https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123014
Bug ID: 123014
Summary: [16 Regression] Recent change causes SSA graph
inconsistency
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: law at gcc dot gnu.org
Target Milestone: ---
This change:
commit 4a1247a3b070cdb02910826a5effb505457a6e73
Author: Tamar Christina <[email protected]>
Date: Wed Dec 3 10:55:40 2025 +0000
vect: delay identification of update_e until after skip_epilog [PR122959]
The testcase attached in the PR shows that for some reason
the test openmp_vv.sum when doing OpenMP offloading creates
an intermediate empty block after the skip_epilog split.
This means we should just simply delay setting update_e for
the non-early break case. For early break we have to do it
early still otherwise the skip_epilog edge would make us find
the wrong edge.
I haven't been able to replicate this on a C testcase and the
attached reduction works fine on AArch64 and x86_64 but have
been able to verify the fixed code with
./gcc/f951 -fopenmp test2.f90 -O3 -o - -march=sm_30 on an
--target=nvptx-none --enable-as-accelerator-for=x86_64-pc-linux-gnu
configured cc1.
If I manage to create a testcase will push it too.
gcc/ChangeLog:
PR middle-end/122959
* tree-vect-loop-manip.cc (vect_do_peeling): Delay setting
update_e.
Causes an ICE for gcc.dg/pr95854.c on arc-elf. Given it's an ICE you shouldn't
need a full cross environment to trigger.
root@276ff1154e08:/home/jlaw/jenkins/workspace/arc-elf/arc-elf-obj/gcc/gcc#
./cc1 -O3 pr95854.c -fno-vect-cost-model -fno-tree-scev-cprop -quiet
pr95854.c: In function 'main':
pr95854.c:7:5: error: definition in block 18 does not dominate use in block 15
7 | int main()
| ^~~~
for SSA_NAME: tmp.25_17 in statement:
_49 = PHI <_36(16), tmp.25_17(15)>
PHI argument
tmp.25_17
for PHI node
_49 = PHI <_36(16), tmp.25_17(15)>
during GIMPLE pass: vect
pr95854.c:7:5: internal compiler error: verify_ssa failed
0x26770dd internal_error(char const*, ...)
../../..//gcc/gcc/diagnostic-global-context.cc:787
0x17a2340 verify_ssa(bool, bool)
../../..//gcc/gcc/tree-ssa.cc:1203
