https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109072
Bug ID: 109072
Summary: [12/13 Regression] SLP costs for vec duplicate too
high since g:4963079769c99c4073adfd799885410ad484cbbe
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: tnfchris at gcc dot gnu.org
CC: rsandifo at gcc dot gnu.org
Target Milestone: ---
Target: aarch64*
The following example
---
#include <arm_neon.h>
float32x4_t f (float32x4_t v, float res)
{
float data[4];
data[0] = res;
data[1] = res;
data[2] = res;
data[3] = res;
return vld1q_f32 (&data[0]);
}
---
compiled with -Ofast fails to SLP starting with GCC 12.
This used to generate:
f:
dup v0.4s, v1.s[0]
ret
and now generates:
f:
fmov w5, s1
fmov w1, s1
fmov w4, s1
fmov w0, s1
mov x2, 0
mov x3, 0
bfi x2, x5, 0, 32
bfi x3, x1, 0, 32
bfi x2, x4, 32, 32
bfi x3, x0, 32, 32
fmov d0, x2
ins v0.d[1], x3
ret
The SLP costs went from:
Vector cost: 2
Scalar cost: 4
to:
Vector cost: 12
Scalar cost: 4
it looks like it's no longer costing it as a duplicate but instead 4 vec
inserts.
bisected to:
commit g:4963079769c99c4073adfd799885410ad484cbbe
Author: Richard Sandiford <richard.sandif...@arm.com>
Date: Tue Feb 15 18:09:33 2022 +0000
vect+aarch64: Fix ldp_stp_* regressions
ldp_stp_1.c, ldp_stp_4.c and ldp_stp_5.c have been failing since
vectorisation was enabled at -O2. In all three cases SLP is
generating vector code when scalar code would be better.
....
