Bug 1318926 - constant-fold asm.js RSh expressions again. r=nbp

--HG--
extra : rebase_source : 7ac6438095eafb116ffeaf217d8dc07270bebf58

js/src/jit/MIR.cpp

@@ -3112,6 +3112,11 @@ MBinaryArithInstruction::constantDoubleResult(TempAllocator& alloc)
 MDefinition*
 MRsh::foldsTo(TempAllocator& alloc)
 {
+    MDefinition* f = MBinaryBitwiseInstruction::foldsTo(alloc);
+
+    if (f != this)
+        return f;
+
     MDefinition* lhs = getOperand(0);
     MDefinition* rhs = getOperand(1);