https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124039
Bug ID: 124039
Summary: [16 Regression] 401.bzip2 miscompares with -O3 on
Intel Ice Lake since r16-7324-g856ba1d7f786b0
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: pheeck at gcc dot gnu.org
CC: rguenth at gcc dot gnu.org
Blocks: 26163
Target Milestone: ---
Host: x86_64-pc-linux-gnu
Target: x86_64-pc-linux-gnu
Running the 401.bzip2 SPEC 2006 benchmark with -O3 -march=native on an Intel
Ice Lake (3rd generation Xeon) machine results in a miscompare:
****************************************
Contents of chicken.jpg.err
****************************************
(null): Data integrity error when decompressing.
****************************************
****************************************
Contents of input.combined.err
****************************************
(null): Data integrity error when decompressing.
****************************************
****************************************
Contents of input.source.err
****************************************
(null): Data integrity error when decompressing.
****************************************
****************************************
Contents of input.program.err
****************************************
(null): Data integrity error when decompressing.
****************************************
****************************************
Contents of text.html.err
****************************************
(null): Data integrity error when decompressing.
****************************************
*** Miscompare of chicken.jpg.out; for details see
/home/gcc/buildworker/source/cpu2006/benchspec/CPU2006/401.bzip2/run/run_peak_ref_amd64-m64-mine.0000/chicken.jpg.out.mis
'chicken.jpg.out' short
I bisected this to r16-7324-g856ba1d7f786b0
commit 856ba1d7f786b0b5e53042e292296391ae1b0da4
Author: Richard Biener <[email protected]>
Date: Thu Feb 5 11:09:59 2026 +0100
tree-optimization/123983 - only update IV on the requested edge
The following reverts back to only updating the IV after the
vectorized loop on the requested edge which avoids disrupting
live value vectorization.
PR tree-optimization/123983
* tree-vect-loop-manip.cc (vect_update_ivs_after_vectorizer):
Only update the PHI argument on the requested edge.
* gcc.dg/vect/vect-pr123983.c: New testcase.
gcc/testsuite/gcc.dg/vect/vect-pr123983.c | 28 ++++++++++++++++++++++++++++
gcc/tree-vect-loop-manip.cc | 16 ++--------------
2 files changed, 30 insertions(+), 14 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-pr123983.c
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26163
[Bug 26163] [meta-bug] missed optimization in SPEC (2k17, 2k and 2k6 and 95)
