SIL: Update formal source type in SimplifyRefCasts when possible

We use the formal source type do decide whether a checked_cast_br is
known to succeed/fail. If we don't update it we loose that optimization

That is:

```
  checked_cast_br AnyObject in %2 : X to X, bb1, bb2
```

Will not be simplified even though the operand and the destintation type
matches.

Author: aschwaighofer

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyRefCasts.swift

@@ -69,6 +69,8 @@ private extension UnaryInstruction {
     let canEraseInst = singleUse?.instruction == self
     let replacement = inst.operands[0].value
 
+    let oldOperandType = operand.value.type
+
     if parentFunction.hasOwnership {
       if !canEraseInst && replacement.ownership == .owned {
         // We cannot add more uses to `replacement` without inserting a copy.
@@ -86,6 +88,15 @@ private extension UnaryInstruction {
       operand.set(to: replacement, context)
     }
 
+    if let ccb = self as? CheckedCastBranchInst {
+        // Make sure that loosing the formal source type is harmless (i.e the
+        // formal source type lowered equaled the operand SIL type before
+        // transformation).
+        let formalSrcType =  ccb.formalSrcType
+        if formalSrcType.loweredType(in: parentFunction, maximallyAbstracted: false) == oldOperandType {
+            ccb.updateSourceFormalTypeFromOperandLoweredType()
+        }
+    }
     if canEraseInst {
       context.erase(instructionIncludingDebugUses: inst)
     }

SwiftCompilerSources/Sources/SIL/Instruction.swift

@@ -1696,6 +1696,12 @@ final public class CheckedCastBranchInst : TermInst, UnaryInstruction {
   public var source: Value { operand.value }
   public var successBlock: BasicBlock { bridged.CheckedCastBranch_getSuccessBlock().block }
   public var failureBlock: BasicBlock { bridged.CheckedCastBranch_getFailureBlock().block }
+
+  public var formalSrcType : CanonicalType { CanonicalType(bridged: bridged.CheckedCastBranch_getFormalSrcType()) }
+
+  public func updateSourceFormalTypeFromOperandLoweredType() {
+    bridged.CheckedCastBranch_updateSourceFormalTypeFromOperandLoweredType()
+  }
 }
 
 final public class CheckedCastAddrBranchInst : TermInst {

include/swift/SIL/SILBridging.h

@@ -808,8 +808,10 @@ struct BridgedInstruction {
   BRIDGED_INLINE void LoadInst_setOwnership(SwiftInt ownership) const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedBasicBlock CheckedCastBranch_getSuccessBlock() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedBasicBlock CheckedCastBranch_getFailureBlock() const;
+  BRIDGED_INLINE BridgedCanType CheckedCastBranch_getFormalSrcType() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedBasicBlock CheckedCastAddrBranch_getSuccessBlock() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedBasicBlock CheckedCastAddrBranch_getFailureBlock() const;
+  BRIDGED_INLINE void CheckedCastBranch_updateSourceFormalTypeFromOperandLoweredType() const;
   BRIDGED_INLINE CastConsumptionKind CheckedCastAddrBranch_getConsumptionKind() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedSubstitutionMap ApplySite_getSubstitutionMap() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedCanType ApplySite_getSubstitutedCalleeType() const;

include/swift/SIL/SILBridgingImpl.h

@@ -1504,6 +1504,10 @@ void BridgedInstruction::LoadInst_setOwnership(SwiftInt ownership) const {
   getAs<swift::LoadInst>()->setOwnershipQualifier((swift::LoadOwnershipQualifier)ownership);
 }
 
+void BridgedInstruction::CheckedCastBranch_updateSourceFormalTypeFromOperandLoweredType() const {
+  getAs<swift::CheckedCastBranchInst>()->updateSourceFormalTypeFromOperandLoweredType();
+}
+
 BridgedBasicBlock BridgedInstruction::CheckedCastBranch_getSuccessBlock() const {
   return {getAs<swift::CheckedCastBranchInst>()->getSuccessBB()};
 }
@@ -1512,6 +1516,10 @@ BridgedBasicBlock BridgedInstruction::CheckedCastBranch_getFailureBlock() const
   return {getAs<swift::CheckedCastBranchInst>()->getFailureBB()};
 }
 
+BridgedCanType BridgedInstruction::CheckedCastBranch_getFormalSrcType() const {
+  return {getAs<swift::CheckedCastBranchInst>()->getSourceFormalType()};
+}
+
 BridgedBasicBlock BridgedInstruction::CheckedCastAddrBranch_getSuccessBlock() const {
   return {getAs<swift::CheckedCastAddrBranchInst>()->getSuccessBB()};
 }

include/swift/SIL/SILInstruction.h

@@ -11032,6 +11032,10 @@ class CheckedCastBranchInst final
   SILType getSourceLoweredType() const { return getOperand()->getType(); }
   CanType getSourceFormalType() const { return SrcFormalTy; }
 
+  void updateSourceFormalTypeFromOperandLoweredType() {
+    SrcFormalTy = getSourceLoweredType().getASTType();
+  }
+
   SILType getTargetLoweredType() const { return DestLoweredTy; }
   CanType getTargetFormalType() const { return DestFormalTy; }
 };

test/DebugInfo/simplify_checked_cast_br.sil

@@ -11,7 +11,7 @@ class X : B {}
 
 // CHECK-LABEL: sil [ossa] @test_ossa :
 // CHECK:         %0 = alloc_ref
-// CHECK-NEXT:  checked_cast_br AnyObject in %0 : $X
+// CHECK-NEXT:  checked_cast_br X in %0 : $X
 // CHECK:     bb2([[A:%.*]] : @owned $X):
 // CHECK-NEXT:  [[U:%.*]] = upcast [[A]] : $X to $B, loc "takethis":1:1
 // CHECK-NEXT:  [[E:%.*]] = init_existential_ref [[U]] {{.+}}, loc "takethis":1:1

test/SILOptimizer/devirt_covariant_return.swift

@@ -235,7 +235,7 @@ public class D2: D1 {
 // that D2.foo() is inlined thanks to this.
 // CHECK-LABEL: sil hidden [noinline] @$s23devirt_covariant_return7driver2ys5Int32VAA2D2CF
 // CHECK-NOT: class_method
-// CHECK: checked_cast_br [exact] D1 in
+// CHECK: checked_cast_br [exact] D2 in
 // CHECK: bb2
 // CHECK: global_addr
 // CHECK: load

test/SILOptimizer/simplify_checked_cast_br.sil

@@ -12,7 +12,7 @@ class X : B {}
 
 // CHECK-LABEL: sil @test_non_ossa :
 // CHECK:         %0 = alloc_ref
-// CHECK:         checked_cast_br AnyObject in %0 : $X
+// CHECK:         checked_cast_br X in %0 : $X
 // CHECK:       } // end sil function 'test_non_ossa'
 sil @test_non_ossa : $@convention(thin) () -> AnyObject {
 bb0:
@@ -31,7 +31,7 @@ bb2:
 
 // CHECK-LABEL: sil [ossa] @test_ossa :
 // CHECK:         %0 = alloc_ref
-// CHECK-O-NEXT:  checked_cast_br AnyObject in %0 : $X
+// CHECK-O-NEXT:  checked_cast_br X in %0 : $X
 // CHECK-ONONE:   checked_cast_br AnyObject in %2 : $AnyObject
 // CHECK-O:     bb2([[A:%.*]] : @owned $X):
 // CHECK-O-NEXT:  [[U:%.*]] = upcast [[A]] : $X to $B
@@ -75,7 +75,7 @@ bb2(%7 : @owned $B):
 
 // CHECK-LABEL: sil [ossa] @test_borrow :
 // CHECK:         %1 = begin_borrow
-// CHECK-NEXT:    checked_cast_br any P in %1 : $X
+// CHECK-NEXT:    checked_cast_br X in %1 : $X
 // CHECK:       bb2([[A:%.*]] : @guaranteed $X):
 // CHECK-NEXT:    [[U:%.*]] = upcast [[A]] : $X to $B
 // CHECK-NEXT:    [[E:%.*]] = init_existential_ref [[U]] : $B