On October 27, 2021 4:44:53 PM GMT+02:00, Jakub Jelinek <ja...@redhat.com>
wrote:
>On Wed, Oct 27, 2021 at 04:29:38PM +0200, Richard Biener wrote:
>> So something like the following below? Note I have to fix
>> simplify_const_unary_operation to not perform the invalid constant
>> folding with (not worrying about the exact conversion case - I doubt
>> any of the constant folding is really relevant on RTL these days,
>> maybe we should simply punt for all unary float-float ops when either
>> mode has sign dependent rounding modes)
>>
>> diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
>> index bbbd6b74942..9522a31570e 100644
>> --- a/gcc/simplify-rtx.c
>> +++ b/gcc/simplify-rtx.c
>> @@ -2068,6 +2073,9 @@ simplify_const_unary_operation (enum rtx_code code,
>> machine_mode mode,
>> and the operand is a signaling NaN. */
>> if (HONOR_SNANS (mode) && REAL_VALUE_ISSIGNALING_NAN (d))
>> return NULL_RTX;
>> + /* Or if flag_rounding_math is on. */
>> + if (HONOR_SIGN_DEPENDENT_ROUNDING (mode))
>> + return NULL_RTX;
>> d = real_value_truncate (mode, d);
>> break;
>
>Won't this stop folding of truncations that are never a problem?
>I mean at least if the wider float mode constant is exactly representable
>in the narrower float mode, no matter what rounding mode is used the value
>will be always the same...
>And people use
> float f = 1.0;
>or
> float f = 1.25;
>etc. a lot.
Yes, but I do expect any such opportunities to be realized on GENERIC/GIMPLE?
>So perhaps again
> if (HONOR_SIGN_DEPENDENT_ROUNDING (mode)
> && !exact_real_truncate (mode, &d))
> return NULL_RTX;
>?
Sure, for this case it's short and straight forward.
>
>> /* PR57245 */
>> /* { dg-do run } */
>> /* { dg-require-effective-target fenv } */
>> /* { dg-additional-options "-frounding-math" } */
>>
>> #include <fenv.h>
>> #include <stdlib.h>
>>
>> int
>> main ()
>> {
>
>Roughly yes. Some tests also do #ifdef FE_*, so in your case
>> #if __DBL_MANT_DIG__ == 53 && __FLT_MANT_DIG__ == 24
>+#ifdef FE_UPWARD
Ah, OK. Will fix.
Richard.
>> fesetround (FE_UPWARD);
>> float f = 1.3;
>> if (f != 0x1.4ccccep+0f)
>> __builtin_abort ();
>+#endif
>+#ifdef FE_TONEAREST
>etc.
>> fesetround (FE_TONEAREST);
>> /* Use different actual values so the bogus CSE we perform does not
>> break things. */
>> f = 1.33;
>> if (f != 0x1.547ae2p+0f)
>> abort ();
>> fesetround (FE_DOWNWARD);
>> f = 1.333;
>> if (f != 0x1.553f7cp+0f)
>> abort ();
>> fesetround (FE_TOWARDZERO);
>> f = 1.3333;
>> if (f != 0x1.555326p+0f)
>> abort ();
>> #endif
>> return 0;
>> }
>
> Jakub
>
