On 12 September 2013 12:47, Richard Biener <richard.guent...@gmail.com> wrote: > Look at the -fdump-tree-vect-details, it should print what it does during > alignment analysis. Then debug the code ...
OK, I think I got to the bottom of this. It's not the vectorizer fault after all. Jakub was right to point out that there is checking code inserted (except that it was for versioning, not peeling). I didn't investigate at first this because I saw the faulty access actually happening (and I found it very suspicious that we generate code that couldn't be correct). The issue is that I am using super-block scheduling in sched2 and that my sched_reorder hook prioritized the load operation over the conditional branch that did the alignment check. I'm now leaning toward a scheduler bug (or my customization thereof). I expect superblock scheduling to hoist instructions out of their original basic-block, but it seems very dangerous to move memory accesses this way (without speculation). Is it my hook's job to ensure this reordering doesn't happen? I'd think the memory access shouldn't be in the ready list in the first place. Fred
