Hi! On Thu, Dec 30, 2021 at 10:43:32AM +0100, Jakub Jelinek wrote: > The following testcase is miscompiled, because a prologue which > contains subq $8, %rsp instruction is emitted at the start of > a basic block which contains conditional jump that depends on > flags register set in an earlier basic block, the prologue instruction > then clobbers those flags. > Normally this case is checked by can_get_prologue predicate, but this > is done only at the start of the loop. If we update pro later in the > loop (because some bb shouldn't be duplicated) and then don't push > anything further into vec and the vec is already empty (this can happen > when the new pro is already in bb_with bitmask and either has no successors > (that is the case in the testcase where that bb ends with a trap) or > all the successors are already in bb_with, then the loop doesn't iterate > further and can_get_prologue will not be checked. > > The following simple patch makes sure we call can_get_prologue even after > the last former iteration when vec is already empty and only break from > the loop afterwards (and only if the updating of pro done because of > !can_get_prologue didn't push anything into vec again). > > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
That looks good, and very simple, thanks! git blame says I wrote 69.9% of shrink-wrap.c, but I am not maintainer of it, so I cannot approve your patch -- but it is fine afaics. Segher > 2021-12-30 Jakub Jelinek <ja...@redhat.com> > > PR rtl-optimization/103860 > * shrink-wrap.c (try_shrink_wrapping): Make sure can_get_prologue is > called on pro even if nothing further is pushed into vec. > > * gcc.dg/pr103860.c: New test.
