Give names to some locals and params in wat

Also add some comments

Author: yamt

test/testsuite/wasi_threads_exit_main_block.wat

@@ -1,5 +1,8 @@
 ;; When the main thread calls proc_exit, it should terminate
 ;; a thread blocking in `memory.atomic.wait32` opecode.
+;;
+;; linear memory usage:
+;;   0: notify/wait
 
 (module
   (memory (export "memory") (import "foo" "bar") 1 1 shared)

test/testsuite/wasi_threads_exit_main_busy.wat

@@ -1,5 +1,8 @@
 ;; When the main thread calls proc_exit, it should terminate
 ;; a busy-looping thread.
+;;
+;; linear memory usage:
+;;   0: wait
 
 (module
   (memory (export "memory") (import "foo" "bar") 1 1 shared)

test/testsuite/wasi_threads_exit_main_wasi.wat

@@ -1,5 +1,11 @@
 ;; When the main thread calls proc_exit, it should terminate
 ;; a thread blocking in a WASI call. (poll_oneoff)
+;;
+;; linear memory usage:
+;;   0: wait
+;;   100: poll_oneoff subscription
+;;   200: poll_oneoff event
+;;   300: poll_oneoff return value
 
 (module
   (memory (export "memory") (import "foo" "bar") 1 1 shared)

test/testsuite/wasi_threads_exit_nonmain_block.wat

@@ -1,5 +1,8 @@
 ;; When a non-main thread calls proc_exit, it should terminate
 ;; the main thread blocking in `memory.atomic.wait32` opecode.
+;;
+;; linear memory usage:
+;;   0: wait
 
 (module
   (memory (export "memory") (import "foo" "bar") 1 1 shared)

test/testsuite/wasi_threads_exit_nonmain_busy.wat

@@ -1,5 +1,8 @@
 ;; When a non-main thread calls proc_exit, it should terminate
 ;; the main thread which is busy-looping.
+;;
+;; linear memory usage:
+;;   0: wait
 
 (module
   (memory (export "memory") (import "foo" "bar") 1 1 shared)

test/testsuite/wasi_threads_exit_nonmain_wasi.wat

@@ -1,5 +1,11 @@
 ;; When a non-main thread calls proc_exit, it should terminate
 ;; the main thread which is blocking in a WASI call. (poll_oneoff)
+;;
+;; linear memory usage:
+;;   0: wait
+;;   100: poll_oneoff subscription
+;;   200: poll_oneoff event
+;;   300: poll_oneoff return value
 
 (module
   (memory (export "memory") (import "foo" "bar") 1 1 shared)

test/testsuite/wasi_threads_spawn.wat

@@ -1,17 +1,22 @@
 ;; Create a thread with thread-spawn and perform a few sanity checks.
 
+;; linear memory usage:
+;;   0: notify/wait
+;;   4: tid
+;;   8: user_arg
+
 (module
   (memory (export "memory") (import "foo" "bar") 1 1 shared)
   (func $thread_spawn (import "wasi" "thread_spawn") (param i32) (result i32))
   (func $proc_exit (import "wasi_snapshot_preview1" "proc_exit") (param i32))
-  (func (export "wasi_thread_start") (param i32 i32)
+  (func (export "wasi_thread_start") (param $tid i32) (param $user_arg i32)
     ;; store tid
     i32.const 4
-    local.get 0
+    local.get $tid
     i32.store
     ;; store user pointer
     i32.const 8
-    local.get 1
+    local.get $user_arg
     i32.store
     ;; notify the main
     i32.const 0
@@ -23,12 +28,12 @@
     drop
     ;; returning from wasi_thread_start terminates only this thread
   )
-  (func (export "_start") (local i32)
+  (func (export "_start") (local $tid i32)
     ;; spawn a thread
     i32.const 12345  ;; user pointer
     call $thread_spawn
     ;; check error
-    local.tee 0 ;; save the tid to check later
+    local.tee $tid ;; save the tid to check later
     i32.const 0
     i32.le_s
     if
@@ -46,7 +51,7 @@
       unreachable
     end
     ;; check the tid
-    local.get 0
+    local.get $tid
     i32.const 4
     i32.load
     i32.ne