Improve casts analysis for bridged types.

Check if the outcome of a cast from an ObjC type to a Swift type or from a Swift type to an ObjC type can be statically determined.
This allows for folding of many such casts.

Swift SVN r26125

lib/SIL/DynamicCasts.cpp

@@ -242,6 +242,11 @@ swift::classifyDynamicCast(Module *M,
     source = sourceMetatype.getInstanceType();
     target = targetMetatype.getInstanceType();
 
+    if (source == target &&
+        targetMetatype.isAnyExistentialType() ==
+            sourceMetatype.isAnyExistentialType())
+      return DynamicCastFeasibility::WillSucceed;
+
     if (targetMetatype.isAnyExistentialType() && isa<ProtocolType>(target)) {
       auto Feasibility = classifyDynamicCastToProtocol(source,
                                                        target,
@@ -320,13 +325,34 @@ swift::classifyDynamicCast(Module *M,
   // FIXME: tuple conversions?
 
   // Check if there might be a bridging conversion.
-  if (source->isBridgeableObjectType()
-      && mayBridgeToObjectiveC(M, target)) {
+  if (source->isBridgeableObjectType() && mayBridgeToObjectiveC(M, target)) {
+    // Try to get the ObjC type which is bridged to target type.
+    assert(!target.isAnyExistentialType());
+    Optional<Type> ObjCTy = M->getASTContext().getBridgedToObjC(
+        M, /*inExpression*/ false, target, nullptr);
+    if (ObjCTy) {
+      // If the bridged ObjC type is known, check if
+      // source type can be casted into it.
+      return classifyDynamicCast(M, source,
+          ObjCTy.getValue().getCanonicalTypeOrNull(),
+          /* isSourceTypeExact */ false, isWholeModuleOpts);
+    }
     return DynamicCastFeasibility::MaySucceed;
   }
   
-  if (target->isBridgeableObjectType()
-      && mayBridgeToObjectiveC(M, source)) {
+  if (target->isBridgeableObjectType() && mayBridgeToObjectiveC(M, source)) {
+    // Try to get the ObjC type which is bridged to source type.
+    assert(!source.isAnyExistentialType());
+    Optional<Type> ObjCTy = M->getASTContext().getBridgedToObjC(
+        M, /*inExpression*/ false, source, nullptr);
+    if (ObjCTy) {
+      // If the bridged ObjC type is known, check if
+      // this type can be casted into target type.
+      return classifyDynamicCast(M,
+          ObjCTy.getValue().getCanonicalTypeOrNull(),
+          target,
+          /* isSourceTypeExact */ false, isWholeModuleOpts);
+    }
     return DynamicCastFeasibility::MaySucceed;
   }
 

test/SILPasses/cast_folding.swift

@@ -742,14 +742,72 @@ func callFooGeneric<T : PP>(c: T) -> Int {
 
 // Check that the inlined version of callFooGeneric contains only a trap
 // followed by unreachable and no code afterwards
-// CHECK-LABEL: sil @_TF12cast_folding16callForGenericCCFCS_2CCT_
+// CHECK-LABEL: sil [noinline] @_TF12cast_folding16callForGenericCCFCS_2CCT_
 // CHECK: builtin "int_trap"
 // CHECK-NEXT: unreachable
 // CHECK-NEXT: }
+@inline(never)
 public func callForGenericCC(c: CC) {
   callFoo(c)
 }
 
+// Check that compiler understands that this cast always succeeds
+// CHECK-LABEL: sil [noinline] @_TF12cast_folding30testBridgedCastFromObjCtoSwiftFCSo8NSStringSS
+// CHECK-NOT: cast
+// CHECK: function_ref @swift_bridgeNonVerbatimFromObjectiveC
+// CHECK: apply
+// CHECK: return
+@inline(never)
+public func testBridgedCastFromObjCtoSwift(ns: NSString) -> String {
+  return ns as String
+} 
+
+// Check that compiler understands that this cast always succeeds
+// CHECK-LABEL: sil [noinline] @_TF12cast_folding30testBridgedCastFromSwiftToObjCFSSCSo8NSString
+// CHECK-NOT: cast
+// CHECK: function_ref @_TFE10FoundationSS19_bridgeToObjectiveCfSSFT_CSo8NSString
+// CHECK: apply
+// CHECK: return
+@inline(never)
+public func testBridgedCastFromSwiftToObjC(s: String) -> NSString {
+  return s as NSString
+} 
+
+// Check that this cast does not get eliminated, because 
+// the compiler does not statically know if this object
+// is NSNumber can can be converted into Int.
+// CHECK-LABEL: sil [noinline] @_TF12cast_folding35testMayBeBridgedCastFromObjCtoSwiftFPSs9AnyObject_Si
+// CHECK: unconditional_checked_cast_addr
+// CHECK: return
+@inline(never)
+public func testMayBeBridgedCastFromObjCtoSwift(o: AnyObject) -> Int {
+  return o as! Int
+} 
+
+
+public func castObjCToSwift<T>(t: T) -> Int {
+  return t as! Int
+}
+
+// Check that compiler understands that this cast always fails
+// CHECK-LABEL: sil [noinline] @_TF12cast_folding37testFailingBridgedCastFromObjCtoSwiftFCSo8NSStringSi
+// CHECK: builtin "int_trap"
+// CHECK-NEXT: unreachable
+// CHECK-NEXT: }
+@inline(never)
+public func testFailingBridgedCastFromObjCtoSwift(ns: NSString) -> Int {
+  return castObjCToSwift(ns)
+} 
+
+// Check that compiler understands that this cast always fails
+// CHECK-LABEL: sil [noinline] @_TF12cast_folding37testFailingBridgedCastFromSwiftToObjCFSSSi
+// CHECK: builtin "int_trap"
+// CHECK-NEXT: unreachable
+// CHECK-NEXT: }
+@inline(never)
+public func testFailingBridgedCastFromSwiftToObjC(s: String) -> NSInteger {
+  return s as! NSInteger
+} 
 
 println("test0=\(test0())")