Opt compiler: enhance gvn for commutative ops.

Change-Id: I415b50d58b30cab4ec38077be22373eb9598ec40

1 files changed, 9 insertions, 0 deletions

diff --git a/compiler/optimizing/gvn.cc b/compiler/optimizing/gvn.cc
index cb448c883f..ea65dc0780 100644
--- a/compiler/optimizing/gvn.cc
+++ b/compiler/optimizing/gvn.cc
@@ -299,8 +299,17 @@ void GlobalValueNumberer::VisitBasicBlock(HBasicBlock* block) {
     // Save the next instruction in case `current` is removed from the graph.
     HInstruction* next = current->GetNext();
     if (current->CanBeMoved()) {
+      if (current->IsBinaryOperation() && current->AsBinaryOperation()->IsCommutative()) {
+        // For commutative ops, (x op y) will be treated the same as (y op x)
+        // after fixed ordering.
+        current->AsBinaryOperation()->OrderInputs();
+      }
       HInstruction* existing = set->Lookup(current);
       if (existing != nullptr) {
+        // This replacement doesn't make more OrderInputs() necessary since
+        // current is either used by an instruction that it dominates,
+        // which hasn't been visited yet due to the order we visit instructions.
+        // Or current is used by a phi, and we don't do OrderInputs() on a phi anyway.
         current->ReplaceWith(existing);
         current->GetBlock()->RemoveInstruction(current);
       } else {