Consistently assume that arithmetic operations can overflow unless one can prove the opposite.

Previously, HDiv never had its CanOverflow flag cleared and HMod had
inverted logic (compared to HAdd, HSub and HMul). Minor cleanups on the way.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/14617015

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14644 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.cc

@@ -1445,6 +1445,16 @@ HValue* HMul::Canonicalize() {
 }
 
 
+HValue* HMod::Canonicalize() {
+  return this;
+}
+
+
+HValue* HDiv::Canonicalize() {
+  return this;
+}
+
+
 HValue* HChange::Canonicalize() {
   return (from().Equals(to())) ? value() : this;
 }
@@ -1773,20 +1783,22 @@ Range* HMul::InferRange(Zone* zone) {
 
 Range* HDiv::InferRange(Zone* zone) {
   if (representation().IsInteger32()) {
+    Range* a = left()->range();
+    Range* b = right()->range();
     Range* result = new(zone) Range();
-    if (left()->range()->CanBeMinusZero()) {
+    if (a->CanBeMinusZero()) {
       result->set_can_be_minus_zero(true);
     }
 
-    if (left()->range()->CanBeZero() && right()->range()->CanBeNegative()) {
+    if (a->CanBeZero() && b->CanBeNegative()) {
       result->set_can_be_minus_zero(true);
     }
 
-    if (right()->range()->Includes(-1) && left()->range()->Includes(kMinInt)) {
-      SetFlag(HValue::kCanOverflow);
+    if (!a->Includes(kMinInt) || !b->Includes(-1)) {
+      ClearFlag(HValue::kCanOverflow);
     }
 
-    if (!right()->range()->CanBeZero()) {
+    if (!b->CanBeZero()) {
       ClearFlag(HValue::kCanBeDivByZero);
     }
     return result;
@@ -1799,16 +1811,17 @@ Range* HDiv::InferRange(Zone* zone) {
 Range* HMod::InferRange(Zone* zone) {
   if (representation().IsInteger32()) {
     Range* a = left()->range();
+    Range* b = right()->range();
     Range* result = new(zone) Range();
     if (a->CanBeMinusZero() || a->CanBeNegative()) {
       result->set_can_be_minus_zero(true);
     }
 
-    if (right()->range()->Includes(-1) && left()->range()->Includes(kMinInt)) {
-      SetFlag(HValue::kCanOverflow);
+    if (!a->Includes(kMinInt) || !b->Includes(-1)) {
+      ClearFlag(HValue::kCanOverflow);
     }
 
-    if (!right()->range()->CanBeZero()) {
+    if (!b->CanBeZero()) {
       ClearFlag(HValue::kCanBeDivByZero);
     }
     return result;

src/hydrogen-instructions.h

@@ -4414,6 +4414,8 @@ class HMod: public HArithmeticBinaryOperation {
 
   virtual HValue* EnsureAndPropagateNotMinusZero(BitVector* visited);
 
+  virtual HValue* Canonicalize();
+
   DECLARE_CONCRETE_INSTRUCTION(Mod)
 
  protected:
@@ -4425,6 +4427,7 @@ class HMod: public HArithmeticBinaryOperation {
   HMod(HValue* context, HValue* left, HValue* right)
       : HArithmeticBinaryOperation(context, left, right) {
     SetFlag(kCanBeDivByZero);
+    SetFlag(kCanOverflow);
   }
 };
 
@@ -4448,6 +4451,8 @@ class HDiv: public HArithmeticBinaryOperation {
 
   virtual HValue* EnsureAndPropagateNotMinusZero(BitVector* visited);
 
+  virtual HValue* Canonicalize();
+
   DECLARE_CONCRETE_INSTRUCTION(Div)
 
  protected: