Better handling of Phi nodes with constant inputs

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
diff --git a/src/hydrogen-instructions.cc b/src/hydrogen-instructions.cc
index d6710a4fa1f43b9311f416c5e5604c46f4322832..5f0cd9d3176e1327269cc5bdfdd6e47cba7372b5 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -2264,7 +2264,8 @@ Representation HBinaryOperation::RepresentationFromInputs() {
 
 
 void HBinaryOperation::AssumeRepresentation(Representation r) {
-  set_observed_input_representation(r, r);
+  set_observed_input_representation(1, r);
+  set_observed_input_representation(2, r);
   HValue::AssumeRepresentation(r);
 }
 
@@ -3462,6 +3463,42 @@ void HBitwise::PrintDataTo(StringStream* stream) {
 }
 
 
+void HPhi::SimplifyConstantInputs() {
+  // Convert constant inputs to integers when all uses are truncating.
+  // This must happen before representation inference takes place.
+  if (!CheckUsesForFlag(kTruncatingToInt32)) return;
+  for (int i = 0; i < OperandCount(); ++i) {
+    if (!OperandAt(i)->IsConstant()) return;
+  }
+  HGraph* graph = block()->graph();
+  for (int i = 0; i < OperandCount(); ++i) {
+    HConstant* operand = HConstant::cast(OperandAt(i));
+    if (operand->HasInteger32Value()) {
+      continue;
+    } else if (operand->HasDoubleValue()) {
+      HConstant* integer_input =
+          new(graph->zone()) HConstant(DoubleToInt32(operand->DoubleValue()),
+                                       Representation::Integer32());
+      integer_input->InsertAfter(operand);
+      SetOperandAt(i, integer_input);
+    } else if (operand == graph->GetConstantTrue()) {
+      SetOperandAt(i, graph->GetConstant1());
+    } else {
+      // This catches |false|, |undefined|, strings and objects.
+      SetOperandAt(i, graph->GetConstant0());
+    }
+  }
+  // Overwrite observed input representations because they are likely Tagged.
+  for (HUseIterator it(uses()); !it.Done(); it.Advance()) {
+    HValue* use = it.value();
+    if (use->IsBinaryOperation()) {
+      HBinaryOperation::cast(use)->set_observed_input_representation(
+          it.index(), Representation::Integer32());
+    }
+  }
+}
+
+
 void HPhi::InferRepresentation(HInferRepresentation* h_infer) {
   ASSERT(CheckFlag(kFlexibleRepresentation));
   // If there are non-Phi uses, and all of them have observed the same