[turbofan] Introduce a SpeculativeToNumber operator.

src/compiler/loop-variable-optimizer.cc

Index: src/compiler/loop-variable-optimizer.cc
diff --git a/src/compiler/loop-variable-optimizer.cc b/src/compiler/loop-variable-optimizer.cc
index b8c158300c801de580f94488e22d388f426e678d..d5c37860f65dcbc8f1ff56ce339150211832cc8e 100644
--- a/src/compiler/loop-variable-optimizer.cc
+++ b/src/compiler/loop-variable-optimizer.cc
@@ -317,7 +317,8 @@ InductionVariable* LoopVariableOptimizer::TryGetInductionVariable(Node* phi) {
 
   // TODO(jarin) Support both sides.
   if (arith->InputAt(0) != phi) {
-    if (arith->InputAt(0)->opcode() != IrOpcode::kJSToNumber ||
+    if ((arith->InputAt(0)->opcode() != IrOpcode::kJSToNumber &&
+         arith->InputAt(0)->opcode() != IrOpcode::kSpeculativeToNumber) ||
         arith->InputAt(0)->InputAt(0) != phi) {
       return nullptr;
     }