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As the following testcases show (the first one reported, last two found by code inspection), we need to disallow side-effects in simplifications that turn some unconditional expression into conditional one. From my little understanding of genmatch.c, it is able to automatically disallow side effects if the same operand is used multiple times in the match pattern, maybe if it is used multiple times in the replacement pattern, and if it is used in conditional contexts in the match pattern, could it be taught to handle this case too? If yes, perhaps just the first hunk could be usable for 8/9 backports (+ the testcases). 2020-02-15 Jakub Jelinek <jakub@redhat.com> PR tree-optimization/93744 * match.pd (((m1 >/</>=/<= m2) * d -> (m1 >/</>=/<= m2) ? d : 0, A - ((A - B) & -(C cmp D)) -> (C cmp D) ? B : A, A + ((B - A) & -(C cmp D)) -> (C cmp D) ? B : A): For GENERIC, make sure @2 in the first and @1 in the other patterns has no side-effects. * gcc.c-torture/execute/pr93744-1.c: New test. * gcc.c-torture/execute/pr93744-2.c: New test. * gcc.c-torture/execute/pr93744-3.c: New test.
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