[FastISel][X86] Use getTypeForExtReturn in GetReturnInfo. (#80803)

The comment and code here seems to match getTypeForExtReturn. The
history shows that at the time this code was added, similar code existed
in SelectionDAGBuilder. SelectionDAGBuiler code has since been
refactored into getTypeForExtReturn.

This patch makes FastISel match SelectionDAGBuilder.

The test changes are because X86 has customization of
getTypeForExtReturn. So now we only extend returns to i8.

Stumbled onto this difference by accident.

1 files changed, 2 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringBase.cpp b/llvm/lib/CodeGen/TargetLoweringBase.cpp
index fe7bed7..16cd14b 100644
--- a/llvm/lib/CodeGen/TargetLoweringBase.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringBase.cpp
@@ -1738,15 +1738,8 @@ void llvm::GetReturnInfo(CallingConv::ID CC, Type *ReturnType,
     else if (attr.hasRetAttr(Attribute::ZExt))
       ExtendKind = ISD::ZERO_EXTEND;
 
-    // FIXME: C calling convention requires the return type to be promoted to
-    // at least 32-bit. But this is not necessary for non-C calling
-    // conventions. The frontend should mark functions whose return values
-    // require promoting with signext or zeroext attributes.
-    if (ExtendKind != ISD::ANY_EXTEND && VT.isInteger()) {
-      MVT MinVT = TLI.getRegisterType(MVT::i32);
-      if (VT.bitsLT(MinVT))
-        VT = MinVT;
-    }
+    if (ExtendKind != ISD::ANY_EXTEND && VT.isInteger())
+      VT = TLI.getTypeForExtReturn(ReturnType->getContext(), VT, ExtendKind);
 
     unsigned NumParts =
         TLI.getNumRegistersForCallingConv(ReturnType->getContext(), CC, VT);