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Unfortunately, my latest tree-ssa-math-opts.c patch broke the following testcase. The problem is that the code is adding .ADD_OVERFLOW or .SUB_OVERFLOW before or after the stmt on which the function has been called, which is normally a addition or subtraction that has all the operands. But in the a > ~b optimization that stmt is the ~b stmt and the other comparison operand might be defined only after that ~b stmt, so we can't insert the .ADD_OVERFLOW next to ~b that we want to delete, but need to insert it before the a > temp comparison that uses it; and in that case when removing the BIT_NOT_EXPR stmt we need to ensure the caller doesn't do gsi_next because gsi_remove already points the iterator to the next stmt. 2020-12-13 Jakub Jelinek <jakub@redhat.com> PR tree-optimization/98256 * tree-ssa-math-opts.c (match_uaddsub_overflow): For BIT_NOT_EXPR, only handle a single use, and insert .ADD_OVERFLOW before the comparison rather than after the BIT_NOT_EXPR. Return true iff it is BIT_NOT_EXPR and it has been removed. (math_opts_dom_walker::after_dom_children) <case BIT_NOT_EXPR>: If match_uaddsub_overflow returned true, continue instead of break. * gcc.c-torture/compile/pr98256.c: New test.
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