInt32Ty(getVMContext());
+    return ABIArgInfo::getDirect(ResType);
+  }
+
   if (!isAggregateTypeForABI(RetTy)) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = RetTy->getAs<EnumType>())