https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93908
--- Comment #3 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:73dc4ae47418aef2eb470b8f71cef57dce37349e commit r10-6844-g73dc4ae47418aef2eb470b8f71cef57dce37349e Author: Jakub Jelinek <ja...@redhat.com> Date: Tue Feb 25 13:56:47 2020 +0100 combine: Fix find_split_point handling of constant store into ZERO_EXTRACT [PR93908] git is miscompiled on s390x-linux with -O2 -march=zEC12 -mtune=z13. I've managed to reduce it into the following testcase. The problem is that during combine we see the s->k = -1; bitfield store and change the SET_SRC from a pseudo into a constant: (set (zero_extract:DI (mem/j:HI (plus:DI (reg/v/f:DI 60 [ s ]) (const_int 10 [0xa])) [0 +0 S2 A16]) (const_int 2 [0x2]) (const_int 7 [0x7])) (const_int -1 [0xffffffffffffffff])) This on s390x with the above option isn't recognized as valid instruction, so find_split_point decides to handle it as IOR or IOR/AND. src is -1, mask is 3 and pos is 7. src != mask (this is also incorrect, we want to set all (both) bits in the bitfield), so we go for IOR/AND, but instead of trying mem = (mem & ~0x180) | ((-1 << 7) & 0x180) we actually try mem = (mem & ~0x180) | (-1 << 7) and that is further simplified into: mem = mem | (-1 << 7) aka mem = mem | 0xff80 which doesn't set just the 2-bit bitfield, but also many other bitfields that shouldn't be touched. We really should do: mem = mem | 0x180 instead. The problem is that we assume that no bits but those low len (2 here) will be set in the SET_SRC, but there is nothing that can prevent that, we just should ignore the other bits. The following patch fixes it by masking src with mask, this way already the src == mask test will DTRT, and as the code for or_mask uses gen_int_mode, if the most significant bit is set after shifting it left by pos, it will be properly sign-extended. 2020-02-25 Jakub Jelinek <ja...@redhat.com> PR rtl-optimization/93908 * combine.c (find_split_point): For store into ZERO_EXTRACT, and src with mask. * gcc.c-torture/execute/pr93908.c: New test.
