On 2026-03-03 13:19, Richard Biener wrote:
On Tue, 3 Mar 2026, Torbjorn SVENSSON wrote:
Hi Richard,
This patch causes a regression for arm-none-eabi (log snippet is from a more
recent build of GCC):
Testing complex/fast-math-complex-add-pattern-half-float.c
doing compile
Executing on host: /build/r16-7849-g1f9879e17466f5/bin/arm-none-eabi-gcc
/build/gcc_src/gcc/testsuite/gcc.dg/vect/complex/fast-math-complex-add-pattern-half-float.c
-mthumb -march=armv6s-m -mtune=cortex-m0 -mfloat-abi=soft -mfpu=auto
-fdiagnostics-plain-output -mfloat-abi=softfp -mcpu=unset
-march=armv7-a+simd -mfpu=auto -ffast-math -ftree-vectorize
-fno-tree-loop-distribute-patterns -fno-vect-cost-model -fno-common -O2
-fdump-tree-vect-details -ffast-math -mfloat-abi=softfp -mfpu=auto -mcpu=unset
-march=armv8.3-a+fp16+simd -S -o
fast-math-complex-add-pattern-half-float.s (timeout = 800)
spawn -ignore SIGHUP /build/r16-7849-g1f9879e17466f5/bin/arm-none-eabi-gcc
/build/gcc_src/gcc/testsuite/gcc.dg/vect/complex/fast-math-complex-add-pattern-half-float.c
-mthumb -march=armv6s-m -mtune=cortex-m0 -mfloat-abi=soft -mfpu=auto
-fdiagnostics-plain-output -mfloat-abi=softfp -mcpu=unset -march=armv7-a+simd
-mfpu=auto -ffast-math -ftree-vectorize -fno-tree-loop-distribute-patterns
-fno-vect-cost-model -fno-common -O2 -fdump-tree-vect-details -ffast-math
-mfloat-abi=softfp -mfpu=auto -mcpu=unset -march=armv8.3-a+fp16+simd -S -o
fast-math-complex-add-pattern-half-float.s
pid is 2955587 -2955587
pid is -1
output is status 0
PASS: gcc.dg/vect/complex/fast-math-complex-add-pattern-half-float.c (test for
excess errors)
gcc.dg/vect/complex/fast-math-complex-add-pattern-half-float.c: pattern found
4 times
FAIL: gcc.dg/vect/complex/fast-math-complex-add-pattern-half-float.c
scan-tree-dump-times vect "add new stmt: [^\n\r]*COMPLEX_ADD_ROT90" 3
PASS: gcc.dg/vect/complex/fast-math-complex-add-pattern-half-float.c
PASS: scan-tree-dump-times vect "add new stmt: [^\n\r]*COMPLEX_ADD_ROT270" 1
PASS: gcc.dg/vect/complex/fast-math-complex-add-pattern-half-float.c
PASS: scan-tree-dump vect "Found COMPLEX_ADD_ROT270"
PASS: gcc.dg/vect/complex/fast-math-complex-add-pattern-half-float.c
PASS: scan-tree-dump vect "Found COMPLEX_ADD_ROT90"
Should the test be updated to accept 4 pattern matches or is it wrong to have
4 matches instead of 3?
We see epilogue vectorization here. The best way forward is probably
to add --param vect-epilogues-nomask=0 to dg-additional-options in that
testcase. I verified this fixes the issue on aarch64 with
-march=armv8.3-a.
Can you test arm-none-eabi? arm and aarch64 are the only targets
enabled by vect_complex_add_half.
Adding "--param vect-epilogues-nomask=0" to dg-additional-options works fine
for the targets that I test on arm-none-eabi.
Do you want me to send a patch with this or will you handle it?
Kind regards,
Torbjörn
Richard.
Kind regards,
Torbjörn
On 2026-01-14 12:52, Richard Biener wrote:
The following adjusts the condition where we reject vectorization
because the scalar loop runs only for a single iteration (or two,
in case we need to peel for gaps). Because this is over-eager
when considering the case of VF == 1 where instead the cost model
should decide wheter it is worthwhile or not. I'm playing
conservative here and exclude the case of two iterations as I
do not have benchmark evidence.
This helps fixing a regression observed with improved SLP handling,
not exactly for the options used in the PR though, but for a more
common -O3 -march=x86-64-v3 this speeds up 433.milc by 6%.
Bootstrapped and tested on x86_64-unknown-linux-gnu, will push later.
PR tree-optimization/123190
* tree-vect-loop.cc (vect_analyze_loop_costing): Allow
vectorizing loops with a single scalar iteration iff the
vectorization factor is 1.
* gcc.dg/vect/costmodel/x86_64/costmodel-pr123190-1.c: New testcase.
* gcc.dg/vect/slp-28.c: Avoid epilogue vectorization for
simplicity.
---
.../costmodel/x86_64/costmodel-pr123190-1.c | 38 +++++++++++++++++++
gcc/testsuite/gcc.dg/vect/slp-28.c | 1 +
gcc/tree-vect-loop.cc | 8 +++-
3 files changed, 45 insertions(+), 2 deletions(-)
create mode 100644
gcc/testsuite/gcc.dg/vect/costmodel/x86_64/costmodel-pr123190-1.c
diff --git
a/gcc/testsuite/gcc.dg/vect/costmodel/x86_64/costmodel-pr123190-1.c
b/gcc/testsuite/gcc.dg/vect/costmodel/x86_64/costmodel-pr123190-1.c
new file mode 100644
index 00000000000..4265ac80a43
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/costmodel/x86_64/costmodel-pr123190-1.c
@@ -0,0 +1,38 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-O3 -mavx2 -mno-avx512f -mtune=generic" } */
+
+typedef struct {
+ double real;
+ double imag;
+} complex;
+
+typedef struct { complex e[3][3]; } su3_matrix;
+
+void mult_su3_na( su3_matrix *a, su3_matrix *b, su3_matrix *c ){
+int i,j;
+register double t,ar,ai,br,bi,cr,ci;
+ for(i=0;i<3;i++)
+ for(j=0;j<3;j++){
+
+ ar=a->e[i][0].real; ai=a->e[i][0].imag;
+ br=b->e[j][0].real; bi=b->e[j][0].imag;
+ cr=ar*br; t=ai*bi; cr += t;
+ ci=ai*br; t=ar*bi; ci -= t;
+
+ ar=a->e[i][1].real; ai=a->e[i][1].imag;
+ br=b->e[j][1].real; bi=b->e[j][1].imag;
+ t=ar*br; cr += t; t=ai*bi; cr += t;
+ t=ar*bi; ci -= t; t=ai*br; ci += t;
+
+ ar=a->e[i][2].real; ai=a->e[i][2].imag;
+ br=b->e[j][2].real; bi=b->e[j][2].imag;
+ t=ar*br; cr += t; t=ai*bi; cr += t;
+ t=ar*bi; ci -= t; t=ai*br; ci += t;
+
+ c->e[i][j].real=cr;
+ c->e[i][j].imag=ci;
+ }
+}
+
+/* { dg-final { scan-tree-dump "optimized: loop vectorized using 32" "vect"
} } */
+/* { dg-final { scan-tree-dump "optimized: epilogue loop vectorized using
16 byte vectors and unroll factor 1" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/slp-28.c
b/gcc/testsuite/gcc.dg/vect/slp-28.c
index 1f987874f0d..bf6271eed25 100644
--- a/gcc/testsuite/gcc.dg/vect/slp-28.c
+++ b/gcc/testsuite/gcc.dg/vect/slp-28.c
@@ -1,4 +1,5 @@
/* { dg-require-effective-target vect_int } */
+/* { dg-additional-options "--param vect-epilogues-nomask=0" } */
#include <stdarg.h>
#include "tree-vect.h"
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 74eecb832e6..fdf544fa47b 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -1792,9 +1792,13 @@ vect_analyze_loop_costing (loop_vec_info loop_vinfo,
}
}
/* Reject vectorizing for a single scalar iteration, even if
- we could in principle implement that using partial vectors. */
+ we could in principle implement that using partial vectors.
+ But allow such vectorization if VF == 1 in case we do not
+ need to peel for gaps (if we need, avoid vectorization for
+ reasons of code footprint). */
unsigned peeling_gap = LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo);
- if (scalar_niters <= peeling_gap + 1)
+ if (scalar_niters <= peeling_gap + 1
+ && (assumed_vf > 1 || peeling_gap != 0))
{
if (dump_enabled_p ())
dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
