RE: [PATCH v4] [tree-optimization/110279] Consider FMA in get_reassociation_width

[Di Zhao OS <dizhao@os.amperecomputing.com>]

Hello Thomas,

> -----Original Message-----
> From: Thomas Schwinge <thomas@codesourcery.com>
> Sent: Friday, December 15, 2023 5:46 PM
> To: Di Zhao OS <dizhao@os.amperecomputing.com>; gcc-patches@gcc.gnu.org
> Cc: Richard Biener <richard.guenther@gmail.com>
> Subject: RE: [PATCH v4] [tree-optimization/110279] Consider FMA in
> get_reassociation_width
> 
> Hi!
> 
> On 2023-12-13T08:14:28+0000, Di Zhao OS <dizhao@os.amperecomputing.com> wrote:
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/pr110279-2.c
> > @@ -0,0 +1,41 @@
> > +/* PR tree-optimization/110279 */
> > +/* { dg-do compile } */
> > +/* { dg-options "-Ofast --param tree-reassoc-width=4 --param fully-
> pipelined-fma=1 -fdump-tree-reassoc2-details -fdump-tree-optimized" } */
> > +/* { dg-additional-options "-march=armv8.2-a" { target aarch64-*-* } } */
> > +
> > +#define LOOP_COUNT 800000000
> > +typedef double data_e;
> > +
> > +#include <stdio.h>
> > +
> > +__attribute_noinline__ data_e
> > +foo (data_e in)
> 
> Pushed to master branch commit 91e9e8faea4086b3b8aef2355fc12c1559d425f6
> "Fix 'gcc.dg/pr110279-2.c' syntax error due to '__attribute_noinline__'",
> see attached.
> 
> However:
> 
> > +{
> > +  data_e a1, a2, a3, a4;
> > +  data_e tmp, result = 0;
> > +  a1 = in + 0.1;
> > +  a2 = in * 0.1;
> > +  a3 = in + 0.01;
> > +  a4 = in * 0.59;
> > +
> > +  data_e result2 = 0;
> > +
> > +  for (int ic = 0; ic < LOOP_COUNT; ic++)
> > +    {
> > +      /* Test that a complete FMA chain with length=4 is not broken.  */
> > +      tmp = a1 + a2 * a2 + a3 * a3 + a4 * a4 ;
> > +      result += tmp - ic;
> > +      result2 = result2 / 2 - tmp;
> > +
> > +      a1 += 0.91;
> > +      a2 += 0.1;
> > +      a3 -= 0.01;
> > +      a4 -= 0.89;
> > +
> > +    }
> > +
> > +  return result + result2;
> > +}
> > +
> > +/* { dg-final { scan-tree-dump-not "was chosen for reassociation"
> "reassoc2"} } */
> > +/* { dg-final { scan-tree-dump-times {\.FMA } 3 "optimized"} } */

Thank you for the fix.

> ..., I still see these latter two tree dump scans FAIL, for GCN:
> 
>     $ grep -C2 'was chosen for reassociation' pr110279-2.c.197t.reassoc2
>       2 *: a3_40
>       2 *: a2_39
>     Width = 4 was chosen for reassociation
>     Transforming _15 = powmult_1 + powmult_3;
>      into _63 = powmult_1 + a1_38;
>     $ grep -F .FMA pr110279-2.c.265t.optimized
>       _63 = .FMA (a2_39, a2_39, a1_38);
>       _64 = .FMA (a3_40, a3_40, powmult_5);
> 
> ..., nvptx:
> 
>     $ grep -C2 'was chosen for reassociation' pr110279-2.c.197t.reassoc2
>       2 *: a3_40
>       2 *: a2_39
>     Width = 4 was chosen for reassociation
>     Transforming _15 = powmult_1 + powmult_3;
>      into _63 = powmult_1 + a1_38;
>     $ grep -F .FMA pr110279-2.c.265t.optimized
>       _63 = .FMA (a2_39, a2_39, a1_38);
>       _64 = .FMA (a3_40, a3_40, powmult_5);

For these 2 targets, the reassoc_width for FMUL is 1 (default value),
While the testcase assumes that to be 4. The bug was introduced when I
updated the patch but forgot to update the testcase.

> ..., but also x86_64-pc-linux-gnu:
> 
>     $  grep -C2 'was chosen for reassociation' pr110279-2.c.197t.reassoc2
>       2 *: a3_40
>       2 *: a2_39
>     Width = 2 was chosen for reassociation
>     Transforming _15 = powmult_1 + powmult_3;
>      into _63 = powmult_1 + powmult_3;
>     $ grep -cF .FMA pr110279-2.c.265t.optimized
>     0

For x86_64 this needs "-mfma". Sorry the compile options missed that.
Can the change below fix these issues? I moved them into
testsuite/gcc.target/aarch64, since they rely on tunings.

Tested on aarch64-unknown-linux-gnu.

> 
> Grüße
>  Thomas
> 
> 
> -----------------
> Siemens Electronic Design Automation GmbH; Anschrift: Arnulfstraße 201, 80634
> München; Gesellschaft mit beschränkter Haftung; Geschäftsführer: Thomas
> Heurung, Frank Thürauf; Sitz der Gesellschaft: München; Registergericht
> München, HRB 106955

Thanks,
Di Zhao

---
 gcc/testsuite/{gcc.dg => gcc.target/aarch64}/pr110279-1.c | 3 +--
 gcc/testsuite/{gcc.dg => gcc.target/aarch64}/pr110279-2.c | 3 +--
 2 files changed, 2 insertions(+), 4 deletions(-)
 rename gcc/testsuite/{gcc.dg => gcc.target/aarch64}/pr110279-1.c (83%)
 rename gcc/testsuite/{gcc.dg => gcc.target/aarch64}/pr110279-2.c (78%)

diff --git a/gcc/testsuite/gcc.dg/pr110279-1.c b/gcc/testsuite/gcc.target/aarch64/pr110279-1.c
similarity index 83%
rename from gcc/testsuite/gcc.dg/pr110279-1.c
rename to gcc/testsuite/gcc.target/aarch64/pr110279-1.c
index f25b6aec967..97d693f56a5 100644
--- a/gcc/testsuite/gcc.dg/pr110279-1.c
+++ b/gcc/testsuite/gcc.target/aarch64/pr110279-1.c
@@ -1,6 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-Ofast --param avoid-fma-max-bits=512 --param tree-reassoc-width=4 -fdump-tree-widening_mul-details" } */
-/* { dg-additional-options "-march=armv8.2-a" { target aarch64-*-* } } */
+/* { dg-options "-Ofast -mcpu=generic --param avoid-fma-max-bits=512 --param tree-reassoc-width=4 -fdump-tree-widening_mul-details" } */
 
 #define LOOP_COUNT 800000000
 typedef double data_e;
diff --git a/gcc/testsuite/gcc.dg/pr110279-2.c b/gcc/testsuite/gcc.target/aarch64/pr110279-2.c
similarity index 78%
rename from gcc/testsuite/gcc.dg/pr110279-2.c
rename to gcc/testsuite/gcc.target/aarch64/pr110279-2.c
index b6b69969c6b..a88cb361fdc 100644
--- a/gcc/testsuite/gcc.dg/pr110279-2.c
+++ b/gcc/testsuite/gcc.target/aarch64/pr110279-2.c
@@ -1,7 +1,6 @@
 /* PR tree-optimization/110279 */
 /* { dg-do compile } */
-/* { dg-options "-Ofast --param tree-reassoc-width=4 --param fully-pipelined-fma=1 -fdump-tree-reassoc2-details -fdump-tree-optimized" } */
-/* { dg-additional-options "-march=armv8.2-a" { target aarch64-*-* } } */
+/* { dg-options "-Ofast -mcpu=generic --param tree-reassoc-width=4 --param fully-pipelined-fma=1 -fdump-tree-reassoc2-details -fdump-tree-optimized" } */
 
 #define LOOP_COUNT 800000000
 typedef double data_e;
-- 
2.25.1