https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64756
Bug ID: 64756 Summary: wrong code at -O3 on x86_64-linux-gnu (in 32-bit mode) Product: gcc Version: 5.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: rtl-optimization Assignee: unassigned at gcc dot gnu.org Reporter: su at cs dot ucdavis.edu The current gcc trunk miscompiles the following code on x86_64-linux at -O3 in the 32-bit mode (but not in 64-bit mode). This is a regression from 4.9.x. It is quite strange that the bug seems to be sensitive to the name of the variable "tmp" --- changing the variable to "b" for example will mask it. $ gcc-trunk -v Using built-in specs. COLLECT_GCC=gcc-trunk COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/5.0.0/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk --enable-languages=c,c++ --disable-werror --enable-multilib Thread model: posix gcc version 5.0.0 20150122 (experimental) [trunk revision 220011] (GCC) $ $ gcc-trunk -m32 -O2 small.c; a.out $ gcc-trunk -m64 -O3 small.c; a.out $ gcc-4.9 -m32 -O3 small.c; a.out $ $ gcc-trunk -m32 -O3 small.c $ ./a.out Aborted (core dumped) $ --------------------------------- int a, *tmp, **c = &tmp; volatile int d; static int *volatile *e = &tmp; unsigned int f; static void fn1 (int *p) { int g; for (; f < 1; f++) for (g = 1; g >= 0; g--) { d || d; *c = p; if (tmp != &a) __builtin_abort (); *e = 0; } } int main () { fn1 (&a); return 0; }