[Request-evaluator] Add GraphViz output option -output-request-graphviz.

Introduce a command-line option to visualize the complete set of output
request dependencies evaluated by a particular compile action. This is
exposing existing visualization facilities to the (-frontend) command line.

Author: DougGregor

include/swift/Frontend/FrontendOptions.h

@@ -70,6 +70,10 @@ class FrontendOptions {
   /// The path to which we should store indexing data, if any.
   std::string IndexStorePath;
 
+  /// The path to which we should emit GraphViz output for the complete
+  /// request-evaluator graph.
+  std::string RequestEvaluatorGraphVizPath;
+
   /// Emit index data for imported serialized swift system modules.
   bool IndexSystemModules = false;
 

include/swift/Option/FrontendOptions.td

@@ -169,6 +169,8 @@ def debug_forbid_typecheck_prefix : Separate<["-"], "debug-forbid-typecheck-pref
 
 def debug_cycles : Flag<["-"], "debug-cycles">,
   HelpText<"Print out debug dumps when cycles are detected in evaluation">;
+def output_request_graphviz : Separate<["-"], "output-request-graphviz">,
+  HelpText<"Emit GraphViz output visualizing the request graph">;
 
 def debug_time_compilation : Flag<["-"], "debug-time-compilation">,
   HelpText<"Prints the time taken by each compilation phase">;

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -60,6 +60,10 @@ bool ArgsToFrontendOptionsConverter::convert(
   if (const Arg *A = Args.getLastArg(OPT_index_store_path)) {
     Opts.IndexStorePath = A->getValue();
   }
+  if (const Arg *A = Args.getLastArg(OPT_output_request_graphviz)) {
+    Opts.RequestEvaluatorGraphVizPath = A->getValue();
+  }
+
   Opts.IndexSystemModules |= Args.hasArg(OPT_index_system_modules);
 
   Opts.EmitVerboseSIL |= Args.hasArg(OPT_emit_verbose_sil);

lib/FrontendTool/FrontendTool.cpp

@@ -855,6 +855,13 @@ emitIndexData(CompilerInvocation &Invocation, CompilerInstance &Instance) {
   return hadEmitIndexDataError;
 }
 
+/// Emits the request-evaluator graph to the given file in GraphViz format.
+void emitRequestEvaluatorGraphViz(ASTContext &ctx, StringRef graphVizPath) {
+  std::error_code error;
+  llvm::raw_fd_ostream out(graphVizPath, error, llvm::sys::fs::F_Text);
+  ctx.evaluator.printDependenciesGraphviz(out);
+}
+
 static bool performCompileStepsPostSILGen(
     CompilerInstance &Instance, CompilerInvocation &Invocation,
     std::unique_ptr<SILModule> SM, bool astGuaranteedToCorrespondToSIL,
@@ -894,6 +901,17 @@ static bool performCompile(CompilerInstance &Instance,
   else
     Instance.performSema();
 
+  SWIFT_DEFER {
+    // Emit request-evaluator graph via GraphViz, if requested.
+    if (!Invocation.getFrontendOptions().RequestEvaluatorGraphVizPath.empty() &&
+        Instance.hasASTContext()) {
+      ASTContext &ctx = Instance.getASTContext();
+      emitRequestEvaluatorGraphViz(
+        ctx,
+        Invocation.getFrontendOptions().RequestEvaluatorGraphVizPath);
+    }
+  };
+
   if (Action == FrontendOptions::ActionType::Parse)
     return Instance.getASTContext().hadError();
 

lib/Serialization/SerializedModuleLoader.cpp

@@ -702,4 +702,4 @@ SerializedASTFile::getDiscriminatorForPrivateValue(const ValueDecl *D) const {
   Identifier discriminator = File.getDiscriminatorForPrivateValue(D);
   assert(!discriminator.empty() && "no discriminator found for value");
   return discriminator;
-}
+}

test/decl/class/circular_inheritance.swift

@@ -1,6 +1,7 @@
 // RUN: %target-typecheck-verify-swift
-// RUN: not %target-swift-frontend -typecheck -debug-cycles %s 2> %t.cycles
+// RUN: not %target-swift-frontend -typecheck -debug-cycles %s -output-request-graphviz %t.dot 2> %t.cycles
 // RUN: %FileCheck %s < %t.cycles
+// RUN: %FileCheck -check-prefix CHECK-DOT %s  < %t.dot
 
 class C : B { } // expected-error{{circular class inheritance 'C' -> 'B' -> 'A' -> 'C'}}
 class B : A { } // expected-note{{class 'B' declared here}}
@@ -46,3 +47,6 @@ class Outer3
 // CHECK-NEXT:          `--{{.*}}SuperclassTypeRequest
 // CHECK-NEXT:              `--{{.*}}InheritedTypeRequest(circular_inheritance.(file).Right@
 // CHECK-NEXT:                  `--{{.*}}SuperclassTypeRequest{{.*(cyclic dependency)}}
+
+// CHECK-DOT: digraph Dependencies
+// CHECK-DOT: label="InheritedTypeRequest