[libclc] [libclc] Reduce bithacking for INF/NAN values (PR #129738)

[Matt Arsenault via cfe-commits]

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@@ -46,9 +46,7 @@ _CLC_DEF _CLC_OVERLOAD __CLC_GENTYPE __clc_hypot(__CLC_GENTYPE x,
   __CLC_GENTYPE retval = __clc_sqrt(__clc_mad(fx, fx, fy * fy)) * fx_exp;
 
   retval = (ux > PINFBITPATT_SP32 || uy == 0) ? __CLC_AS_GENTYPE(ux) : retval;
-  retval = (ux == PINFBITPATT_SP32 || uy == PINFBITPATT_SP32)
-               ? __CLC_AS_GENTYPE((__CLC_UINTN)PINFBITPATT_SP32)
-               : retval;
+  retval = __clc_isinf(x) || __clc_isinf(y) ? __CLC_GENTYPE_INF : retval;
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arsenm wrote:

> But if the AMDGPU version of "frexp_mant" does subnormal scaling and other targets don't, then that could cause bugs between platforms as now we can't guarantee the bits that come out of the frexp_mant and frexp_exp helpers.

If they don't handle denormals, it's an incorrect implementation of frexp or frexp_mant. The operation is not simply mask out the exponent bits. The clamping to 126 code above is dealing with the denormal cases. That can be folded into a software frexp_mant utility which happens to be one instruction for amdgpu 

https://github.com/llvm/llvm-project/pull/129738