EscapeUtils: fix handling a raw pointer during up-walk

When walking up we shouldn't end up at a load where followLoads is false, because going from a (non-followLoads) address to a load always involves a class indirection.
There is one exception: loading a raw pointer

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/Utilities/EscapeUtils.swift

@@ -679,6 +679,14 @@ fileprivate struct EscapeWalker<V: EscapeVisitor> : ValueDefUseWalker,
     case let ap as ApplyInst:
       return walkUpApplyResult(apply: ap, path: path.with(knownType: nil))
     case is LoadInst, is LoadWeakInst, is LoadUnownedInst:
+      if !followLoads(at: path.projectionPath) {
+        // When walking up we shouldn't end up at a load where followLoads is false,
+        // because going from a (non-followLoads) address to a load always involves a class indirection.
+        // There is one exception: loading a raw pointer, e.g.
+        //   %l = load %a : $Builtin.RawPointer
+        //   %a = pointer_to_address %l           // the up-walk starts at %a
+        return isEscaping
+      }
       return walkUp(address: (def as! UnaryInstruction).operand,
                     path: path.with(followStores: true).with(knownType: nil))
     case let atp as AddressToPointerInst:

test/SILOptimizer/addr_escape_info.sil

@@ -500,6 +500,28 @@ bb0:
   return %7 : $()
 }
 
+// CHECK-LABEL: Address escape information for load_rawpointer:
+// CHECK:       value:  %5 = pointer_to_address %4 : $Builtin.RawPointer to [strict] $*Int
+// CHECK-NEXT:    ==>   %8 = apply %7(%5) : $@convention(thin) (@in Int) -> ()
+// CHECK:       End function load_rawpointer
+sil @load_rawpointer : $@convention(thin) () -> () {
+bb0:
+  %0 = alloc_stack $Int
+  %1 = address_to_pointer %0 : $*Int to $Builtin.RawPointer
+  %2 = alloc_stack $Builtin.RawPointer
+  store %1 to %2 : $*Builtin.RawPointer
+  %4 = load %2 : $*Builtin.RawPointer
+  %5 = pointer_to_address %4 : $Builtin.RawPointer to [strict] $*Int
+  fix_lifetime %5 : $*Int
+  %7 = function_ref @indirect_argument : $@convention(thin) (@in Int) -> ()
+  %8 = apply %7(%5) : $@convention(thin) (@in Int) -> ()
+  dealloc_stack %2 : $*Builtin.RawPointer
+  dealloc_stack %0 : $*Int
+  %r = tuple ()
+  return %r : $()
+}
+
+
 // CHECK-LABEL: Address escape information for test_addr_alias1:
 // CHECK:      pair 0 - 1
 // CHECK-NEXT:   %2 = ref_element_addr %0 : $XandIntClass, #XandIntClass.x