https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86438
--- Comment #8 from Alexandre Oliva <aoliva at gcc dot gnu.org> --- Author: aoliva Date: Fri Nov 9 10:16:09 2018 New Revision: 265957 URL: https://gcc.gnu.org/viewcvs?rev=265957&root=gcc&view=rev Log: [PR86438] compare-elim: cope with set of in_b When in_a resolves to a register set in the prev_clobber insn, we may use the SET_SRC for the compare instead. However, when in_b so resolves, we proceed to use the reg with its earlier value. When both resolve to the same register and prev_clobber is an insn that modifies the register, this arrangement may cause the compare to match (when it shouldn't) and the elimination of the compare to incorrectly succeed. (set (reg 1) (plus (reg 1) (const_int N))) (set (reg 2) (reg 1)) (set (reg flags) (compare (reg 1) (reg 2))) in_a: (reg 1) --> (plus (reg 1) (const_int N)) in_b: (reg 2) -> (reg 1) -/> oops (parallel [ (set (reg flags) (compare (plus (reg 1) (const_int N)) (reg 1))) ;; should be (plus...) (set (reg 1) (plus (reg 1) (const_int N)))]) (set (reg 2) (reg 1)) This patch arranges for in_b to also undergo SET_SRC substitution when appropriate, with a shortcut for when in_a and in_b are the same rtx. for gcc/ChangeLog PR rtl-optimization/86438 * compare-elim.c (try_eliminate_compare): Use SET_SRC instead of in_b for the compare if in_b is SET_DEST. for gcc/testsuite/ChangeLog PR rtl-optimization/86438 * gcc.dg/torture/pr86438.c: New. Added: trunk/gcc/testsuite/gcc.dg/torture/pr86438.c Modified: trunk/gcc/ChangeLog trunk/gcc/compare-elim.c trunk/gcc/testsuite/ChangeLog
