[turbofan] Make CheckString deopt reason more informative

Bug: v8:7310
Change-Id: I54f16a65d478d65cb7df611626397376df22a975
Reviewed-on: https://chromium-review.googlesource.com/928702Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51442}

src/compiler/effect-control-linearizer.cc

@@ -1492,8 +1492,8 @@ Node* EffectControlLinearizer::LowerCheckString(Node* node, Node* frame_state) {
 
   Node* check = __ Uint32LessThan(value_instance_type,
                                   __ Uint32Constant(FIRST_NONSTRING_TYPE));
-  __ DeoptimizeIfNot(DeoptimizeReason::kWrongInstanceType, params.feedback(),
-                     check, frame_state);
+  __ DeoptimizeIfNot(DeoptimizeReason::kNotAString, params.feedback(), check,
+                     frame_state);
   return value;
 }
 

src/deoptimize-reason.h

@@ -41,6 +41,7 @@ namespace internal {
   V(NotAJavaScriptObject, "not a JavaScript object")                           \
   V(NotANumberOrOddball, "not a Number or Oddball")                            \
   V(NotASmi, "not a Smi")                                                      \
+  V(NotAString, "not a String")                                                \
   V(NotASymbol, "not a Symbol")                                                \
   V(OutOfBounds, "out of bounds")                                              \
   V(Overflow, "overflow")                                                      \