https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102950
--- Comment #6 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:b3e98eb3396e16ae8b20c94916bc2bd7862d2c97 commit r13-89-gb3e98eb3396e16ae8b20c94916bc2bd7862d2c97 Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Tue May 3 14:38:50 2022 -0400 PR tree-optimization/102950: Improved EVRP for signed BIT_XOR_EXPR. This patch fixes PR tree-optimization/102950, which is a P2 regression, by providing better range bounds for BIT_XOR_EXPR, BIT_AND_EXPR and BIT_IOR_EXPR on signed integer types. In general terms, any binary bitwise operation on sign-extended or zero-extended integer types will produce results that are themselves sign-extended or zero-extended. More precisely, we can derive signed bounds from the number of leading redundant sign bit copies, from the equation: clrsb(X op Y) >= min (clrsb (X), clrsb(Y)) and from the property that for any (signed or unsigned) range [lb, ub] that clrsb([lb, ub]) >= min (clrsb(lb), clrsb(ub)). These can be used to show that [-1, 0] op [-1, 0] is [-1, 0] or that [-128, 127] op [-128, 127] is [-128, 127], even when tracking nonzero bits would result in VARYING (as every bit can be 0 or 1). This is equivalent to determining the minimum type precision in which the operation can be performed then sign extending the result. One additional refinement is to observe that X ^ Y can never be zero if the ranges of X and Y don't overlap, i.e. X can't be equal to Y. Previously, the expression "(int)(char)a ^ 233" in the PR was considered VARYING, but with the above changes now has the range [-256, -1][1, 255], which is sufficient to optimize away the call to foo. 2022-05-03 Roger Sayle <ro...@nextmovesoftware.com> gcc/ChangeLog PR tree-optimization/102950 * range-op.cc (wi_optimize_signed_bitwise_op): New function to determine bounds of bitwise operations on signed types. (operator_bitwise_and::wi_fold): Call the above function. (operator_bitwise_or::wi_fold): Likewise. (operator_bitwise_xor::wi_fold): Likewise. Additionally, the result can't be zero if the operands can't be equal. gcc/testsuite/ChangeLog PR tree-optimization/102950 * gcc.dg/pr102950.c: New test case. * gcc.dg/tree-ssa/evrp10.c: New test case.
