https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120745
Bug ID: 120745
Summary: SEGV in process_uses_of_deleted_def, at
rtl-ssa/changes.cc:271
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: ondrejmachota at gmail dot com
CC: rsandifo at gcc dot gnu.org
Target Milestone: ---
Hi,
Jan Hubicka <hubi...@ucw.cz> and I are working on a new RTL DCE pass based on
the RTL SSA framework.
To help reproduce this bug, we have provided a branch:
refs/users/omachota/heads/rtl-ssa-dce (commit: eb73be9bde7). We tested our DCE
implementation agains UD_DCE, which deleted the same instructions in both
provided testcases.
Reduced testcase (921011-1.i):
int fun_th, fun_h;
void fun(int nb)
{
int sy;
while (nb)
while (fun_h)
if (++sy == fun_th)
sy = 0;
}
Run: gcc -c 921011-1.i -O1
Compiler output:
gcc: internal compiler error: Segmentation fault signal terminated program cc1
The bug occurs inside function process_uses_of_deleted_def. A phi_insn might
have a use pointing to itself.
When this use is processed by process_uses_of_deleted_def, the function
recurses (see rtl-ssa/changes.cc:271) until GCC crashes.
Compiler details:
Using built-in specs.
COLLECT_GCC=/mnt/tmpfs/gcc-install/usr/local/bin/gcc
COLLECT_LTO_WRAPPER=/mnt/tmpfs/gcc-install/usr/local/bin/../libexec/gcc/x86_64-pc-linux-gnu/15.0.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc/configure --enable-languages=c,c++ --disable-bootstrap
--disable-multilib --disable-libquadmath --disable-nls --disable-lto
--disable-shared --disable-threads
Thread model: single
Supported LTO compression algorithms: zlib zstd
gcc version 15.0.1 20250123 (experimental) (GCC)
Compiling GCC from the provided branch may fail. You might need to disable the
rtl_ssa_dce
pass, compile GCC, then re-enable the pass and compile again.
One more simplified testcase (testcase_pr82875.i):
char a;
long c, d;
void foo() {
while (0)
while (a)
lab:
d ? a %= c : 0;
goto lab;
}
Run: gcc -c testcase_pr82875.i -O1
Compiler output:
gcc: internal compiler error: Segmentation fault signal terminated program cc1
