http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413
Bug ID: 59413 Summary: wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes Product: gcc Version: 4.9.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-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 -Os (but not at the other optimization levels) in both 32-bit and 64-bit modes. It is interesting that the typedef appears necessary to trigger the miscompilation. This is a regression from 4.8.x. $ 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/4.9.0/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 4.9.0 20131206 (experimental) [trunk revision 205734] (GCC) $ $ gcc-trunk -O1 small.c; a.out 7 $ gcc-trunk -O2 small.c; a.out 7 $ gcc-4.8 -Os small.c; a.out 7 $ $ gcc-trunk -Os small.c; a.out 2 $ -------------------------------- int printf (const char *, ...); typedef unsigned int uint32_t; uint32_t a; int b; int main () { uint32_t c; for (a = 7; a <= 1; a++) { char d = a; c = d; b = a == c; } printf ("%d\n", a); return 0; }