https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83234
Bug ID: 83234
Summary: Aggressive loop optim warning for loop iteration that
cannot happen
Product: gcc
Version: 6.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: ketan.surender at gmail dot com
Target Milestone: ---
Created attachment 42759
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42759&action=edit
Reproduction File
I have an example program with the code:
for (j = 0; j < 3; j++) {
for (i = 1; i <= 3 - j; i++) {
out8[i - 1][j] = (int8_T)(i + j);
}
for (i = 4 - j; i < 4; i++) {
out8[i - 1][j] = in15[(i + j) - 3];
}
}
that produces the warning
hankel_script.c: In function ‘hankel_script’:
hankel_script.c:235:32: warning: iteration 2147483644 invokes undefined
behavior [-Waggressive-loop-optimizations]
out8[i - 1][j] = in15[(i + j) - 3];
~~~^~~~
hankel_script.c:234:5: note: within this loop
for (i = 4 - j; i < 4; i++) {
The loop bounds have been defined with constants such that iteration 2147483644
cannot happen.
Repro:
gcc -c -O2 hankel_script.i
I do not see the warning with -O3 or -O1.
My gcc version is 6.3. See details below. I am able to reproduce this using
x86-64 gcc 7.2 on https://gcc.godbolt.org/.
COLLECT_GCC=gcc
Target: x86_64-pc-linux-gnu
Configured with: [SCRUB]/sources/gcc-6.3/configure
--with-gmp=[SCRUB]/gcc-6.3/gmp-4.3 --with-mpfr=[SCRUB]/gcc-6.3/mpfr
--with-mpc=[SCRUB]/gcc-6.3/mpc --enable-languages=c,c++,fortran
--with-bugurl=[SCRUB],_Debugging --enable-shared --enable-linker-build-id
--enable-plugin --enable-checking=release --enable-multiarch --enable-gold
--enable-ld=default --prefix=[SCRUB]/gcc-6.3.0 --with-pkgversion='MW GCC
6.3.0-GLIBC2.11' --with-tune=generic --with-system-zlib --enable-multilib
--with-multilib-list=m32,m64 --with-arch-directory=amd64 --with-arch-32=i586
--with-abi=m64
gcc version 6.3.0 (MW GCC 6.3.0-GLIBC2.11)
