[csa] add utilities for printf-style debugging

Adds CSA::Print(const char* s), which generates a runtime call to
Runtime::kGlobalPrint with a line-terminated ASCII string constant,
and CSA::DebugPrint(const char* prefix, Node* tagged_value), which
emits a runtime call to Runtime::kDebugPrint() with the tagged
value, optionally prefixed by an ascii string constant.

These simplify debugging TF builtins by providing a tool to easily
observe the contents of values at arbitrary points in a program,
without stepping endlessly through assembly in a debugger, and to
easily observe the path taken through a TF builtin.

These methods do not generate code in release builds.

BUG=v8:5268
R=ishell@chromium.org, danno@chromium.org, bmeurer@chromium.org

Review-Url: https://codereview.chromium.org/2651673003
Cr-Commit-Position: refs/heads/master@{#42660}

src/code-stub-assembler.cc

@@ -8365,5 +8365,29 @@ Node* CodeStubAssembler::AllocatePromiseReactionJobInfo(
   return result;
 }
 
+void CodeStubAssembler::Print(const char* s) {
+#ifdef DEBUG
+  std::string formatted(s);
+  formatted += "\n";
+  Handle<String> string = isolate()->factory()->NewStringFromAsciiChecked(
+      formatted.c_str(), TENURED);
+  CallRuntime(Runtime::kGlobalPrint, NoContextConstant(), HeapConstant(string));
+#endif
+}
+
+void CodeStubAssembler::Print(const char* prefix, Node* tagged_value) {
+#ifdef DEBUG
+  if (prefix != nullptr) {
+    std::string formatted(prefix);
+    formatted += ": ";
+    Handle<String> string = isolate()->factory()->NewStringFromAsciiChecked(
+        formatted.c_str(), TENURED);
+    CallRuntime(Runtime::kGlobalPrint, NoContextConstant(),
+                HeapConstant(string));
+  }
+  CallRuntime(Runtime::kGlobalPrint, NoContextConstant(), tagged_value);
+#endif
+}
+
 }  // namespace internal
 }  // namespace v8

src/code-stub-assembler.h

@@ -1167,6 +1167,11 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
                                        Node* deferred_on_resolve,
                                        Node* deferred_on_reject, Node* context);
 
+  // Support for printf-style debugging
+  void Print(const char* s);
+  void Print(const char* prefix, Node* tagged_value);
+  inline void Print(Node* tagged_value) { return Print(nullptr, tagged_value); }
+
  protected:
   void DescriptorLookupLinear(Node* unique_name, Node* descriptors, Node* nof,
                               Label* if_found, Variable* var_name_index,