https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109002
Bug ID: 109002
Summary: -O1 -ftree-pre -ftree-partial-pre results in stall
value
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: akihiko.odaki at daynix dot com
Target Milestone: ---
The following should emit an executable which prints "a" forever, but the
actual compiled executable prints nothing and just hangs. It seems the code
sees a stall value of variable g.
gcc -O1 -ftree-pre -ftree-partial-pre -x c - <<EOF
#include <stdio.h>
int g;
int h;
int main(void)
{
for (int i = 0; ; i++) {
for (int j = 0; j < g; j++);
if (i & 1) {
if (h)
continue;
if (g)
puts("a");
g = 1;
}
}
}
EOF
I reproduced this bug with the current master. gcc -v says:
Using built-in specs.
COLLECT_GCC=/home/alarm/gcc-installation/usr/local/bin/gcc
COLLECT_LTO_WRAPPER=/home/alarm/gcc-installation/usr/local/bin/../libexec/gcc/aarch64-unknown-linux-gnu/13.0.1/lto-wrapper
Target: aarch64-unknown-linux-gnu
Configured with: ../gcc/configure --disable-bootstrap : (reconfigured)
../gcc/configure --disable-bootstrap
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.0.1 20230302 (experimental) (GCC)
COLLECT_GCC_OPTIONS='-v' '-mlittle-endian' '-mabi=lp64'
/home/alarm/gcc-installation/usr/local/bin/../libexec/gcc/aarch64-unknown-linux-gnu/13.0.1/cc1
-quiet -v -iprefix
/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/
/home/alarm/a.c -quiet -dumpbase a.c -dumpbase-ext .c -mlittle-endian
-mabi=lp64 -version -o /tmp/ccetU9yt.s
GNU C17 (GCC) version 13.0.1 20230302 (experimental)
(aarch64-unknown-linux-gnu)
compiled by GNU C version 12.1.0, GMP version 6.2.1, MPFR version
4.2.0, MPC version 1.3.1, isl version isl-0.25-GMP
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
ignoring nonexistent directory
"/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/../../../../aarch64-unknown-linux-gnu/include"
ignoring duplicate directory
"/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/../../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/include"
ignoring duplicate directory
"/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/../../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/include-fixed"
ignoring nonexistent directory
"/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/../../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/../../../../aarch64-unknown-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/include
/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/include-fixed
/usr/local/include
/usr/include
End of search list.
Compiler executable checksum: 374b2759695ed1b72f52cb0f1847fbb3
COLLECT_GCC_OPTIONS='-v' '-mlittle-endian' '-mabi=lp64'
as -v -EL -mabi=lp64 -o /tmp/ccTu98hj.o /tmp/ccetU9yt.s
GNU assembler version 2.38 (aarch64-unknown-linux-gnu) using BFD version (GNU
Binutils) 2.38
COMPILER_PATH=/home/alarm/gcc-installation/usr/local/bin/../libexec/gcc/aarch64-unknown-linux-gnu/13.0.1/:/home/alarm/gcc-installation/usr/local/bin/../libexec/gcc/
LIBRARY_PATH=/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/:/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/:/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/../../../../lib64/:/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-mlittle-endian' '-mabi=lp64' '-dumpdir' 'a.'
/home/alarm/gcc-installation/usr/local/bin/../libexec/gcc/aarch64-unknown-linux-gnu/13.0.1/collect2
-plugin
/home/alarm/gcc-installation/usr/local/bin/../libexec/gcc/aarch64-unknown-linux-gnu/13.0.1/liblto_plugin.so
-plugin-opt=/home/alarm/gcc-installation/usr/local/bin/../libexec/gcc/aarch64-unknown-linux-gnu/13.0.1/lto-wrapper
-plugin-opt=-fresolution=/tmp/ccup8iGA.res -plugin-opt=-pass-through=-lgcc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s
--eh-frame-hdr -dynamic-linker /lib/ld-linux-aarch64.so.1 -X -EL -maarch64linux
/lib/crt1.o /lib/crti.o
/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/crtbegin.o
-L/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/aarch64-unknown-linux-gnu/13.0.1
-L/home/alarm/gcc-installation/usr/local/bin/../lib/gcc
-L/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/../../../../lib64
-L/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/../../..
/tmp/ccTu98hj.o -lgcc --push-state --as-needed -lgcc_s --pop-state -lc -lgcc
--push-state --as-needed -lgcc_s --pop-state
/home/alarm/gcc-installation/usr/local/bin/../lib/gcc/aarch64-unknown-linux-gnu/13.0.1/crtend.o
/lib/crtn.o
COLLECT_GCC_OPTIONS='-v' '-mlittle-endian' '-mabi=lp64' '-dumpdir' 'a.'
git bisect revealed this is a regression caused by commit
5edf02ed2b6de024f83a023d046a6a18f645bc83.
