https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100499
--- Comment #40 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Richard Biener <rgue...@gcc.gnu.org>: https://gcc.gnu.org/g:0898049ad9bf6c46e510b18aaafca4946802749f commit r12-7052-g0898049ad9bf6c46e510b18aaafca4946802749f Author: Richard Biener <rguent...@suse.de> Date: Wed Jan 26 09:35:57 2022 +0100 tree-optimization/100499 - niter analysis and multiple_of_p niter analysis uses multiple_of_p which currently assumes operations like MULT_EXPR do not wrap. We've got to rely on this for optimizing size expressions like those in DECL_SIZE and those generally use unsigned arithmetic with no indication that they are not expected to wrap. To preserve that the following adds a parameter to multiple_of_p, defaulted to true, indicating that the TOP expression is not expected to wrap for outer computations in TYPE. This mostly follows a patch proposed by Bin last year with the conversion behavior added. Applying to all users the new effect is that upon type conversions in the TOP expression the behavior will switch to honor TYPE_OVERFLOW_UNDEFINED for the converted sub-expressions. The patch also changes the occurance in niter analysis that we know is problematic and we have testcases for to pass false to multiple_of_p. The patch also contains a change to the PR72817 fix from Bin to avoid regressing gcc.dg/tree-ssa/loop-42.c. The intent for stage1 is to introduce a size_multiple_of_p and internalize the added parameter so all multiple_of_p users will honor TYPE_OVERFLOW_UNDEFINED and users dealing with size expressions need to be switched to size_multiple_of_p. 2022-01-26 Richard Biener <rguent...@suse.de> PR tree-optimization/100499 * fold-const.h (multiple_of_p): Add nowrap parameter, defaulted to true. * fold-const.cc (multiple_of_p): Likewise. Honor it for MULT_EXPR, PLUS_EXPR and MINUS_EXPR and pass it along, switching to false for conversions. * tree-ssa-loop-niter.cc (number_of_iterations_ne): Do not claim the outermost expression does not wrap when calling multiple_of_p. Refactor the check done to check the original IV, avoiding a bias that might wrap. * gcc.dg/torture/pr100499-1.c: New testcase. * gcc.dg/torture/pr100499-2.c: Likewise. * gcc.dg/torture/pr100499-3.c: Likewise. Co-authored-by: Bin Cheng <bin.ch...@linux.alibaba.com>
