SILCombine: make the value_to_bridge_object peephole less conservative.

We can always eliminate ARC operations on the result of a value_to_bridge_object instruction.
There is no need to restrict the operand to a specific SIL pattern.

Author: eeckstein

lib/SILOptimizer/SILCombiner/SILCombinerMiscVisitors.cpp

@@ -686,20 +686,6 @@ SILInstruction *SILCombiner::visitCondFailInst(CondFailInst *CFI) {
   return nullptr;
 }
 
-static bool isValueToBridgeObjectremovable(ValueToBridgeObjectInst *VTBOI) {
-  SILValue operand = VTBOI->getOperand();
-  // If operand is a struct $UInt (% : $Builtin.), fetch the real source
-  if (auto *SI = dyn_cast<StructInst>(operand)) {
-    assert(SI->SILInstruction::getAllOperands().size() == 1 &&
-           "Expected a single operand");
-    operand = SI->getOperand(0);
-  }
-  if (auto *BI = dyn_cast<BuiltinInst>(operand)) {
-    return (BI->getBuiltinInfo().ID == BuiltinValueKind::StringObjectOr);
-  }
-  return false;
-}
-
 SILInstruction *SILCombiner::visitStrongRetainInst(StrongRetainInst *SRI) {
   // Retain of ThinToThickFunction is a no-op.
   SILValue funcOper = SRI->getOperand();
@@ -718,8 +704,7 @@ SILInstruction *SILCombiner::visitStrongRetainInst(StrongRetainInst *SRI) {
   // builtin "stringObjectOr_Int64" (or to tag the string)
   // value_to_bridge_object (cast the UInt to bridge object)
   if (auto *VTBOI = dyn_cast<ValueToBridgeObjectInst>(SRI->getOperand())) {
-    if (isValueToBridgeObjectremovable(VTBOI))
-      return eraseInstFromFunction(*SRI);
+    return eraseInstFromFunction(*SRI);
   }
 
   // Sometimes in the stdlib due to hand offs, we will see code like:
@@ -1169,8 +1154,7 @@ SILInstruction *SILCombiner::visitStrongReleaseInst(StrongReleaseInst *SRI) {
   // builtin "stringObjectOr_Int64" (or to tag the string)
   // value_to_bridge_object (cast the UInt to bridge object)
   if (auto *VTBOI = dyn_cast<ValueToBridgeObjectInst>(SRI->getOperand())) {
-    if (isValueToBridgeObjectremovable(VTBOI))
-      return eraseInstFromFunction(*SRI);
+    return eraseInstFromFunction(*SRI);
   }
 
   // Release of a classbound existential converted from a class is just a

test/SILOptimizer/sil_combine.sil

@@ -3505,3 +3505,16 @@ bb0:
   %4 = apply %2() : $@noescape @callee_guaranteed () -> Builtin.Int32
   return %4 : $Builtin.Int32
 }
+
+// CHECK-LABEL: sil @optimize_arc_with_value_to_bridge_object
+// CHECK:      bb0(%0 : $Builtin.Int64):
+// CHECK-NEXT: struct $UInt64
+// CHECK-NEXT: value_to_bridge_object
+// CHECK-NEXT: return
+sil @optimize_arc_with_value_to_bridge_object : $@convention(thin) (Builtin.Int64) -> Builtin.BridgeObject {
+bb0(%0 : $Builtin.Int64):
+  %1 = struct $UInt64 (%0 : $Builtin.Int64)
+  %2 = value_to_bridge_object %1 : $UInt64
+  strong_retain %2 : $Builtin.BridgeObject
+  return %2 : $Builtin.BridgeObject
+}