On Tue, Jul 18, 2017 at 5:50 AM, Christophe Lyon <christophe.l...@linaro.org> wrote: > Hello, > > I've received a complaint that GCC for AArch64 would generate > vectorized code relying on unaligned memory accesses even when using > -mstrict-align. This is a problem for code where such accesses lead to > memory faults. > > A previous patch (r243333) introduced > aarch64_builtin_support_vector_misalignment, which rejects such > accesses when the element size is 64 bits, and accept them otherwise, > which I think it shouldn't. The testcase added at that time only used > 64 bits elements, and therefore didn't fully test the patch. > > The report I received is about vectorized accesses to an array of > unsigned chars, whose start address is not aligned on a 128 bits > boundary. > > The attached patch fixes the problem by making > aarch64_builtin_support_vector_misalignment always return false when > the misalignment is not known at compile time. > > I've also added a testcase, which tries to check if the array start > address alignment is checked (using %16, and-ing with #15), so that > loop peeling is performed *before* using vectorized accesses. Without > the patch, vectorized accesses are used at the beginning of the array, > and byte accesses are used for the remainder at the end, and there is > not such 'and wX,wX,15'. > > BTW, I'm not sure about the same hook for arm... it seems to me it has > a similar problem. > > OK?
I would keep part of the comment: - /* Misalignment factor is unknown at compile time but we know - it's word aligned. */ Something like: /* Misalignment factor is unknown at compile time. */ Otherwise it is not obvious what -1 means. Other than I think this patch is good (I cannot approve though). Thanks, Andrew > > Thanks, > > Christophe
