[clang] [compiler-rt] [llvm] [SystemZ] Add support for half (fp16) (PR #109164)

[Jonas Paulsson via llvm-commits]

================
@@ -126,3 +138,23 @@ define void @f9(ptr %cptr, ptr %aptr, ptr %bptr) {
   store fp128 %c, ptr %cptr
   ret void
 }
+
+; Test f16 copies in which the sign comes from an f16.
+define half @f10(half %a, half %b) {
+; CHECK-LABEL: f10:
+; CHECK: brasl %r14, copysignh at PLT
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JonPsson1 wrote:

I have come to realize that these tests actually shouldn't involve copysignh at all, as here *libcalls* are tested.

On the other hand, if I compile a C program with copysign() using _Float16, Clang emits calls to the *intrinsic*:

```
 %0 = load half, ptr %v0, align 2, !tbaa !4
  %conv = fpext half %0 to double
  %1 = load half, ptr %v1, align 2, !tbaa !4
  %conv2 = fpext half %1 to double
  %2 = call double @llvm.copysign.f64(double %conv, double %conv2)
```
 
However the DAGCombiner will remove FPEXTs of the operands, so the backend still has to handle FCOPYSIGNs with one or two half operands (the ISD::FCOPYSIGN node can have the second argument of a different type). 

This is now implemented in lowerFCOPYSIGN() and tested in fp-copysign-03.ll.



https://github.com/llvm/llvm-project/pull/109164