Merge pull request #36369 from eeckstein/dead-cast-elimination

SILCombine: remove dead unconditional_checked_cast

Author: eeckstein

lib/SILOptimizer/Analysis/SimplifyInstruction.cpp

@@ -322,17 +322,6 @@ SILValue InstSimplifier::visitRefToRawPointerInst(RefToRawPointerInst *RefToRaw)
   return SILValue();
 }
 
-SILValue
-InstSimplifier::
-visitUnconditionalCheckedCastInst(UnconditionalCheckedCastInst *UCCI) {
-  // (UCCI downcast (upcast x #type1 to #type2) #type2 to #type1) -> x
-  if (auto *upcast = dyn_cast<UpcastInst>(UCCI->getOperand()))
-    if (UCCI->getType() == upcast->getOperand()->getType())
-      return upcast->getOperand();
-
-  return SILValue();
-}
-
 /// If the only use of a cast is a destroy, just destroy the cast operand.
 static SILValue simplifyDeadCast(SingleValueInstruction *Cast) {
   if (!Cast->hasUsesOfAnyResult())
@@ -356,6 +345,17 @@ static SILValue simplifyDeadCast(SingleValueInstruction *Cast) {
   return Cast->getOperand(0);
 }
 
+SILValue
+InstSimplifier::
+visitUnconditionalCheckedCastInst(UnconditionalCheckedCastInst *UCCI) {
+  // (UCCI downcast (upcast x #type1 to #type2) #type2 to #type1) -> x
+  if (auto *upcast = dyn_cast<UpcastInst>(UCCI->getOperand()))
+    if (UCCI->getType() == upcast->getOperand()->getType())
+      return upcast->getOperand();
+
+  return simplifyDeadCast(UCCI);
+}
+
 SILValue
 InstSimplifier::
 visitUncheckedRefCastInst(UncheckedRefCastInst *OPRI) {

test/SILOptimizer/sil_combine.sil

@@ -554,6 +554,23 @@ bb0(%0 : $HeapBufferStorage<T_0_0, T_0_1>):
   return %3 : $HeapBufferStorage<T_0_0, T_0_1>
 }
 
+class Derived : C {}
+
+// CHECK-LABEL: sil @dead_unconditional_checked_cast :
+// CHECK-NOT:   unconditional_checked_cast
+// CHECK:     bb1:
+// CHECK:       strong_release %0
+// CHECK:     } // end sil function 'dead_unconditional_checked_cast'
+sil @dead_unconditional_checked_cast : $@convention(thin) (@owned C) -> () {
+bb0(%0 : $C):
+  %1 = unconditional_checked_cast %0 : $C to Derived
+  br bb1
+bb1:
+  strong_release %1 : $Derived
+  %r = tuple ()
+  return %r : $()
+}
+
 // CHECK-LABEL: sil @cond_fail_applied_to_zero_removal
 // CHECK: bb0
 // CHECK-NEXT: cond_fail

test/SILOptimizer/sil_combine_ossa.sil

@@ -548,6 +548,20 @@ bb0(%0 : @owned $HeapBufferStorage<T_0_0, T_0_1>):
   return %3 : $HeapBufferStorage<T_0_0, T_0_1>
 }
 
+class Derived : C {}
+
+// CHECK-LABEL: sil [ossa] @dead_unconditional_checked_cast :
+// CHECK-NOT: unconditional_checked_cast
+// CHECK:     destroy_value %0
+// CHECK: } // end sil function 'dead_unconditional_checked_cast'
+sil [ossa] @dead_unconditional_checked_cast : $@convention(thin) (@owned C) -> () {
+bb0(%0 : @owned $C):
+  %1 = unconditional_checked_cast %0 : $C to Derived
+  destroy_value %1 : $Derived
+  %r = tuple ()
+  return %r : $()
+}
+
 // CHECK-LABEL: sil [ossa] @cond_fail_applied_to_zero_removal :
 // CHECK: bb0
 // CHECK-NEXT: cond_fail