[Torque] Add source positions for Torque files

To improve the Torque debugging experience, we can add source positions
for each line. This information is carried through the generated
CSA code (in <output directory>/gen/torque-generated/*.cc) and
embedded as SourcePositions in the Code object.

At snapshot time, these SourcePositions are stripped from the Code
object and turned into platform-appropriate line number debug
information.

At this time on Linux, you'll need to build with "is_clang=false"
in order to use GCC, because crucial steps are missing in Clang's
ability to convey the information into the binary successfully.

This CL also introduces a flag to control the existing source
information in CSA code. --enable-source-at-csa-bind is now set
to false by default because it's a bit confusing to "hop" between
source lines in .TQ files and in .CC files. I expect to continue
making adjustments there, as I want to provide helpful
debugging aids at the CSA level as well as the Torque level.
The current configuration prioritizes Torque.

A detailed guide on usage to follow (also on v8.dev).

Bug: v8:8418
Change-Id: Ib4226877ce4cae451bb4d0c546927e89f4e66b58
Reviewed-on: https://chromium-review.googlesource.com/c/1475473
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59636}

src/compiler/code-assembler.cc

@@ -1762,7 +1762,9 @@ void CodeAssemblerLabel::Bind(AssemblerDebugInfo debug_info) {
         << "\n#    previous: " << *label_->block();
     FATAL("%s", str.str().c_str());
   }
-  state_->raw_assembler_->SetSourcePosition(debug_info.file, debug_info.line);
+  if (FLAG_enable_source_at_csa_bind) {
+    state_->raw_assembler_->SetSourcePosition(debug_info.file, debug_info.line);
+  }
   state_->raw_assembler_->Bind(label_, debug_info);
   UpdateVariablesAfterBind();
 }

src/flag-definitions.h

@@ -850,6 +850,10 @@ DEFINE_STRING(mcpu, "auto", "enable optimization for specific cpu")
 DEFINE_BOOL(partial_constant_pool, true,
             "enable use of partial constant pools (X64 only)")
 
+// Controlling source positions for Torque/CSA code.
+DEFINE_BOOL(enable_source_at_csa_bind, false,
+            "Include source information in the binary at CSA bind locations.")
+
 // Deprecated ARM flags (replaced by arm_arch).
 DEFINE_MAYBE_BOOL(enable_armv7, "deprecated (use --arm_arch instead)")
 DEFINE_MAYBE_BOOL(enable_vfp3, "deprecated (use --arm_arch instead)")

src/torque/csa-generator.cc

@@ -54,8 +54,20 @@ Stack<std::string> CSAGenerator::EmitBlock(const Block* block) {
   return stack;
 }
 
+void CSAGenerator::EmitSourcePosition(SourcePosition pos, bool always_emit) {
+  const std::string& file = SourceFileMap::GetSource(pos.source);
+  if (always_emit || !previous_position_.CompareIgnoreColumn(pos)) {
+    // Lines in Torque SourcePositions are zero-based, while the
+    // CodeStubAssembler and downwind systems are one-based.
+    out_ << "    ca_.SetSourcePosition(\"" << file << "\", " << (pos.line + 1)
+         << ");\n";
+    previous_position_ = pos;
+  }
+}
+
 void CSAGenerator::EmitInstruction(const Instruction& instruction,
                                    Stack<std::string>* stack) {
+  EmitSourcePosition(instruction->pos);
   switch (instruction.kind()) {
 #define ENUM_ITEM(T)          \
   case InstructionKind::k##T: \

src/torque/csa-generator.h

@@ -18,7 +18,10 @@ class CSAGenerator {
  public:
   CSAGenerator(const ControlFlowGraph& cfg, std::ostream& out,
                base::Optional<Builtin::Kind> linkage = base::nullopt)
-      : cfg_(cfg), out_(out), linkage_(linkage) {}
+      : cfg_(cfg),
+        out_(out),
+        linkage_(linkage),
+        previous_position_(SourcePosition::Invalid()) {}
   base::Optional<Stack<std::string>> EmitGraph(Stack<std::string> parameters);
 
   static constexpr const char* ARGUMENTS_VARIABLE_STRING = "arguments";
@@ -31,6 +34,9 @@ class CSAGenerator {
   std::ostream& out_;
   size_t fresh_id_ = 0;
   base::Optional<Builtin::Kind> linkage_;
+  SourcePosition previous_position_;
+
+  void EmitSourcePosition(SourcePosition pos, bool always_emit = false);
 
   std::string PreCallableExceptionPreparation(
       base::Optional<Block*> catch_block);

src/torque/source-positions.h

@@ -14,6 +14,10 @@ namespace internal {
 namespace torque {
 
 class SourceId {
+ public:
+  static SourceId Invalid() { return SourceId(-1); }
+  int operator==(const SourceId& s) const { return id_ == s.id_; }
+
  private:
   explicit SourceId(int id) : id_(id) {}
   int id_;
@@ -24,6 +28,17 @@ struct SourcePosition {
   SourceId source;
   int line;
   int column;
+  static SourcePosition Invalid() {
+    SourcePosition pos{SourceId::Invalid(), -1, -1};
+    return pos;
+  }
+  int operator==(const SourcePosition& pos) const {
+    return line == pos.line && column == pos.column && source == pos.source;
+  }
+  int operator!=(const SourcePosition& pos) const { return !(*this == pos); }
+  bool CompareIgnoreColumn(const SourcePosition& pos) const {
+    return line == pos.line && source == pos.source;
+  }
 };
 
 DECLARE_CONTEXTUAL_VARIABLE(CurrentSourceFile, SourceId);