RequirementMachine: Add -requirement-machine-generic-signatures flag

Just as with the others, this has three values: on, off, and verify.
Not hooked up for now.

Author: slavapestov

include/swift/Basic/LangOptions.h

@@ -473,11 +473,11 @@ namespace swift {
     /// Enables fine-grained debug output from the requirement machine.
     std::string DebugRequirementMachine;
 
-    /// Maximum iteration count for requirement machine confluent completion
+    /// Maximum iteration count for requirement machine Knuth-Bendix completion
     /// algorithm.
     unsigned RequirementMachineStepLimit = 4000;
 
-    /// Maximum term length for requirement machine confluent completion
+    /// Maximum term length for requirement machine Knuth-Bendix completion
     /// algorithm.
     unsigned RequirementMachineDepthLimit = 10;
 
@@ -486,6 +486,10 @@ namespace swift {
     RequirementMachineMode RequirementMachineProtocolSignatures =
         RequirementMachineMode::Disabled;
 
+    /// Enable the new experimental generic signature minimization algorithm.
+    RequirementMachineMode RequirementMachineGenericSignatures =
+        RequirementMachineMode::Disabled;
+
     /// Sets the target we are building for and updates platform conditions
     /// to match.
     ///

include/swift/Option/Options.td

@@ -624,6 +624,10 @@ def requirement_machine_protocol_signatures_EQ : Joined<["-"], "requirement-mach
   Flags<[FrontendOption]>,
   HelpText<"Control usage of experimental protocol requirement signature minimization: 'on', 'off', or 'verify'">;
 
+def requirement_machine_generic_signatures_EQ : Joined<["-"], "requirement-machine-generic-signatures=">,
+  Flags<[FrontendOption]>,
+  HelpText<"Control usage of experimental generic signature minimization: 'on', 'off', or 'verify'">;
+
 def experimental_hermetic_seal_at_link:
   Flag<["-"], "experimental-hermetic-seal-at-link">,
   Flags<[FrontendOption, HelpHidden]>,

lib/Frontend/CompilerInvocation.cpp

@@ -859,6 +859,20 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
                      A->getAsString(Args), A->getValue());
   }
 
+  if (auto A = Args.getLastArg(OPT_requirement_machine_generic_signatures_EQ)) {
+    auto value = llvm::StringSwitch<Optional<RequirementMachineMode>>(A->getValue())
+        .Case("off", RequirementMachineMode::Disabled)
+        .Case("on", RequirementMachineMode::Enabled)
+        .Case("verify", RequirementMachineMode::Verify)
+        .Default(None);
+
+    if (value)
+      Opts.RequirementMachineGenericSignatures = *value;
+    else
+      Diags.diagnose(SourceLoc(), diag::error_invalid_arg_value,
+                     A->getAsString(Args), A->getValue());
+  }
+
   Opts.DumpRequirementMachine = Args.hasArg(
       OPT_dump_requirement_machine);
   Opts.AnalyzeRequirementMachine = Args.hasArg(