Bug 876607 - IonMonkey: Reordering of operands should look to real use count, r=sstangl

js/src/ion/Lowering.cpp

@@ -858,7 +858,13 @@ ReorderCommutative(MDefinition **lhsp, MDefinition **rhsp)
     // Ensure that if there is a constant, then it is in rhs.
     // In addition, since clobbering binary operations clobber the left
     // operand, prefer a non-constant lhs operand with no further uses.
-    if (lhs->isConstant() || (!rhs->isConstant() && rhs->useCount() == 1)) {
+
+    if (rhs->isConstant())
+        return;
+
+    if (lhs->isConstant() ||
+        (lhs->defUseCount() == 1 && rhs->defUseCount() != 1))
+    {
         *rhsp = lhs;
         *lhsp = rhs;
     }

js/src/ion/MIR.cpp

@@ -241,6 +241,16 @@ MDefinition::useCount() const
     return count;
 }
 
+size_t
+MDefinition::defUseCount() const
+{
+    size_t count = 0;
+    for (MUseIterator i(uses_.begin()); i != uses_.end(); i++)
+        if ((*i)->consumer()->isDefinition())
+            count++;
+    return count;
+}
+
 MUseIterator
 MDefinition::removeUse(MUseIterator use)
 {

js/src/ion/MIR.h

@@ -441,6 +441,10 @@ class MDefinition : public MNode
     // Number of uses of this instruction.
     size_t useCount() const;
 
+    // Number of uses of this instruction.
+    // (only counting MDefinitions, ignoring MResumePoints)
+    size_t defUseCount() const;
+
     bool hasUses() const {
         return !uses_.empty();
     }