[clang][RISCV] Set HasLegalHalfType to true if zfh is enabled

The desired semantics for HasLegalHalfType are slightly unclear in that
the comment for HasLegalHalfType says "True if the backend supports
operations on the half LLVM IR type." Which operations? We get very
limited scalar operations with zfhmin, more with zfh, and vector support
with zvfh. While the comment for hasLegalHalfType() says "Determine
whether _Float16 is supported on this target."

This patch sets HasLegalHalfType to true for zfh.

Differential Revision: https://reviews.llvm.org/D145071

Author: asb

clang/lib/Basic/Targets/RISCV.cpp

@@ -320,6 +320,9 @@ bool RISCVTargetInfo::handleTargetFeatures(std::vector<std::string> &Features,
   if (ABI.empty())
     ABI = ISAInfo->computeDefaultABI().str();
 
+  if (ISAInfo->hasExtension("zfh"))
+    HasLegalHalfType = true;
+
   return true;
 }
 

clang/test/CodeGen/RISCV/Float16-arith.c

@@ -11,8 +11,7 @@
 _Float16 x, y, z;
 
 // With no native half type support (no zfh), f16 will be promoted to f32.
-// With zfh, it shouldn't be (FIXME: set HasLegalHalfType = true in order to
-// get this behaviour for zfh).
+// With zfh, it shouldn't be.
 
 // NOZFH-LABEL: define dso_local void @f16_add
 // NOZFH-SAME: () #[[ATTR0:[0-9]+]] {
@@ -30,12 +29,9 @@ _Float16 x, y, z;
 // ZFH-SAME: () #[[ATTR0:[0-9]+]] {
 // ZFH-NEXT:  entry:
 // ZFH-NEXT:    [[TMP0:%.*]] = load half, ptr @y, align 2
-// ZFH-NEXT:    [[EXT:%.*]] = fpext half [[TMP0]] to float
 // ZFH-NEXT:    [[TMP1:%.*]] = load half, ptr @z, align 2
-// ZFH-NEXT:    [[EXT1:%.*]] = fpext half [[TMP1]] to float
-// ZFH-NEXT:    [[ADD:%.*]] = fadd float [[EXT]], [[EXT1]]
-// ZFH-NEXT:    [[UNPROMOTION:%.*]] = fptrunc float [[ADD]] to half
-// ZFH-NEXT:    store half [[UNPROMOTION]], ptr @x, align 2
+// ZFH-NEXT:    [[ADD:%.*]] = fadd half [[TMP0]], [[TMP1]]
+// ZFH-NEXT:    store half [[ADD]], ptr @x, align 2
 // ZFH-NEXT:    ret void
 //
 void f16_add() {