RequirementMachine: Add flags for completion depth and step limits

Author: slavapestov

include/swift/Basic/LangOptions.h

@@ -433,6 +433,14 @@ namespace swift {
     /// Enables debugging output from the requirement machine.
     bool DebugRequirementMachine = false;
 
+    /// Maximum iteration count for requirement machine confluent completion
+    /// algorithm.
+    unsigned RequirementMachineStepLimit = 1000;
+
+    /// Maximum term length for requirement machine confluent completion
+    /// algorithm.
+    unsigned RequirementMachineDepthLimit = 10;
+
     /// Sets the target we are building for and updates platform conditions
     /// to match.
     ///

include/swift/Option/FrontendOptions.td

@@ -283,6 +283,14 @@ def disable_requirement_machine : Flag<["-"], "disable-requirement-machine">,
 def debug_requirement_machine : Flag<["-"], "debug-requirement-machine">,
   HelpText<"Enables debugging output from the generics implementation">;
 
+def requirement_machine_step_limit : Separate<["-"], "requirement-machine-step-limit">,
+  Flags<[FrontendOption, HelpHidden, DoesNotAffectIncrementalBuild]>,
+  HelpText<"Set the maximum steps before we give up on confluent completion">;
+
+def requirement_machine_depth_limit : Separate<["-"], "requirement-machine-depth-limit">,
+  Flags<[FrontendOption, HelpHidden, DoesNotAffectIncrementalBuild]>,
+  HelpText<"Set the maximum depth before we give up on confluent completion">;
+
 def debug_generic_signatures : Flag<["-"], "debug-generic-signatures">,
   HelpText<"Debug generic signatures">;
 

lib/AST/RequirementMachine.cpp

@@ -205,8 +205,9 @@ void RequirementMachine::addGenericSignature(CanGenericSignature sig) {
   Impl->System.initialize(std::move(builder.Rules),
                           std::move(builder.Protocols));
 
-  // FIXME: Add command line flag
-  auto result = Impl->System.computeConfluentCompletion(1000, 10);
+  auto result = Impl->System.computeConfluentCompletion(
+      Context.LangOpts.RequirementMachineStepLimit,
+      Context.LangOpts.RequirementMachineDepthLimit);
 
   switch (result) {
   case RewriteSystem::CompletionResult::Success:

lib/Frontend/CompilerInvocation.cpp

@@ -798,6 +798,28 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.DebugRequirementMachine = Args.hasArg(
       OPT_debug_requirement_machine);
 
+  if (const Arg *A = Args.getLastArg(OPT_requirement_machine_step_limit)) {
+    unsigned limit;
+    if (StringRef(A->getValue()).getAsInteger(10, limit)) {
+      Diags.diagnose(SourceLoc(), diag::error_invalid_arg_value,
+                     A->getAsString(Args), A->getValue());
+      HadError = true;
+    } else {
+      Opts.RequirementMachineStepLimit = limit;
+    }
+  }
+
+  if (const Arg *A = Args.getLastArg(OPT_requirement_machine_depth_limit)) {
+    unsigned limit;
+    if (StringRef(A->getValue()).getAsInteger(10, limit)) {
+      Diags.diagnose(SourceLoc(), diag::error_invalid_arg_value,
+                     A->getAsString(Args), A->getValue());
+      HadError = true;
+    } else {
+      Opts.RequirementMachineDepthLimit = limit;
+    }
+  }
+
   return HadError || UnsupportedOS || UnsupportedArch;
 }