fix: Fix lifetime confusion in shadow stack pass (#2596)

Author: dcodeIO

src/passes/shadowstack.ts

@@ -174,9 +174,9 @@ function needsSlot(module: Module, value: ExpressionRef): bool {
   switch (_BinaryenExpressionGetId(value)) {
     // no need to stack null pointers
     case ExpressionId.Const: return !isConstZero(value);
-    // already kept in another slot
-    case ExpressionId.LocalGet:
-    case ExpressionId.LocalSet: return false; // tee
+    // note: can't omit a slot when assigning from another local since the other
+    // local might have shorter lifetime and become reassigned, say in a loop,
+    // then no longer holding on to the previous value in its stack slot.
   }
   return true;
 }

tests/compiler/NonNullable.debug.wat

@@ -142,13 +142,44 @@
   i32.const 0
   return
  )
+ (func $~start (type $none_=>_none)
+  call $start:NonNullable
+ )
+ (func $~stack_check (type $none_=>_none)
+  global.get $~lib/memory/__stack_pointer
+  global.get $~lib/memory/__data_end
+  i32.lt_s
+  if
+   i32.const 33152
+   i32.const 33200
+   i32.const 1
+   i32.const 1
+   call $~lib/builtins/abort
+   unreachable
+  end
+ )
  (func $~lib/string/String.__eq (type $i32_i32_=>_i32) (param $left i32) (param $right i32) (result i32)
   (local $leftLength i32)
+  (local $3 i32)
+  global.get $~lib/memory/__stack_pointer
+  i32.const 8
+  i32.sub
+  global.set $~lib/memory/__stack_pointer
+  call $~stack_check
+  global.get $~lib/memory/__stack_pointer
+  i64.const 0
+  i64.store $0
   local.get $left
   local.get $right
   i32.eq
   if
    i32.const 1
+   local.set $3
+   global.get $~lib/memory/__stack_pointer
+   i32.const 8
+   i32.add
+   global.set $~lib/memory/__stack_pointer
+   local.get $3
    return
   end
   local.get $left
@@ -163,40 +194,117 @@
   end
   if
    i32.const 0
+   local.set $3
+   global.get $~lib/memory/__stack_pointer
+   i32.const 8
+   i32.add
+   global.set $~lib/memory/__stack_pointer
+   local.get $3
    return
   end
   local.get $left
+  local.set $3
+  global.get $~lib/memory/__stack_pointer
+  local.get $3
+  i32.store $0
+  local.get $3
   call $~lib/string/String#get:length
   local.set $leftLength
   local.get $leftLength
   local.get $right
+  local.set $3
+  global.get $~lib/memory/__stack_pointer
+  local.get $3
+  i32.store $0
+  local.get $3
   call $~lib/string/String#get:length
   i32.ne
   if
    i32.const 0
+   local.set $3
+   global.get $~lib/memory/__stack_pointer
+   i32.const 8
+   i32.add
+   global.set $~lib/memory/__stack_pointer
+   local.get $3
    return
   end
   local.get $left
+  local.set $3
+  global.get $~lib/memory/__stack_pointer
+  local.get $3
+  i32.store $0
+  local.get $3
   i32.const 0
   local.get $right
+  local.set $3
+  global.get $~lib/memory/__stack_pointer
+  local.get $3
+  i32.store $0 offset=4
+  local.get $3
   i32.const 0
   local.get $leftLength
   call $~lib/util/string/compareImpl
   i32.eqz
+  local.set $3
+  global.get $~lib/memory/__stack_pointer
+  i32.const 8
+  i32.add
+  global.set $~lib/memory/__stack_pointer
+  local.get $3
   return
  )
  (func $~lib/string/String.__ne (type $i32_i32_=>_i32) (param $left i32) (param $right i32) (result i32)
+  (local $2 i32)
+  global.get $~lib/memory/__stack_pointer
+  i32.const 8
+  i32.sub
+  global.set $~lib/memory/__stack_pointer
+  call $~stack_check
+  global.get $~lib/memory/__stack_pointer
+  i64.const 0
+  i64.store $0
   local.get $left
+  local.set $2
+  global.get $~lib/memory/__stack_pointer
+  local.get $2
+  i32.store $0
+  local.get $2
   local.get $right
+  local.set $2
+  global.get $~lib/memory/__stack_pointer
+  local.get $2
+  i32.store $0 offset=4
+  local.get $2
   call $~lib/string/String.__eq
   i32.eqz
+  local.set $2
+  global.get $~lib/memory/__stack_pointer
+  i32.const 8
+  i32.add
+  global.set $~lib/memory/__stack_pointer
+  local.get $2
   return
  )
  (func $NonNullable/assertNonNull<~lib/string/String> (type $i32_=>_none) (param $t i32)
+  (local $1 i32)
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.sub
+  global.set $~lib/memory/__stack_pointer
+  call $~stack_check
+  global.get $~lib/memory/__stack_pointer
+  i32.const 0
+  i32.store $0
   i32.const 0
   i32.eqz
   drop
   local.get $t
+  local.set $1
+  global.get $~lib/memory/__stack_pointer
+  local.get $1
+  i32.store $0
+  local.get $1
   i32.const 0
   call $~lib/string/String.__ne
   i32.eqz
@@ -208,31 +316,42 @@
    call $~lib/builtins/abort
    unreachable
   end
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.add
+  global.set $~lib/memory/__stack_pointer
  )
  (func $NonNullable/safetyCheck<~lib/string/String|null> (type $i32_=>_none) (param $t i32)
+  (local $1 i32)
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.sub
+  global.set $~lib/memory/__stack_pointer
+  call $~stack_check
+  global.get $~lib/memory/__stack_pointer
+  i32.const 0
+  i32.store $0
   local.get $t
+  local.set $1
+  global.get $~lib/memory/__stack_pointer
+  local.get $1
+  i32.store $0
+  local.get $1
   i32.const 0
   call $~lib/string/String.__ne
   if
    local.get $t
+   local.set $1
+   global.get $~lib/memory/__stack_pointer
+   local.get $1
+   i32.store $0
+   local.get $1
    call $NonNullable/assertNonNull<~lib/string/String>
   end
- )
- (func $~start (type $none_=>_none)
-  call $start:NonNullable
- )
- (func $~stack_check (type $none_=>_none)
   global.get $~lib/memory/__stack_pointer
-  global.get $~lib/memory/__data_end
-  i32.lt_s
-  if
-   i32.const 33152
-   i32.const 33200
-   i32.const 1
-   i32.const 1
-   call $~lib/builtins/abort
-   unreachable
-  end
+  i32.const 4
+  i32.add
+  global.set $~lib/memory/__stack_pointer
  )
  (func $start:NonNullable (type $none_=>_none)
   (local $0 i32)