https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85989
Bug ID: 85989
Summary: Incorrect result for example involving unary minus in
a loop
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 44208
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44208&action=edit
Preprocessed reproduction file
Please see the attached file 'standalone.i'. When I run this in -O0 I see the
result
gcc -Wall -Wstrict-aliasing=0 -O0 standalone.i -o standalone
./standalone
--> 0
--> 0
This is what I expect. If I compile with '-O1' I see
gcc -Wall -Wstrict-aliasing=0 -O1 standalone.i -o standalone
./standalone
--> 8
--> 8
Which is unexpected. I poked around in gdb and stared at the asm in godbolt and
it seems like the negation is being omitted in the following loop:
for (b_P5 = 0; b_P5 < 8; b_P5++) {
P26 = P29;
P29 = -(int)*P5;
}
Here is my gcc info
Using built-in specs.
COLLECT_GCC=[SNIP]/glnxa64/gcc-6.3.0/bin/gcc
COLLECT_LTO_WRAPPER=[SNIP]/glnxa64/gcc-6.3.0/bin/../libexec/gcc/x86_64-pc-linux-gnu/6.3.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: [SNIP]/sources/gcc-6.3/configure
--with-gmp=[SNIP]/glnxa64/gcc-6.3/gmp-4.3 --with-mpfr=[SNIP]/gcc-6.3/mpfr
--with-mpc=[SNIP]/gcc-6.3/mpc --enable-languages=c,c++,fortran
--with-bugurl=[SNIP],_Debugging --enable-shared --enable-linker-build-id
--enable-plugin --enable-checking=release --enable-multiarch --enable-gold
--enable-ld=default --enable-libstdcxx-time=no
--prefix=[SNIP]/glnxa64/gcc-6.3.0 --with-pkgversion='MW GCC 6.3.0-GLIBC2.12'
--with-tune=generic --with-system-zlib --enable-multilib
--with-multilib-list=m32,m64 --with-arch-directory=amd64 --with-arch-32=i586
--with-abi=m64
Thread model: posix
gcc version 6.3.0 (MW GCC 6.3.0-GLIBC2.12)
