[PATCH] D71467: [FPEnv] Generate constrained FP comparisons from clang

[Ulrich Weigand via Phabricator via llvm-commits]

uweigand added a comment.

In D71467#1786192 <https://reviews.llvm.org/D71467#1786192>, @erichkeane wrote:

> __builtin_fpclassify/isfinite/isinf/isinf_sign/isnan/isnormal/signbit are all implemented the same as the OTHER ones, except there is a strange fixup step in SEMA that removes the float->double cast.  It is IMO the wrong way to do it.
>
> I don't think it would modify the IR at all or the AST, but I'm also working on removing that hack (which is what I meant by the fp-classification type ones).
>
> I hope the work I've done already is sufficient to unblock this patch.


Yes, this patch is no longer blocked, thanks!

What I was trying to say is that there is a fundamental difference between the comparison builtins like isless, isgreater, etc. and the classification builtins like isinf, isnan, etc.

The former **should** result in comparison instructions being generated, the only difference between the builtin and a regular "<" operator is that the builtin emits a quiet compare while the operator emits a signaling compare in strict mode.

However, the latter (classification macros) should not actually emit **any** comparison instructions in strict mode, because the classification macros may never trap, but all comparison instructions do.  So the basic idea of implementing e.g. isinf(x) as "fabs(x) == infinity"  (like the comment in CGBuiltin.cpp currently says) is fundamentally wrong in strict mode.


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