ARM: Avoid duplicate vmla when merging vmul and vadd

Avoid generating duplicate vmla instructions for vmul/vadd sequences where the
vmul has more than one use.

For example: function f(a, b, c) { return (a * b) + c + (a * b); }

Previously, this would produce a vmul for the subexpression (a * b), then vmla
for (a * b) + c, then vmla for (a * b) + [(a * b) + c].

Now it produces vmul, vadd, vadd, as expected.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/323423003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21899 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/lithium-arm.cc

@@ -1500,7 +1500,7 @@ LInstruction* LChunkBuilder::DoMul(HMul* instr) {
     return DefineAsRegister(mul);
 
   } else if (instr->representation().IsDouble()) {
-    if (instr->UseCount() == 1 && (instr->uses().value()->IsAdd() ||
+    if (instr->HasOneUse() && (instr->uses().value()->IsAdd() ||
                                instr->uses().value()->IsSub())) {
       HBinaryOperation* use = HBinaryOperation::cast(instr->uses().value());
 
@@ -1547,7 +1547,7 @@ LInstruction* LChunkBuilder::DoSub(HSub* instr) {
     }
     return result;
   } else if (instr->representation().IsDouble()) {
-    if (instr->right()->IsMul()) {
+    if (instr->right()->IsMul() && instr->right()->HasOneUse()) {
       return DoMultiplySub(instr->left(), HMul::cast(instr->right()));
     }
 
@@ -1618,12 +1618,12 @@ LInstruction* LChunkBuilder::DoAdd(HAdd* instr) {
     LInstruction* result = DefineAsRegister(add);
     return result;
   } else if (instr->representation().IsDouble()) {
-    if (instr->left()->IsMul()) {
+    if (instr->left()->IsMul() && instr->left()->HasOneUse()) {
       return DoMultiplyAdd(HMul::cast(instr->left()), instr->right());
     }
 
-    if (instr->right()->IsMul()) {
-      ASSERT(!instr->left()->IsMul());
+    if (instr->right()->IsMul() && instr->right()->HasOneUse()) {
+      ASSERT(!instr->left()->IsMul() || !instr->left()->HasOneUse());
       return DoMultiplyAdd(HMul::cast(instr->right()), instr->left());
     }
 

src/hydrogen-instructions.cc

@@ -1581,7 +1581,7 @@ HValue* HUnaryMathOperation::Canonicalize() {
           val, representation(), false, false));
     }
   }
-  if (op() == kMathFloor && value()->IsDiv() && value()->UseCount() == 1) {
+  if (op() == kMathFloor && value()->IsDiv() && value()->HasOneUse()) {
     HDiv* hdiv = HDiv::cast(value());
 
     HValue* left = hdiv->left();
@@ -2149,7 +2149,7 @@ void InductionVariableData::ChecksRelatedToLength::UseNewIndexInCurrentBlock(
   added_index()->SetOperandAt(1, index_base);
   added_index()->SetOperandAt(2, added_constant());
   first_check_in_block()->SetOperandAt(0, added_index());
-  if (previous_index->UseCount() == 0) {
+  if (previous_index->HasNoUses()) {
     previous_index->DeleteAndReplaceWith(NULL);
   }
 }
@@ -2893,7 +2893,7 @@ bool HConstant::EmitAtUses() {
     // TODO(titzer): this seems like a hack that should be fixed by custom OSR.
     return true;
   }
-  if (UseCount() == 0) return true;
+  if (HasNoUses()) return true;
   if (IsCell()) return false;
   if (representation().IsDouble()) return false;
   if (representation().IsExternal()) return false;

src/hydrogen-instructions.h

@@ -663,6 +663,9 @@ class HValue : public ZoneObject {
   void DeleteAndReplaceWith(HValue* other);
   void ReplaceAllUsesWith(HValue* other);
   bool HasNoUses() const { return use_list_ == NULL; }
+  bool HasOneUse() const {
+    return use_list_ != NULL && use_list_->tail() == NULL;
+  }
   bool HasMultipleUses() const {
     return use_list_ != NULL && use_list_->tail() != NULL;
   }
@@ -3760,7 +3763,7 @@ class HBinaryOperation : public HTemplateInstruction<3> {
     // Otherwise, if there is only one use of the right operand, it would be
     // better off on the left for platforms that only have 2-arg arithmetic
     // ops (e.g ia32, x64) that clobber the left operand.
-    return right()->UseCount() == 1;
+    return right()->HasOneUse();
   }
 
   HValue* BetterLeftOperand() {

src/mips/lithium-mips.cc

@@ -1492,7 +1492,7 @@ LInstruction* LChunkBuilder::DoMul(HMul* instr) {
 
   } else if (instr->representation().IsDouble()) {
     if (kArchVariant == kMips32r2) {
-      if (instr->UseCount() == 1 && instr->uses().value()->IsAdd()) {
+      if (instr->HasOneUse() && instr->uses().value()->IsAdd()) {
         HAdd* add = HAdd::cast(instr->uses().value());
         if (instr == add->left()) {
           // This mul is the lhs of an add. The add and mul will be folded