On Mon, 5 Dec 2011, Jakub Jelinek wrote:
> Hi!
>
> When a multiply stmt has zero uses, convert_mult_to_fma immediately
> returns true, meaning the multiplication can be deleted. Normally it should
> be DCE job to remove dead stmts, not widening_mul pass IMHO, and in this
> case it shouldn't be removed because it can throw and wasn't DCEd because of
> it. For -fnon-call-exceptions if there is at least one use, we wouldn't be
> optimizing multiply and add/sub into FMA, because the multiplication
> (stmt_can_throw_p) would be in different bb from the addition/subtraction,
> so there is no need to purge dead eh edges etc. in the caller.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Ok.
Thanks,
Richard.
> 2011-12-05 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/51396
> * tree-ssa-math-opts.c (convert_mult_to_fma): Don't optimize
> if MUL_RESULT has zero uses.
>
> * g++.dg/opt/pr51396.C: New test.
>
> --- gcc/tree-ssa-math-opts.c.jj 2011-10-18 23:52:03.000000000 +0200
> +++ gcc/tree-ssa-math-opts.c 2011-12-05 19:00:42.467551532 +0100
> @@ -2429,6 +2429,12 @@ convert_mult_to_fma (gimple mul_stmt, tr
> if (optab_handler (fma_optab, TYPE_MODE (type)) == CODE_FOR_nothing)
> return false;
>
> + /* If the multiplication has zero uses, it is kept around probably because
> + of -fnon-call-exceptions. Don't optimize it away in that case,
> + it is DCE job. */
> + if (has_zero_uses (mul_result))
> + return false;
> +
> /* Make sure that the multiplication statement becomes dead after
> the transformation, thus that all uses are transformed to FMAs.
> This means we assume that an FMA operation has the same cost
> --- gcc/testsuite/g++.dg/opt/pr51396.C.jj 2011-12-05 19:03:36.793523559
> +0100
> +++ gcc/testsuite/g++.dg/opt/pr51396.C 2011-12-05 19:03:16.000000000
> +0100
> @@ -0,0 +1,24 @@
> +// PR tree-optimization/51396
> +// { dg-do compile }
> +// { dg-options "-O2 -fnon-call-exceptions -mfma" }
> +// { dg-options "-O2 -fnon-call-exceptions -mfma" { target i?86-*-*
> x86_64-*-* } }
> +
> +double baz (double) throw ();
> +
> +struct C
> +{
> + C (double d = 0.0) : c (d) {}
> + double c;
> +};
> +
> +static inline void
> +foo (double x, const C &y)
> +{
> + x ? (y.c * baz (x)) : (C (), y);
> +}
> +
> +void
> +bar (double x, C y)
> +{
> + foo (x, y);
> +}
>
> Jakub
>
>
--
Richard Guenther <rguent...@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer
