Better handling of Phi nodes with constant inputs

Review URL: https://codereview.chromium.org/14471034

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14448 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

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

src/hydrogen-instructions.h

@@ -3143,6 +3143,8 @@ class HPhi: public HValue {
     return true;
   }
 
+  void SimplifyConstantInputs();
+
  protected:
   virtual void DeleteFromGraph();
   virtual void InternalSetOperandAt(int index, HValue* value) {
@@ -3444,10 +3446,9 @@ class HBinaryOperation: public HTemplateInstruction<3> {
     return right();
   }
 
-  void set_observed_input_representation(Representation left,
-                                         Representation right) {
-    observed_input_representation_[0] = left;
-    observed_input_representation_[1] = right;
+  void set_observed_input_representation(int index, Representation rep) {
+    ASSERT(index >= 1 && index <= 2);
+    observed_input_representation_[index - 1] = rep;
   }
 
   virtual void initialize_output_representation(Representation observed) {

src/hydrogen.cc

@@ -3747,7 +3747,12 @@ void HInferRepresentation::Analyze() {
     }
   }
 
-  // (3a) Use the phi reachability information from step 2 to
+  // Simplify constant phi inputs where possible.
+  for (int i = 0; i < phi_count; ++i) {
+    phi_list->at(i)->SimplifyConstantInputs();
+  }
+
+  // Use the phi reachability information from step 2 to
   // push information about values which can't be converted to integer
   // without deoptimization through the phi use-def chains, avoiding
   // unnecessary deoptimizations later.
@@ -3764,7 +3769,7 @@ void HInferRepresentation::Analyze() {
     }
   }
 
-  // (3b) Use the phi reachability information from step 2 to
+  // Use the phi reachability information from step 2 to
   // sum up the non-phi use counts of all connected phis.
   for (int i = 0; i < phi_count; ++i) {
     HPhi* phi = phi_list->at(i);
@@ -9686,7 +9691,8 @@ void HOptimizedGraphBuilder::VisitSub(UnaryOperation* expr) {
     info = TypeInfo::Unknown();
   }
   if (instr->IsBinaryOperation()) {
-    HBinaryOperation::cast(instr)->set_observed_input_representation(rep, rep);
+    HBinaryOperation::cast(instr)->set_observed_input_representation(1, rep);
+    HBinaryOperation::cast(instr)->set_observed_input_representation(2, rep);
   }
   return ast_context()->ReturnInstruction(instr, expr->id());
 }
@@ -10127,7 +10133,8 @@ HInstruction* HOptimizedGraphBuilder::BuildBinaryOperation(
 
   if (instr->IsBinaryOperation()) {
     HBinaryOperation* binop = HBinaryOperation::cast(instr);
-    binop->set_observed_input_representation(left_rep, right_rep);
+    binop->set_observed_input_representation(1, left_rep);
+    binop->set_observed_input_representation(2, right_rep);
     binop->initialize_output_representation(result_rep);
   }
   return instr;
@@ -10507,7 +10514,8 @@ void HOptimizedGraphBuilder::VisitCompareOperation(CompareOperation* expr) {
     if (combined_rep.IsTagged() || combined_rep.IsNone()) {
       HCompareGeneric* result =
           new(zone()) HCompareGeneric(context, left, right, op);
-      result->set_observed_input_representation(left_rep, right_rep);
+      result->set_observed_input_representation(1, left_rep);
+      result->set_observed_input_representation(2, right_rep);
       result->set_position(expr->position());
       return ast_context()->ReturnInstruction(result, expr->id());
     } else {