https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96692
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Roger Sayle <sa...@gcc.gnu.org>: https://gcc.gnu.org/g:d458c53a6f37c8c49aa854d12e6867b4d914555f commit r13-1507-gd458c53a6f37c8c49aa854d12e6867b4d914555f Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Tue Jul 5 17:55:53 2022 +0100 PR rtl-optimization/96692: ((A|B)^C)^A using andn with -mbmi on x86. This patch addresses PR rtl-optimization/96692 on x86_64, by providing a set of combine splitters to convert the three operation ((A|B)^C)^D into a two operation sequence using andn when either A or B is the same register as C or D. This is essentially a reassociation problem that's only a win if the target supports an and-not instruction (as with -mbmi). Hence for the new test case: int f(int a, int b, int c) { return (a ^ b) ^ (a | c); } GCC on x86_64-pc-linux-gnu wth -O2 -mbmi would previously generate: xorl %edi, %esi orl %edx, %edi movl %esi, %eax xorl %edi, %eax ret but with this patch now generates: andn %edx, %edi, %eax xorl %esi, %eax ret 2022-07-05 Roger Sayle <ro...@nextmovesoftware.com> Uroš Bizjak <ubiz...@gmail.com> gcc/ChangeLog PR rtl-optimization/96692 * config/i386/i386.md (define_split): Split ((A | B) ^ C) ^ D as (X & ~Y) ^ Z on target BMI when either C or D is A or B. gcc/testsuite/ChangeLog PR rtl-optimization/96692 * gcc.target/i386/bmi-andn-4.c: New test case.
