Relax the only one back-edge restriction.
The rule is in the way for better register allocation, as
it creates an artificial join point between multiple paths.
Change-Id: Ia4392890f95bcea56d143138f28ddce6c572ad58
diff --git a/compiler/optimizing/ssa_liveness_analysis.h b/compiler/optimizing/ssa_liveness_analysis.h
index 7b98c4e..b550d8a 100644
--- a/compiler/optimizing/ssa_liveness_analysis.h
+++ b/compiler/optimizing/ssa_liveness_analysis.h
@@ -973,7 +973,11 @@
break;
}
- size_t back_edge_use_position = current->GetSingleBackEdge()->GetLifetimeEnd();
+ // We're only adding a synthesized use at the last back edge. Adding syntehsized uses on
+ // all back edges is not necessary: anything used in the loop will have its use at the
+ // last back edge. If we want branches in a loop to have better register allocation than
+ // another branch, then it is the linear order we should change.
+ size_t back_edge_use_position = current->GetLifetimeEnd();
if ((first_use_ != nullptr) && (first_use_->GetPosition() <= back_edge_use_position)) {
// There was a use already seen in this loop. Therefore the previous call to `AddUse`
// already inserted the backedge use. We can stop going outward.