On Tue, Apr 9, 2013 at 6:24 PM, Joern Rennecke
<joern.renne...@embecosm.com> wrote:
> Quoting Richard Biener <richard.guent...@gmail.com>:
>
>> I don't see that. It's merely a complication of optimal handling of
>> a * b +- c * d vs. just a * b +- c. The pass does simple pattern matching
>> only, not doing a global optimal transform, so adding another special-case
>> is reasonable. Special-casing just for single-use 2nd multiplication
>> simplifies the cases for example.
>
>
> I have attached a version of the patch that uses this simpler test.
> Currently bootstrapping / regtesting on i686-pc-linux-gnu .
Ok if the testing succeeds.
Thanks,
Richard.
>
> gcc:
> 2013-04-09 Joern Rennecke <joern.renne...@embecosm.com>
>
> PR tree-optimization/55524
> * tree-ssa-math-opts.c
> (convert_mult_to_fma): Don't use an fms construct
> when we don't have an fms operation, but fnma, and it looks
> likely that we'll be able to use the latter.
>
> gcc/testsuite:
> 2013-04-09 Joern Rennecke <joern.renne...@embecosm.com>
>
> PR tree-optimization/55524
> * gcc.target/epiphany/fnma-1.c: New test.
>
> Index: testsuite/gcc.target/epiphany/fnma-1.c
> ===================================================================
> --- testsuite/gcc.target/epiphany/fnma-1.c (revision 0)
> +++ testsuite/gcc.target/epiphany/fnma-1.c (working copy)
> @@ -0,0 +1,9 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +/* { dg-final { scan-assembler-times "fmsub\[ \ta-zA-Z0-9\]*," 1 } } */
> +
> +float
> +f (float ar, float ai, float br, float bi)
> +{
> + return ar * br - ai * bi;
> +}
> Index: tree-ssa-math-opts.c
> ===================================================================
> --- tree-ssa-math-opts.c (revision 197578)
> +++ tree-ssa-math-opts.c (working copy)
> @@ -2570,6 +2570,24 @@ convert_mult_to_fma (gimple mul_stmt, tr
> return false;
> }
>
> + /* If the subtrahend (gimple_assign_rhs2 (use_stmt)) is computed
> + by a MULT_EXPR that we'll visit later, we might be able to
> + get a more profitable match with fnma.
> + OTOH, if we don't, a negate / fma pair has likely lower latency
> + that a mult / subtract pair. */
> + if (use_code == MINUS_EXPR && !negate_p
> + && gimple_assign_rhs1 (use_stmt) == result
> + && optab_handler (fms_optab, TYPE_MODE (type)) == CODE_FOR_nothing
> + && optab_handler (fnma_optab, TYPE_MODE (type)) !=
> CODE_FOR_nothing)
> + {
> + tree rhs2 = gimple_assign_rhs2 (use_stmt);
> + gimple stmt2 = SSA_NAME_DEF_STMT (rhs2);
> +
> + if (has_single_use (rhs2)
> + && gimple_assign_rhs_code (stmt2) == MULT_EXPR)
> + return false;
> + }
> +
> /* We can't handle a * b + a * b. */
> if (gimple_assign_rhs1 (use_stmt) == gimple_assign_rhs2 (use_stmt))
> return false;
>
