[ownership] Teach diagnose-unreachable to eliminate end_borrow from guaranteed block args when replacing the use of the block arg with a SILFunctionArgument.

A guaranteed function argument never is paired with an end_borrow, so when we
perform this sort of simplification, we need to eliminate the end_borrow of the
block argument.

Author: gottesmm

lib/SILOptimizer/Mandatory/DiagnoseUnreachable.cpp

@@ -91,6 +91,18 @@ class UnreachableUserCodeReportingState {
   llvm::DenseMap<const SILBasicBlock*, UnreachableInfo> MetaMap;
 };
 
+static void deleteEndBorrows(SILValue v) {
+  SmallVector<SILInstruction *, 4> endBorrowList;
+  for (auto *use : v->getUses()) {
+    if (auto *ebi = dyn_cast<EndBorrowInst>(use->getUser())) {
+      endBorrowList.push_back(ebi);
+    }
+  }
+  while (!endBorrowList.empty()) {
+    endBorrowList.pop_back_val()->eraseFromParent();
+  }
+}
+
 /// Propagate/remove basic block input values when all predecessors
 /// supply the same arguments.
 static void propagateBasicBlockArgs(SILBasicBlock &BB) {
@@ -173,6 +185,13 @@ static void propagateBasicBlockArgs(SILBasicBlock &BB) {
     // this to CCP and trigger another round of copy propagation.
     SILArgument *Arg = *AI;
 
+    // If this argument is guaranteed and Args[Idx] is a SILFunctionArgument,
+    // delete the end_borrow.
+    if (Arg->getOwnershipKind() == ValueOwnershipKind::Guaranteed &&
+        isa<SILFunctionArgument>(Args[Idx])) {
+      deleteEndBorrows(Arg);
+    }
+
     // We were able to fold, so all users should use the new folded value.
     Arg->replaceAllUsesWith(Args[Idx]);
     NumBasicBlockArgsPropagated++;

test/SILOptimizer/diagnose_unreachable.sil

@@ -3,6 +3,8 @@
 import Builtin
 import Swift
 
+sil @guaranteed_nativeobject_user : $@convention(thin) (@guaranteed Builtin.NativeObject) -> ()
+
 sil private @test1 : $() -> () {
 bb0:
   %5 = integer_literal $Builtin.Int1, 1
@@ -502,3 +504,21 @@ bb3:
   %9999 = tuple()
   return %9999 : $()
 }
+
+// CHECK-LABEL: sil [ossa] @eliminate_end_borrow_when_propagating_bb_args : $@convention(thin) (@guaranteed Builtin.NativeObject) -> () {
+// CHECK-NOT: end_borrow
+// CHECK: [[FUNC_REF:%.*]] = function_ref @guaranteed_nativeobject_user
+// CHECK-NEXT: apply [[FUNC_REF]](%0) :
+// CHECK-NOT: end_borrow
+// CHECK: } // end sil function 'eliminate_end_borrow_when_propagating_bb_args'
+sil [ossa] @eliminate_end_borrow_when_propagating_bb_args : $@convention(thin) (@guaranteed Builtin.NativeObject) -> () {
+bb0(%0 : @guaranteed $Builtin.NativeObject):
+  br bb1(%0 : $Builtin.NativeObject)
+
+bb1(%1 : @guaranteed $Builtin.NativeObject):
+  %2 = function_ref @guaranteed_nativeobject_user : $@convention(thin) (@guaranteed Builtin.NativeObject) -> ()
+  apply %2(%1) : $@convention(thin) (@guaranteed Builtin.NativeObject) -> ()
+  end_borrow %1 : $Builtin.NativeObject
+  %9999 = tuple()
+  return %9999 : $()
+}