Look at phis in ReplaceUsesDominatedBy.

When the instruction does not dominate the phi, but the instruction
that it is replacing does by being an input, do the replacement.

It was a missed improvement opportunity before, but the String.<init>
handling in the builder needs it for correctness.

bug: 111758226
Test: 563-checker-fakestring
Change-Id: I37f01e1aabc2a1f60e21fc57728f07248adbc946

1 files changed, 9 insertions, 0 deletions

diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index 8f822cce5a..79a7e2c858 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -1301,6 +1301,15 @@ void HInstruction::ReplaceUsesDominatedBy(HInstruction* dominator, HInstruction*
     ++it;
     if (dominator->StrictlyDominates(user)) {
       user->ReplaceInput(replacement, index);
+    } else if (user->IsPhi() && !user->AsPhi()->IsCatchPhi()) {
+      // If the input flows from a block dominated by `dominator`, we can replace it.
+      // We do not perform this for catch phis as we don't have control flow support
+      // for their inputs.
+      const ArenaVector<HBasicBlock*>& predecessors = user->GetBlock()->GetPredecessors();
+      HBasicBlock* predecessor = predecessors[index];
+      if (dominator->GetBlock()->Dominates(predecessor)) {
+        user->ReplaceInput(replacement, index);
+      }
     }
   }
 }