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, 182 insertions, 0 deletions

diff --git a/test/wasm2js/br_table_hoisting.2asm.js.opt b/test/wasm2js/br_table_hoisting.2asm.js.opt
new file mode 100644
index 000000000..df70cc86f
--- /dev/null
+++ b/test/wasm2js/br_table_hoisting.2asm.js.opt
@@ -0,0 +1,182 @@
+
+function asmFunc(global, env, buffer) {
+ "almost asm";
+ var HEAP8 = new global.Int8Array(buffer);
+ var HEAP16 = new global.Int16Array(buffer);
+ var HEAP32 = new global.Int32Array(buffer);
+ var HEAPU8 = new global.Uint8Array(buffer);
+ var HEAPU16 = new global.Uint16Array(buffer);
+ var HEAPU32 = new global.Uint32Array(buffer);
+ var HEAPF32 = new global.Float32Array(buffer);
+ var HEAPF64 = new global.Float64Array(buffer);
+ var Math_imul = global.Math.imul;
+ var Math_fround = global.Math.fround;
+ var Math_abs = global.Math.abs;
+ var Math_clz32 = global.Math.clz32;
+ var Math_min = global.Math.min;
+ var Math_max = global.Math.max;
+ var Math_floor = global.Math.floor;
+ var Math_ceil = global.Math.ceil;
+ var Math_sqrt = global.Math.sqrt;
+ var abort = env.abort;
+ var nan = global.NaN;
+ var infinity = global.Infinity;
+ function zed($0) {
+  zed($0);
+ }
+ 
+ function $1($0) {
+  $0 = $0 | 0;
+  a : {
+   b : {
+    switch ($0 | 0) {
+    default:
+     zed(-1);
+     zed(-2);
+    case 3:
+     zed(-3);
+     zed(-4);
+    case 2:
+     zed(-5);
+     zed(-6);
+     break a;
+    case 0:
+     break a;
+    case 1:
+     break b;
+    };
+   }
+   zed(-7);
+   zed(-8);
+  }
+  zed(-9);
+  zed(-10);
+ }
+ 
+ function $2($0) {
+  $0 = $0 | 0;
+  a : {
+   b : {
+    c : {
+     d : {
+      switch ($0 | 0) {
+      default:
+       zed(-1);
+       zed(-2);
+       break c;
+      case 0:
+       break a;
+      case 1:
+       break b;
+      case 2:
+       break c;
+      case 3:
+       break d;
+      };
+     }
+     zed(-3);
+     zed(-4);
+    }
+    zed(-5);
+    zed(-6);
+    break a;
+   }
+   zed(-7);
+   zed(-8);
+  }
+  zed(-9);
+  zed(-10);
+ }
+ 
+ function $3($0) {
+  $0 = $0 | 0;
+  a : {
+   b : {
+    c : {
+     d : {
+      switch ($0 | 0) {
+      default:
+       if ($0) {
+        break c
+       }
+       zed(-1);
+       zed(-2);
+      case 0:
+       break a;
+      case 1:
+       break b;
+      case 2:
+       break c;
+      case 3:
+       break d;
+      };
+     }
+     zed(-3);
+     zed(-4);
+    }
+    zed(-5);
+    zed(-6);
+    break a;
+   }
+   zed(-7);
+   zed(-8);
+  }
+  zed(-9);
+  zed(-10);
+ }
+ 
+ function $4($0) {
+  $0 = $0 | 0;
+  a : {
+   b : {
+    c : {
+     if ($0) {
+      break c
+     }
+     d : {
+      switch ($0 | 0) {
+      default:
+       if ($0) {
+        break c
+       }
+       zed(-1);
+       zed(-2);
+      case 0:
+       break a;
+      case 1:
+       break b;
+      case 2:
+       break c;
+      case 3:
+       break d;
+      };
+     }
+     zed(-3);
+     zed(-4);
+    }
+    zed(-5);
+    zed(-6);
+    break a;
+   }
+   zed(-7);
+   zed(-8);
+  }
+  zed(-9);
+  zed(-10);
+ }
+ 
+ var FUNCTION_TABLE = [];
+ return {
+  "foo1": $1, 
+  "foo2": $2, 
+  "foo3": $3, 
+  "foo4": $4
+ };
+}
+
+var memasmFunc = new ArrayBuffer(65536);
+var retasmFunc = asmFunc({Math,Int8Array,Uint8Array,Int16Array,Uint16Array,Int32Array,Uint32Array,Float32Array,Float64Array,NaN,Infinity}, {abort:function() { throw new Error('abort'); }},memasmFunc);
+export var foo1 = retasmFunc.foo1;
+export var foo2 = retasmFunc.foo2;
+export var foo3 = retasmFunc.foo3;
+export var foo4 = retasmFunc.foo4;