https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57359
--- Comment #24 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #22)
> Created attachment 48311 [details]
> patch
>
> Note that apart from the possible bad impact on optimization when fixing this
> bug an actual fix is complicated by the custom "optimized" dependence
> analysis
> code in the loop invariant motion pass.
>
> A conservative "simple" patch would be the attached but that doesn't preserve
> store-motion for the following (because the LIM data dependence code doesn't
> care about stmt order):
>
> typedef int A;
> typedef float B;
>
> void __attribute__((noinline,noclone))
> foo(A *p, B *q, long unk)
> {
> for (long i = 0; i < unk; ++i) {
> q[i] = 42;
> *p = 1;
> }
> }
>
> usually this bug doesn't manifest itself but of course the fix will be
> experienced everywhere. Benchmarking the simple patch might reveal
> it's not an issue (but I doubt that...).
One case like this is gcc.dg/tree-ssa/pr81744.c which fails after the patch
because we do not SM the global induction variable update which is already
last before exit. Similarly gcc.dg/graphite/pr80906.c and
gcc.target/i386/pr64110.c - that's all of the GCC testsuite fallout on x86_64.
I do not
think those regressions are acceptable on its own but I'll throw the patch
on SPEC CPU 2006 to get more data (I fear even a solution preserving the
cited regressions will regress actual code too much).
