[PATCH] D113107: Support of expression granularity for _Float16.

John McCall via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Wed Jun 22 12:44:45 PDT 2022

rjmccall added a comment.

In D113107#3602478 <https://reviews.llvm.org/D113107#3602478>, @zahiraam wrote:

> Do we want to add an -fexcess-precision option?

Well, generally we try to offer the same options GCC does.  However, it looks like GCC's `-fexcess-precision` does not line up with the options we're thinking of offering: GCC offers only `-fexcess-precision=standard` (essentially what you're implementing) and `-fexcess-precision=fast` (which I think would require some sort of optimizer annotation to permit folding truncations across statement boundaries), with no option to get operation-by-operation fidelity (our current behavior).  And I think we're very unlikely to default to `-fexcess-precision=fast` the way that GCC apparently does.  I'm also not sure if anyone cares enough to enable this for anything other than `_Float16`; on GCC, `-fexcess-precision` is much broader, e.g. affecting `float` and `double` math on non-SSE x86 targets.  So I think we should hold off on adding this option until we know what behavior we actually want to expose via it.



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