On Tue, Feb 1, 2022 at 9:57 AM Roger Sayle <ro...@nextmovesoftware.com> wrote: > > > 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. > > > This patch has been tested on x86_64-pc-linux-gnu with make bootstrap > and make -k check with no new failures. Ok for mainline?
OK for trunk. Thanks, Richard. > > 2022-02-01 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. > > > Thanks in advance (and Happy Chinese New Year), > Roger > -- >
