Remove old hack in transitive address use walker for store_borrow

Now that store_borrows are represented correctly, remove this hack.

Author: meg-gupta

lib/SIL/Utils/AddressWalker.cpp

@@ -25,16 +25,6 @@ AddressUseKind TransitiveAddressWalker::walk(SILValue projectedAddress) && {
   // When we exit, set the result to be invalidated so we can't use this again.
   SWIFT_DEFER { didInvalidate = true; };
 
-  // If the projectedAddress is dead, it is itself a leaf use. Since we don't
-  // have an operand for it, simply bail. Dead projectedAddress is unexpected.
-  //
-  // TODO: store_borrow is currently an InteriorPointer with no uses, so we end
-  // up bailing. It should be in a dependence scope instead. It's not clear why
-  // it produces an address at all.
-  if (projectedAddress->use_empty()) {
-    return AddressUseKind::PointerEscape;
-  }
-
   StackList<Operand *> worklist(projectedAddress->getFunction());
   SmallPtrSet<Operand *, 32> visitedOperands;
 

test/SILOptimizer/copy_propagation_borrow.sil

@@ -501,6 +501,7 @@ bb0:
   %copy1 = copy_value %borrow1 : $C
   %borrow2 = begin_borrow %copy1 : $C
   %addr = ref_element_addr %borrow2 : $C, #C.a
+  %ptr = address_to_pointer %addr : $*Int64 to $Builtin.RawPointer
   cond_br undef, bb1, bb2
 bb1:
   // inside use
@@ -1201,4 +1202,3 @@ bb0(%0 : @guaranteed $C):
   %7 = tuple ()
   return %7 : $()
 }
-

test/SILOptimizer/liveness_unit.sil

@@ -222,19 +222,13 @@ bb4(%phi : @owned $C):
   return %99 : $()
 }
 
-// A dead (ref_element_addr) projection is treated like a pointer
-// escape for convenience. Make sure the pointer escape bubbles up
-// through the phi and casts.
-//
 // CHECK-LABEL: testSSADeadRefElementAddr: ssa-liveness
 // CHECK: SSA lifetime analysis: %0 = argument of bb0 : $C
-// CHECK-NEXT: Incomplete liveness: Escaping address
 // CHECK-NEXT: bb0: LiveOut
 // CHECK-NEXT: bb2: LiveOut
 // CHECK-NEXT: bb3: LiveWithin
 // CHECK-NEXT: bb1: LiveOut
-// CHECK: last user:
-// CHECK-SAME: ref_element_addr %6 : $D, #D.object
+// CHECK: ref_element_addr %6 : $D, #D.object
 // CHECK-NEXT-LABEL: end running test 1 of 1 on testSSADeadRefElementAddr: ssa-liveness
 sil [ossa] @testSSADeadRefElementAddr : $@convention(thin) (@guaranteed C) -> () {
 bb0(%0 : @guaranteed $C):