RequirementMachine: Add -enable-requirement-machine-loop-normalization flag

Author: slavapestov

include/swift/Basic/LangOptions.h

@@ -545,6 +545,10 @@ namespace swift {
     /// enabled. It can be disabled for debugging and testing.
     bool EnableRequirementMachineConcreteContraction = true;
 
+    /// Enable the stronger minimization algorithm. This is just for debugging;
+    /// if you have a testcase which requires this, please submit a bug report.
+    bool EnableRequirementMachineLoopNormalization = false;
+
     /// Enables dumping type witness systems from associated type inference.
     bool DumpTypeWitnessSystems = false;
 

include/swift/Option/FrontendOptions.td

@@ -359,6 +359,9 @@ def disable_requirement_machine_concrete_contraction : Flag<["-"], "disable-requ
   HelpText<"Disable preprocessing pass to eliminate conformance requirements "
            "on generic parameters which are made concrete">;
 
+def enable_requirement_machine_loop_normalization : Flag<["-"], "enable-requirement-machine-loop-normalization">,
+  HelpText<"Enable stronger minimization algorithm, for debugging only">;
+
 def dump_type_witness_systems : Flag<["-"], "dump-type-witness-systems">,
   HelpText<"Enables dumping type witness systems from associated type inference">;
 

lib/AST/RequirementMachine/HomotopyReduction.cpp

@@ -59,6 +59,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
+#include "RewriteContext.h"
 #include "RewriteSystem.h"
 
 using namespace swift;
@@ -627,6 +628,10 @@ void RewriteSystem::deleteRule(unsigned ruleID,
     if (!changed)
       continue;
 
+    if (Context.getASTContext().LangOpts.EnableRequirementMachineLoopNormalization) {
+      loop.computeNormalForm(*this);
+    }
+
     // The loop's path has changed, so we must invalidate the cached
     // result of findRulesAppearingOnceInEmptyContext().
     loop.markDirty();
@@ -723,6 +728,12 @@ void RewriteSystem::minimizeRewriteSystem() {
   propagateExplicitBits();
   processConflicts();
 
+  if (Context.getASTContext().LangOpts.EnableRequirementMachineLoopNormalization) {
+    for (auto &loop : Loops) {
+      loop.computeNormalForm(*this);
+    }
+  }
+
   // First pass:
   // - Eliminate all LHS-simplified non-conformance rules.
   // - Eliminate all RHS-simplified and substitution-simplified rules.

lib/Frontend/CompilerInvocation.cpp

@@ -1005,6 +1005,9 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   if (Args.hasArg(OPT_disable_requirement_machine_concrete_contraction))
     Opts.EnableRequirementMachineConcreteContraction = false;
 
+  if (Args.hasArg(OPT_enable_requirement_machine_loop_normalization))
+    Opts.EnableRequirementMachineLoopNormalization = true;
+
   Opts.DumpTypeWitnessSystems = Args.hasArg(OPT_dump_type_witness_systems);
 
   return HadError || UnsupportedOS || UnsupportedArch;