tree e9b203d37fb3b6e119eaa97afc11cccbcd2aa20d
parent f14a034634ac7ddc314008e39d62af6ceae0166a
author Nikita Popov <npopov@redhat.com> 1656335364 +0200
committer Nikita Popov <npopov@redhat.com> 1657029720 +0200

[SCEV] Fix isImpliedViaMerge() with values from previous iteration (PR56242)

When trying to prove an implied condition on a phi by proving it
for all incoming values, we need to be careful about values coming
from a backedge, as these may refer to a previous loop iteration.
A variant of this issue was fixed in D101829, but the dominance
condition used there isn't quite right: It checks that the value
dominates the incoming block, which doesn't exclude backedges
(values defined in a loop will usually dominate the loop latch,
which is the incoming block of the backedge).

Instead, we should be checking for domination of the phi block.
Any values defined inside the loop will not dominate the loop
header phi.

Fixes https://github.com/llvm/llvm-project/issues/56242.

Differential Revision: https://reviews.llvm.org/D128640

(cherry picked from commit e4d1d0cc2c9ca38f98bc9b70c3e3db3a18f1e06e)