Bug 781368 - Fold TypeOf strings in MConstant. r=efaust

js/src/ion/Lowering.cpp

@@ -339,6 +339,24 @@ LIRGenerator::visitTest(MTest *test)
     if (opd->type() == MIRType_Object)
         return add(new LGoto(ifTrue));
 
+    // Constant Double operand.
+    if (opd->type() == MIRType_Double && opd->isConstant()) {
+        double dbl = opd->toConstant()->value().toDouble();
+        return add(new LGoto(dbl ? ifTrue : ifFalse));
+    }
+
+    // Constant Int32 operand.
+    if (opd->type() == MIRType_Int32 && opd->isConstant()) {
+        int32 num = opd->toConstant()->value().toInt32();
+        return add(new LGoto(num ? ifTrue : ifFalse));
+    }
+
+    // Constant Boolean operand.
+    if (opd->type() == MIRType_Boolean && opd->isConstant()) {
+        bool result = opd->toConstant()->value().toBoolean();
+        return add(new LGoto(result ? ifTrue : ifFalse));
+    }
+
     // Check if the operand for this test is a compare operation. If it is, we want
     // to emit an LCompare*AndBranch rather than an LTest*AndBranch, to fuse the
     // compare and jump instructions.

js/src/ion/MIR.cpp

@@ -11,6 +11,7 @@
 #include "MIRGraph.h"
 #include "EdgeCaseAnalysis.h"
 #include "jsnum.h"
+#include "jsstr.h"
 #include "jstypedarrayinlines.h" // For ClampIntForUint8Array
 
 using namespace js;
@@ -1347,6 +1348,43 @@ MCompare::evaluateConstantOperands(bool *result)
     Value lhs = left->toConstant()->value();
     Value rhs = right->toConstant()->value();
 
+    // Fold away some String equality comparisons.
+    if (lhs.isString() && rhs.isString()) {
+        int32_t comp = 0; // Default to equal.
+        if (left != right) {
+            if (!CompareStrings(GetIonContext()->cx, lhs.toString(), rhs.toString(), &comp))
+                return false;
+        }
+        
+        switch (jsop_) {
+          case JSOP_LT:
+            *result = (comp < 0);
+            break;
+          case JSOP_LE:
+            *result = (comp <= 0);
+            break;
+          case JSOP_GT:
+            *result = (comp > 0);
+            break;
+          case JSOP_GE:
+            *result = (comp >= 0);
+            break;
+          case JSOP_STRICTEQ: // Fall through.
+          case JSOP_EQ:
+            *result = (comp == 0);
+            break;
+          case JSOP_STRICTNE: // Fall through.
+          case JSOP_NE:
+            *result = (comp != 0);
+            break;
+          default:
+            JS_NOT_REACHED("Unexpected op.");
+            return false;
+        }
+
+        return true;
+    }
+
     if (!lhs.isNumber() || !rhs.isNumber())
         return false;