[SILGen] Eliminate SILGen-specific handling of imported, synthesized conformances

Now that Sema communicates its "used" conformances to SILGen, there is
no reason for SILGen to separately look for "used" conformances. NFC

Author: DougGregor

lib/SILGen/SILGenExpr.cpp

@@ -1450,7 +1450,6 @@ ManagedValue SILGenFunction::getManagedValue(SILLocation loc,
 
 RValue RValueEmitter::visitForcedCheckedCastExpr(ForcedCheckedCastExpr *E,
                                                  SGFContext C) {
-  SGF.checkForImportedUsedConformances(E);
   return emitUnconditionalCheckedCast(SGF, E, E->getSubExpr(), E->getType(),
                                       E->getCastKind(), C);
 }
@@ -1459,14 +1458,12 @@ RValue RValueEmitter::visitForcedCheckedCastExpr(ForcedCheckedCastExpr *E,
 RValue RValueEmitter::
 visitConditionalCheckedCastExpr(ConditionalCheckedCastExpr *E,
                                 SGFContext C) {
-  SGF.checkForImportedUsedConformances(E);
   ManagedValue operand = SGF.emitRValueAsSingleValue(E->getSubExpr());
   return emitConditionalCheckedCast(SGF, E, operand, E->getSubExpr()->getType(),
                                     E->getType(), E->getCastKind(), C);
 }
 
 RValue RValueEmitter::visitIsExpr(IsExpr *E, SGFContext C) {
-  SGF.checkForImportedUsedConformances(E);
   SILValue isa = emitIsa(SGF, E, E->getSubExpr(),
                          E->getCastTypeLoc().getType(), E->getCastKind());
 
@@ -1480,7 +1477,6 @@ RValue RValueEmitter::visitIsExpr(IsExpr *E, SGFContext C) {
 }
 
 RValue RValueEmitter::visitCoerceExpr(CoerceExpr *E, SGFContext C) {
-  SGF.checkForImportedUsedConformances(E);
   return visit(E->getSubExpr(), C);
 }
 

lib/SILGen/SILGenFunction.cpp

@@ -39,7 +39,6 @@ SILGenFunction::SILGenFunction(SILGenModule &SGM, SILFunction &F)
     Cleanups(*this)
 {
   B.setCurrentDebugScope(F.getDebugScope());
-  checkForImportedUsedConformances(F.getLoweredType().getSwiftType());
 }
 
 /// SILGenFunction destructor - called after the entire function's AST has been
@@ -945,18 +944,3 @@ SILGenBuilder::createAllocExistentialBox(SILLocation Loc,
                                                ConcreteType,
                                                Conformances);
 }
-
-void SILGenFunction::checkForImportedUsedConformances(Type type) {
-  // Recognize _BridgedNSError, which must pull in its witness table for
-  // dynamic casts to work
-  if (auto bridgedNSErrorProtocol =
-          getASTContext().getProtocol(KnownProtocolKind::BridgedNSError)) {
-    if (auto nominalDecl = type->getAnyNominal()) {
-      SmallVector<ProtocolConformance *, 4> conformances;
-      if (nominalDecl->lookupConformance(
-              SGM.SwiftModule, bridgedNSErrorProtocol, conformances)) {
-        SGM.useConformance(ProtocolConformanceRef(conformances.front()));
-      }
-    }
-  }
-}

lib/SILGen/SILGenFunction.h

@@ -1593,16 +1593,6 @@ class LLVM_LIBRARY_VISIBILITY SILGenFunction
   /// Produce a substitution for invoking a pointer argument conversion
   /// intrinsic.
   Substitution getPointerSubstitution(Type pointerType);
-
-  /// Recognize used conformances from an imported type when we must emit the
-  /// witness table.
-  ///
-  /// This arises in _BridgedNSError, where we wouldn't otherwise pull in the
-  /// witness table, causing dynamic casts to perform incorrectly.
-  void checkForImportedUsedConformances(Type type);
-  void checkForImportedUsedConformances(ExplicitCastExpr *expr) {
-    checkForImportedUsedConformances(expr->getCastTypeLoc().getType());
-  }
 };
 
 

lib/SILGen/SILGenPattern.cpp

@@ -1590,8 +1590,6 @@ void PatternMatchEmission::emitIsDispatch(ArrayRef<RowToSpecialize> rows,
   CanType sourceType = rows[0].Pattern->getType()->getCanonicalType();
   CanType targetType = getTargetType(rows[0]);
 
-  SGF.checkForImportedUsedConformances(targetType);
-
   // Make any abstraction modifications necessary for casting.
   SmallVector<ConsumableManagedValue, 4> borrowedValues;
   ConsumableManagedValue operand =