Merge pull request swiftlang#18522 from rudkx/disable-perf-hacks

[ConstraintSystem] Add an option to disable the constraint solver per…

Author: rudkx

include/swift/Basic/LangOptions.h

@@ -122,6 +122,9 @@ namespace swift {
     /// completions.
     bool CodeCompleteCallPatternHeuristics = false;
 
+    /// Disable constraint system performance hacks.
+    bool DisableConstraintSolverPerformanceHacks = false;
+
     ///
     /// Flags for use by tests
     ///

include/swift/Option/FrontendOptions.td

@@ -183,6 +183,9 @@ def debug_time_function_bodies : Flag<["-"], "debug-time-function-bodies">,
 def debug_time_expression_type_checking : Flag<["-"], "debug-time-expression-type-checking">,
   HelpText<"Dumps the time it takes to type-check each expression">;
 
+def disable_constraint_solver_performance_hacks : Flag<["-"], "disable-constraint-solver-performance-hacks">,
+  HelpText<"Disable all the hacks in the constraint solver">;
+
 def debug_assert_immediately : Flag<["-"], "debug-assert-immediately">,
   DebugCrashOpt, HelpText<"Force an assertion failure immediately">;
 def debug_assert_after_parse : Flag<["-"], "debug-assert-after-parse">,

lib/Frontend/CompilerInvocation.cpp

@@ -352,6 +352,9 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.UseDarwinPreStableABIBit = true;
 #endif
 
+  Opts.DisableConstraintSolverPerformanceHacks |=
+      Args.hasArg(OPT_disable_constraint_solver_performance_hacks);
+
   // Must be processed after any other language options that could affect
   // platform conditions.
   bool UnsupportedOS, UnsupportedArch;

lib/Sema/CSGen.cpp

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information
@@ -3539,6 +3539,8 @@ Type ConstraintSystem::generateConstraints(Pattern *pattern,
 }
 
 void ConstraintSystem::optimizeConstraints(Expr *e) {
+  if (TC.getLangOpts().DisableConstraintSolverPerformanceHacks)
+    return;
 
   SmallVector<Expr *, 16> linkedExprs;
 

lib/Sema/CSRanking.cpp

@@ -86,6 +86,9 @@ void ConstraintSystem::increaseScore(ScoreKind kind, unsigned value) {
 }
 
 bool ConstraintSystem::worseThanBestSolution() const {
+  if (TC.getLangOpts().DisableConstraintSolverPerformanceHacks)
+    return false;
+
   if (retainAllSolutions())
     return false;
 

lib/Sema/CSSolver.cpp

@@ -129,8 +129,12 @@ Solution ConstraintSystem::finalize(
 
   // Update the best score we've seen so far.
   if (solverState && !retainAllSolutions()) {
-    assert(!solverState->BestScore || CurrentScore <= *solverState->BestScore);
-    solverState->BestScore = CurrentScore;
+    assert(TC.getLangOpts().DisableConstraintSolverPerformanceHacks ||
+           !solverState->BestScore || CurrentScore <= *solverState->BestScore);
+
+    if (!solverState->BestScore || CurrentScore <= *solverState->BestScore) {
+      solverState->BestScore = CurrentScore;
+    }
   }
 
   for (auto tv : TypeVariables) {
@@ -1763,6 +1767,9 @@ static bool shortCircuitDisjunctionAt(Constraint *constraint,
                                       Constraint *successfulConstraint,
                                       ASTContext &ctx) {
 
+  if (ctx.LangOpts.DisableConstraintSolverPerformanceHacks)
+    return false;
+
   // If the successfully applied constraint is favored, we'll consider that to
   // be the "best".
   if (successfulConstraint->isFavored() && !constraint->isFavored()) {
@@ -1832,6 +1839,9 @@ static bool shouldSkipDisjunctionChoice(ConstraintSystem &cs,
   if (!cs.shouldAttemptFixes() && choice.isUnavailable())
     return true;
 
+  if (cs.TC.getLangOpts().DisableConstraintSolverPerformanceHacks)
+    return false;
+
   // Don't attempt to solve for generic operators if we already have
   // a non-generic solution.