wasm2js: Switch optimizations (#2141)

This pattern-matches towers of blocks + a br_table into a JS switch. This is much smaller in code size and also avoids heavy nesting that can exceed the recursion limits of JS parsers.

This is not enough yet, because it pattern-matches very specifically. In reality, switches can look slightly different. Followup PRs will extend this. For now, this passes the test suite (what passed before - not including the massive-switch tests) + fuzzing so it's a good start.

1 files changed, 6 insertions, 10 deletions

diff --git a/test/wasm2js/loop.2asm.js b/test/wasm2js/loop.2asm.js
index 1b5a05a33..ab7e7d825 100644
--- a/test/wasm2js/loop.2asm.js
+++ b/test/wasm2js/loop.2asm.js
@@ -235,19 +235,15 @@ function asmFunc(global, env, buffer) {
    };
   }
   block50 : {
-   loop_in51 : while (1) {
-    switch (0 | 0) {
-    default:
-     break block50;
-    };
+   loop_in51 : while (1) switch (0 | 0) {
+   default:
+    break block50;
    };
   }
   block52 : {
-   loop_in53 : while (1) {
-    switch (1 | 0) {
-    default:
-     break block52;
-    };
+   loop_in53 : while (1) switch (1 | 0) {
+   default:
+    break block52;
    };
   }
   return 19 | 0;