[CS] Don't create new locator when simplifying to anchor

We can directly use the version of `simplifyLocator` that works on
an anchor and path array ref instead.

Author: hamishknight

lib/Sema/CSDiag.cpp

@@ -820,7 +820,7 @@ bool FailureDiagnosis::diagnoseGeneralOverloadFailure(Constraint *constraint) {
   // Get the referenced expression from the failed constraint.
   auto anchor = expr;
   if (auto locator = bindOverload->getLocator()) {
-    anchor = simplifyLocatorToAnchor(CS, locator);
+    anchor = simplifyLocatorToAnchor(locator);
     if (!anchor)
       return false;
   }
@@ -1002,7 +1002,7 @@ bool FailureDiagnosis::diagnoseGeneralConversionFailure(Constraint *constraint){
   bool resolvedAnchorToExpr = false;
 
   if (auto locator = constraint->getLocator()) {
-    anchor = simplifyLocatorToAnchor(CS, locator);
+    anchor = simplifyLocatorToAnchor(locator);
     if (anchor)
       resolvedAnchorToExpr = true;
     else
@@ -5390,7 +5390,7 @@ bool FailureDiagnosis::visitUnresolvedMemberExpr(UnresolvedMemberExpr *E) {
   Constraint *memberConstraint = nullptr;
   auto checkConstraint = [&](Constraint *C) {
     if (C->getKind() == ConstraintKind::UnresolvedValueMember &&
-        simplifyLocatorToAnchor(CS, C->getLocator()) == E)
+        simplifyLocatorToAnchor(C->getLocator()) == E)
       memberConstraint = C;
   };
 

lib/Sema/CSDiagnostics.cpp

@@ -212,7 +212,7 @@ FailureDiagnostic::getFunctionArgApplyInfo(ConstraintLocator *locator) const {
   auto *argLocator = cs.getConstraintLocator(
       anchor, argPath, ConstraintLocator::getSummaryFlagsForPath(argPath));
 
-  auto *argExpr = simplifyLocatorToAnchor(cs, argLocator);
+  auto *argExpr = simplifyLocatorToAnchor(argLocator);
 
   // If we were unable to simplify down to the argument expression, we don't
   // know what this is.

lib/Sema/CSSimplify.cpp

@@ -2161,7 +2161,7 @@ static ConstraintFix *fixPropertyWrapperFailure(
       baseExpr = SE->getBase();
     else if (auto *MRE = dyn_cast<MemberRefExpr>(anchor))
       baseExpr = MRE->getBase();
-    else if (auto *anchor = simplifyLocatorToAnchor(cs, locator))
+    else if (auto *anchor = simplifyLocatorToAnchor(locator))
       baseExpr = anchor;
   }
 
@@ -2300,9 +2300,7 @@ bool ConstraintSystem::repairFailures(
     // default values, let's see whether error is related to missing
     // explicit call.
     if (fnType->getNumParams() > 0) {
-      auto *anchor =
-          simplifyLocatorToAnchor(*this, getConstraintLocator(locator));
-
+      auto *anchor = simplifyLocatorToAnchor(getConstraintLocator(locator));
       if (!anchor)
         return false;
 

lib/Sema/ConstraintSystem.cpp

@@ -2625,7 +2625,7 @@ bool ConstraintSystem::diagnoseAmbiguity(Expr *expr,
 
     // If we can't resolve the locator to an anchor expression with no path,
     // we can't diagnose this well.
-    auto *anchor = simplifyLocatorToAnchor(*this, overload.locator);
+    auto *anchor = simplifyLocatorToAnchor(overload.locator);
     if (!anchor)
       continue;
     auto it = indexMap.find(anchor);
@@ -2666,7 +2666,7 @@ bool ConstraintSystem::diagnoseAmbiguity(Expr *expr,
   if (bestOverload) {
     auto &overload = diff.overloads[*bestOverload];
     auto name = getOverloadChoiceName(overload.choices);
-    auto anchor = simplifyLocatorToAnchor(*this, overload.locator);
+    auto anchor = simplifyLocatorToAnchor(overload.locator);
 
     // Emit the ambiguity diagnostic.
     auto &tc = getTypeChecker();
@@ -2718,17 +2718,21 @@ bool ConstraintSystem::diagnoseAmbiguity(Expr *expr,
   return false;
 }
 
-Expr *constraints::simplifyLocatorToAnchor(ConstraintSystem &cs,
-                                           ConstraintLocator *locator) {
-  if (!locator || !locator->getAnchor())
+Expr *constraints::simplifyLocatorToAnchor(ConstraintLocator *locator) {
+  if (!locator)
     return nullptr;
 
-  SourceRange range;
-  locator = simplifyLocator(cs, locator, range);
-  if (!locator->getAnchor() || !locator->getPath().empty())
+  auto *anchor = locator->getAnchor();
+  if (!anchor)
     return nullptr;
 
-  return locator->getAnchor();
+  SourceRange range;
+  auto path = locator->getPath();
+  simplifyLocator(anchor, path, range);
+
+  // We only want the new anchor if all the path elements have been simplified
+  // away.
+  return path.empty() ? anchor : nullptr;
 }
 
 Expr *constraints::getArgumentExpr(Expr *expr, unsigned index) {

lib/Sema/ConstraintSystem.h

@@ -3950,7 +3950,7 @@ void simplifyLocator(Expr *&anchor,
 ///
 /// \returns the anchor expression if it fully describes the locator, or
 /// null otherwise.
-Expr *simplifyLocatorToAnchor(ConstraintSystem &cs, ConstraintLocator *locator);
+Expr *simplifyLocatorToAnchor(ConstraintLocator *locator);
 
 /// Retrieve argument at specified index from given expression.
 /// The expression could be "application", "subscript" or "member" call.