[libclc] [libclc] Move sign to the CLC builtins library (PR #115699)

[Matt Arsenault via cfe-commits]

================
@@ -0,0 +1,21 @@
+// TYPE sign(TYPE x) {
+//   if (isnan(x)) {
+//     return 0.0F;
+//   }
+//   if (x > 0.0F) {
+//     return 1.0F;
+//   }
+//   if (x < 0.0F) {
+//     return -1.0F;
+//   }
+//   return x; /* -0.0 or +0.0 */
+// }
+_CLC_DEF _CLC_OVERLOAD __CLC_GENTYPE __clc_sign(__CLC_GENTYPE x) {
+  __CLC_BIT_INTN x_isnan = __clc_isnan(x);
+  __CLC_BIT_INTN x_isgreater_zero = x > __CLC_FP_LIT(0.0);
+  __CLC_BIT_INTN x_isless_zero = x < __CLC_FP_LIT(0.0);
+  __CLC_GENTYPE sel0 = __clc_select(x, __CLC_FP_LIT(1.0), x_isgreater_zero);
+  __CLC_GENTYPE sel1 = __clc_select(sel0, __CLC_FP_LIT(-1.0), x_isless_zero);
+  __CLC_GENTYPE sel2 = __clc_select(sel1, __CLC_FP_LIT(0.0), x_isnan);
+  return sel2;
+}
----------------
arsenm wrote:


How about this:
```
int sign(float x) {
    return copysign((__builtin_isnan(x) | (x == 0.0f)) ? 0.0f : 1.0f, x);
}
```

produces:
```
define hidden i32 @test_sign(float noundef %x) #0 {
entry:
  %or4 = fcmp ueq float %x, 0.000000e+00
  %cond = select i1 %or4, float 0.000000e+00, float 1.000000e+00
  %call = tail call float @llvm.copysign.f32(float noundef %cond, float noundef 
%x) #2
  %conv1 = fptosi float %call to i32
  ret i32 %conv1
}
```


https://github.com/llvm/llvm-project/pull/115699
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