[wasm] vm.c: stop unwinding to main for every vm_exec call by setjmp

the original rb_wasm_setjmp implementation always unwinds to the root
call frame to have setjmp compatible interface, and simulate sjlj's
undefined behavior. Therefore, every vm_exec call unwinds to main, and
a deep call stack makes setjmp call very expensive. The following
snippet from optcarrot takes 5s even though it takes less than 0.3s on
native.

```
[0x0, 0x4, 0x8, 0xc].map do |attr|
  (0..7).map do |j|
    (0...0x10000).map do |i|
      clr = i[15 - j] * 2 + i[7 - j]
      clr != 0 ? attr | clr : 0
    end
  end
end
```

This patch adds a WASI specialized vm_exec which uses lightweight
try-catch API without unwinding to the root frame. After this patch, the
above snippet takes only 0.5s.

1 files changed, 70 insertions, 0 deletions

diff --git a/wasm/setjmp.c b/wasm/setjmp.c
index 3f017e202a..1e69cb1c64 100644
--- a/wasm/setjmp.c
+++ b/wasm/setjmp.c
@@ -57,6 +57,7 @@ async_buf_init(struct __rb_wasm_asyncify_jmp_buf* buf)
 
 // Global unwinding/rewinding jmpbuf state
 static rb_wasm_jmp_buf *_rb_wasm_active_jmpbuf;
+void *rb_asyncify_unwind_buf;
 
 __attribute__((noinline))
 int
@@ -106,6 +107,75 @@ _rb_wasm_longjmp(rb_wasm_jmp_buf* env, int value)
     asyncify_start_unwind(&env->longjmp_buf);
 }
 
+
+enum try_catch_phase {
+  TRY_CATCH_PHASE_MAIN   = 0,
+  TRY_CATCH_PHASE_RESCUE = 1,
+};
+
+void
+rb_wasm_try_catch_init(struct rb_wasm_try_catch *try_catch,
+                       rb_wasm_try_catch_func_t try_f,
+                       rb_wasm_try_catch_func_t catch_f,
+                       void *context)
+{
+    try_catch->state = TRY_CATCH_PHASE_MAIN;
+    try_catch->try_f = try_f;
+    try_catch->catch_f = catch_f;
+    try_catch->context = context;
+}
+
+// NOTE: This function is not processed by Asyncify due to a call of asyncify_stop_rewind
+void
+rb_wasm_try_catch_loop_run(struct rb_wasm_try_catch *try_catch, rb_wasm_jmp_buf *target)
+{
+    extern void *rb_asyncify_unwind_buf;
+    extern rb_wasm_jmp_buf *_rb_wasm_active_jmpbuf;
+
+    target->state = JMP_BUF_STATE_CAPTURED;
+
+    switch ((enum try_catch_phase)try_catch->state) {
+    case TRY_CATCH_PHASE_MAIN: {
+        // may unwind
+        try_catch->try_f(try_catch->context);
+        break;
+    }
+    case TRY_CATCH_PHASE_RESCUE: {
+        if (try_catch->catch_f) {
+            // may unwind
+            try_catch->catch_f(try_catch->context);
+        }
+        break;
+    }
+    }
+
+    while (1) {
+        // catch longjmp with target jmp_buf
+        if (rb_asyncify_unwind_buf && _rb_wasm_active_jmpbuf == target) {
+            // do similar steps setjmp does when JMP_BUF_STATE_RETURNING
+
+            // stop unwinding
+            // (but call stop_rewind to update the asyncify state to "normal" from "unwind")
+            asyncify_stop_rewind();
+            // clear the active jmpbuf because it's already stopped
+            _rb_wasm_active_jmpbuf = NULL;
+            // reset jmpbuf state to be able to unwind again
+            target->state = JMP_BUF_STATE_CAPTURED;
+            // move to catch loop phase
+            try_catch->state = TRY_CATCH_PHASE_RESCUE;
+            if (try_catch->catch_f) {
+                try_catch->catch_f(try_catch->context);
+            }
+            continue;
+        } else if (rb_asyncify_unwind_buf /* unrelated unwind */) {
+            return;
+        }
+        // no unwind, then exit
+        break;
+    }
+    return;
+}
+
 void *
 rb_wasm_handle_jmp_unwind(void)
 {