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Re: RFA: Fix tree-optimization/55524
- From: Joern Rennecke <joern dot rennecke at embecosm dot com>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Tue, 09 Apr 2013 12:24:33 -0400
- Subject: Re: RFA: Fix tree-optimization/55524
- References: <20130408111056 dot gvvtnyc8w04cww8g-nzlynne at webmail dot spamcop dot net> <CAFiYyc3Wea0cfqX8ARrRv0kpWvAS1P5MaH747Srqq=aU4E=jzQ at mail dot gmail dot com> <20130409105304 dot awkedy7bzwc8ww8o-nzlynne at webmail dot spamcop dot net> <CAFiYyc0fNDojG6suW8PJy4NLVR+PNQi1JZBwSfcWG3hHZHVc6w at mail dot gmail dot com>
Quoting Richard Biener <richard.guenther@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 .
gcc:
2013-04-09 Joern Rennecke <joern.rennecke@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.rennecke@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;