https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98954
--- Comment #7 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:418b71c0d535bf91df78bad2e198c57934682eaa commit r13-2048-g418b71c0d535bf91df78bad2e198c57934682eaa Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Mon Aug 15 17:39:47 2022 +0100 PR tree-optimization/64992: (B << 2) != 0 is B when B is Boolean. This patch resolves both PR tree-optimization/64992 and PR tree-optimization/98956 which are missed optimization enhancement request, for which Andrew Pinski already has a proposed solution (related to a fix for PR tree-optimization/98954). Yesterday, I proposed an alternate improved patch for PR98954, which although superior in most respects, alas didn't address this case [which doesn't include a BIT_AND_EXPR], hence this follow-up fix. For many functions, F(B), of a (zero-one) Boolean value B, the expression F(B) != 0 can often be simplified to just B. Hence "(B * 5) != 0" is B, "-B != 0" is B, "bswap(B) != 0" is B, "(B >>r 3) != 0" is B. These are all currently optimized by GCC, with the strange exception of left shifts by a constant (possibly due to the undefined/implementation defined behaviour when the shift constant is larger than the first operand's precision). This patch adds support for this particular case, when the shift constant is valid. 2022-08-15 Roger Sayle <ro...@nextmovesoftware.com> gcc/ChangeLog PR tree-optimization/64992 PR tree-optimization/98956 * match.pd (ne (lshift @0 @1) 0): Simplify (X << C) != 0 to X when X is zero_one_valued_p and the shift constant C is valid. (eq (lshift @0 @1) 0): Likewise, simplify (X << C) == 0 to !X when X is zero_one_valued_p and the shift constant C is valid. gcc/testsuite/ChangeLog PR tree-optimization/64992 * gcc.dg/pr64992.c: New test case.
