On 06/19/2018 02:29 AM, Richard Biener wrote:
> On Mon, Jun 18, 2018 at 4:01 PM Wilco Dijkstra <wilco.dijks...@arm.com> wrote:
>>
>> GCC currently defaults to -fmath-errno. This generates code assuming math
>> functions set errno and the application checks errno. Few applications
>> test errno and various systems and math libraries no longer set errno since
>> it
>> is optional. GCC generates much faster code for simple math functions with
>> -fno-math-errno such as sqrt and lround (avoiding a call and PLT
>> redirection).
>> Therefore it is reasonable to change the default to -fno-math-errno. This is
>> already the case for non-C languages. Only change the default for C99 and
>> later.
>>
>> long f(float x) { return lroundf(x) + 1; }
>>
>> by default:
>>
>> f:
>> str x30, [sp, -16]!
>> bl lroundf
>> add x0, x0, 1
>> ldr x30, [sp], 16
>> ret
>>
>> With -fno-math-errno:
>>
>> f:
>> fcvtas x0, s0
>> add x0, x0, 1
>> ret
>>
>> Passes regress on AArch64. OK for commit?
>
> There are a number of regression tests that check for errno handling
> (I added some to avoid aliasing for example). Please make sure to
> add explicit -fmath-errno to those that do not already have it set
> (I guess such patch would be obvious and independent of this one).
>
> A grep -r errno testsuite/ is only 159 lines but it might not
> catch all cases - the one I'm refering to above matches because
> of a comment only:
>
> testsuite/gcc.dg/tree-ssa/ssa-dse-15.c: /* We should be able to DSE this
> store
> (p may point to errno). */
We're concerned about errno as potentially set by malloc here. It's
unrelated to the math-errno work.
Jeff
