Re: [PATCH] Don't optimize away throwing multiply in widening_mul pass (PR tree-optimization/51396)

[Richard Guenther <rguenther at suse dot de>]

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  <jakub@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 <rguenther@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
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