https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99600
--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:d55ce33a34a8e33d17285228b32cf1e564241a70 commit r11-7694-gd55ce33a34a8e33d17285228b32cf1e564241a70 Author: Jakub Jelinek <ja...@redhat.com> Date: Tue Mar 16 18:46:20 2021 +0100 i386: Avoid mutual recursion between two peephole2s [PR99600] As the testcase shows, the compiler hangs and eats all memory when compiling it. This is because in r11-7274-gdecd8fb0128870d0d768ba53dae626913d6d9c54 I have changed the ix86_avoid_lea_for_addr splitting from a splitter into a peephole2 (because during splitting passes we don't have guaranteed df, while during peephole2 we do). The problem is we have another peephole2 that works in the opposite way, when seeing split lea (in particular ASHIFT followed by PLUS) it attempts to turn it back into a lea. In the past, they were fighting against each other, but as they were in different passes, simply the last one won. So, split after reload split the lea into shift left and plus, peephole2 reverted that (but, note not perfectly, the peephole2 doesn't understand that something can be placed into lea disp; to be fixed for GCC12) and then another split pass split the lea appart again. But my changes and the way peephole2 works means that we endlessly iterate over those two, the first peephole2 splits the lea, the second one reverts it, the first peephole2 splits the new lea back into new 2 insns and so forth forever. So, we need to break the cycle somehow. This patch does that by not emitting an ASHIFT insn from ix86_split_lea_for_addr but emitting a corresponding MULT by constant instead, and splitting that later back into ASHIFT. 2021-03-16 Jakub Jelinek <ja...@redhat.com> PR target/99600 * config/i386/i386-expand.c (ix86_split_lea_for_addr): Emit a MULT rather than ASHIFT. * config/i386/i386.md (mult by 1248 into ashift): New splitter. * gcc.target/i386/pr99600.c: New test.
