Disable a silcombine pattern that creates unoptimizable copies

The SILCombine of ref_to_raw_pointer uses ossa rauw which creates a copy.
The copy created cannot be removed because it has an escaping ownership.
Disabling the silcombine for ossa here to avoid generating unoptimizable copies.

Author: meg-gupta

lib/SILOptimizer/SILCombiner/SILCombinerCastVisitors.cpp

@@ -800,37 +800,13 @@ SILCombiner::visitRawPointerToRefInst(RawPointerToRefInst *rawToRef) {
   //   ->
   // (unchecked_ref_cast x X->Z)
   if (auto *refToRaw = dyn_cast<RefToRawPointerInst>(rawToRef->getOperand())) {
+    // We do this optimization only in non-ossa.
+    // In ossa, the copy created by ossa rauw is unoptimizable, skipping for
+    // this reason.
     if (!hasOwnership()) {
       return Builder.createUncheckedRefCast(
           rawToRef->getLoc(), refToRaw->getOperand(), rawToRef->getType());
     }
-
-    // raw_pointer_to_ref produces an unowned value. So we need to handle it
-    // especially with ownership.
-    {
-      SILValue originalRef = refToRaw->getOperand();
-      OwnershipRAUWHelper helper(ownershipFixupContext, rawToRef, originalRef);
-      if (helper) {
-        // Since we are using std::next, we use getAutogeneratedLocation to
-        // avoid any issues if our next insertion point is a terminator.
-        auto loc = RegularLocation::getAutoGeneratedLocation();
-        auto replacement = helper.prepareReplacement();
-        auto *newInst = Builder.createUncheckedRefCast(
-            loc, replacement, rawToRef->getType());
-        // If we have an operand with ownership, we need to change our
-        // unchecked_ref_cast to produce an unowned value. This is because
-        // otherwise, our unchecked_ref_cast will consume the underlying owned
-        // value, changing a BitwiseEscape to a LifetimeEnding use?! In
-        // contrast, for guaranteed, we are replacing a BitwiseEscape use
-        // (ref_to_rawpointer) with a ForwardedBorrowingUse (unchecked_ref_cast)
-        // which is safe.
-        if (newInst->getForwardingOwnershipKind() == OwnershipKind::Owned) {
-          newInst->setForwardingOwnershipKind(OwnershipKind::Unowned);
-        }
-        helper.perform(newInst);
-        return nullptr;
-      }
-    }
   }
 
   return nullptr;

test/SILOptimizer/sil_combine_ossa.sil

@@ -1572,11 +1572,8 @@ bb0(%0 : @owned $B):
 
 // CHECK-LABEL: sil [ossa] @unchecked_ref_cast_formation_owned : $@convention(thin) (@owned B) -> @owned F {
 // CHECK: bb0([[INPUT_REF:%[0-9]+]] : @owned $B):
-// CHECK-NOT: ref_to_raw_pointer
-// CHECK-NOT: raw_pointer_to_ref
-// CHECK: unchecked_ref_cast
-// CHECK-NOT: ref_to_raw_pointer
-// CHECK-NOT: raw_pointer_to_ref
+// CHECK: ref_to_raw_pointer
+// CHECK: raw_pointer_to_ref
 // CHECK: } // end sil function 'unchecked_ref_cast_formation_owned'
 sil [ossa] @unchecked_ref_cast_formation_owned : $@convention(thin) (@owned B) -> @owned F {
 bb0(%0 : @owned $B):
@@ -1589,11 +1586,8 @@ bb0(%0 : @owned $B):
 
 // CHECK-LABEL: sil [ossa] @unchecked_ref_cast_formation_guaranteed : $@convention(thin) (@guaranteed B) -> @owned F {
 // CHECK: bb0([[INPUT_REF:%[0-9]+]] : @guaranteed $B):
-// CHECK-NOT: ref_to_raw_pointer
-// CHECK-NOT: raw_pointer_to_ref
-// CHECK: unchecked_ref_cast
-// CHECK-NOT: ref_to_raw_pointer
-// CHECK-NOT: raw_pointer_to_ref
+// CHECK: ref_to_raw_pointer
+// CHECK: raw_pointer_to_ref
 // CHECK: } // end sil function 'unchecked_ref_cast_formation_guaranteed'
 sil [ossa] @unchecked_ref_cast_formation_guaranteed : $@convention(thin) (@guaranteed B) -> @owned F {
 bb0(%0 : @guaranteed $B):
@@ -1605,11 +1599,8 @@ bb0(%0 : @guaranteed $B):
 
 // CHECK-LABEL: sil [ossa] @unchecked_ref_cast_formation_unowned : $@convention(thin) (B) -> F {
 // CHECK: bb0([[INPUT_REF:%[0-9]+]] :
-// CHECK-NOT: ref_to_raw_pointer
-// CHECK-NOT: raw_pointer_to_ref
-// CHECK: unchecked_ref_cast
-// CHECK-NOT: ref_to_raw_pointer
-// CHECK-NOT: raw_pointer_to_ref
+// CHECK: ref_to_raw_pointer
+// CHECK: raw_pointer_to_ref
 // CHECK: } // end sil function 'unchecked_ref_cast_formation_unowned'
 sil [ossa] @unchecked_ref_cast_formation_unowned : $@convention(thin) (B) -> F {
 bb0(%0 : @unowned $B):