[Bug middle-end/102126] Wrong optimization of FP multiplication and division by 1 and -1 with -ftrapping-math when an underflow is possible

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102126

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Vincent Lefèvre from comment #2)
> In the testcase, I forgot
> 
> #pragma STDC FP_CONTRACT OFF
> 
> Anyway, it is currently ignored by GCC.

You can use -ffp-contract=off but I don't think these transforms are affected.

Note FENV_ACCESS is also ignored but then -ftrapping-math should indeed make
your testcase valid.  Are denormals standardized or left towards the
implementation?  One could argue the underflow exception with * 1 on a denormal
isn't covered?