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Re: [PATCH] Fix optimize_range_tests_diff
- From: Jeff Law <law at redhat dot com>
- To: Jakub Jelinek <jakub at redhat dot com>, Richard Biener <rguenther at suse dot de>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Tue, 14 Oct 2014 11:23:22 -0600
- Subject: Re: [PATCH] Fix optimize_range_tests_diff
- Authentication-results: sourceware.org; auth=none
- References: <20141014160219 dot GF10376 at tucnak dot redhat dot com>
On 10/14/14 10:02, Jakub Jelinek wrote:
When hacking on range reassoc opt, I've noticed we can emit
code with undefined behavior even when there wasn't one originally,
in particular for:
(X - 43U) <= 3U || (X - 75U) <= 3U
and this loop can transform that into
((X - 43U) & ~(75U - 43U)) <= 3U. */
we actually don't transform it to what the comment says, but
((X - 43) & ~(75U - 43U)) <= 3U
i.e. the initial subtraction can be performed in signed type,
if in here X is e.g. INT_MIN or INT_MIN + 42, the subtraction
at gimple level would be UB (not caught by -fsanitize=undefined,
because that is handled much earlier).
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2014-10-14 Jakub Jelinek <firstname.lastname@example.org>
* tree-ssa-reassoc.c (optimize_range_tests_diff): Perform
MINUS_EXPR in unsigned type to avoid undefined behavior.
Any chance this fixes: