wasm2js: avoid some slow operations when not optimizing (#2082)

Without this PR, wasm2js0.test_printf in emscripten took an extremely long time to compile.

Author: kripken

src/wasm2js.h

@@ -301,12 +301,14 @@ Ref Wasm2JSBuilder::processWasm(Module* wasm, Name funcName) {
     // Finally, get the code into the flat form we need for wasm2js itself, and
     // optimize that a little in a way that keeps flat property.
     runner.add("flatten");
-    runner.add("remove-unused-names");
-    runner.add("merge-blocks");
+    // Regardless of optimization level, run some simple optimizations to undo
+    // some of the effects of flattening.
     runner.add("simplify-locals-notee-nostructure");
-    // Coalescing is slow if we didn't run full optimizations earlier, so don't
-    // run it automatically.
+    // Some operations can be very slow if we didn't run full optimizations
+    // earlier, so don't run them automatically.
     if (options.optimizeLevel > 0) {
+      runner.add("remove-unused-names");
+      runner.add("merge-blocks");
       runner.add("coalesce-locals");
     }
     runner.add("reorder-locals");

test/wasm2js/block.2asm.js

@@ -34,19 +34,25 @@ function asmFunc(global, env, buffer) {
  }
 
  function $3() {
-  dummy();
-  dummy();
-  dummy();
-  dummy();
-  dummy();
-  dummy();
-  dummy();
+  block : {
+   dummy();
+   dummy();
+   dummy();
+   dummy();
+  }
+  block1 : {
+   dummy();
+   dummy();
+   dummy();
+  }
   return 8 | 0;
  }
 
  function $4() {
-  dummy();
-  dummy();
+  block : {
+   dummy();
+   dummy();
+  }
   return 9 | 0;
  }
 
@@ -125,14 +131,13 @@ function asmFunc(global, env, buffer) {
   $0 = 0;
   $1_1 = $0;
   block : {
-   $2_1 = 1;
-   break block;
+   block47 : {
+    $2_1 = 1;
+    break block;
+   }
   }
   $0 = $1_1 + $2_1 | 0;
   $5_1 = $0;
-  block49 : {
-   break block49;
-  }
   $0 = $5_1 + 2 | 0;
   $9_1 = $0;
   block50 : {
@@ -142,8 +147,10 @@ function asmFunc(global, env, buffer) {
   $0 = $9_1 + $10_1 | 0;
   $13_1 = $0;
   block51 : {
-   $14_1 = 8;
-   break block51;
+   block52 : {
+    $14_1 = 8;
+    break block51;
+   }
   }
   $0 = $13_1 + $14_1 | 0;
   return $0 | 0;

test/wasm2js/br.2asm.js

@@ -115,28 +115,34 @@ function asmFunc(global, env, buffer) {
  function $13() {
   var $0 = 0, $1_1 = 0, $3_1 = 0;
   block : {
-   $0 = 3;
-   break block;
+   loop_in : while (1) {
+    $0 = 3;
+    break block;
+   };
   }
   return $0 | 0;
  }
 
  function $14() {
   var $0 = 0, $1_1 = 0, $3_1 = 0;
   block : {
-   dummy();
-   $0 = 4;
-   break block;
+   loop_in : while (1) {
+    dummy();
+    $0 = 4;
+    break block;
+   };
   }
   return $0 | 0;
  }
 
  function $15() {
   var $0 = 0;
   block : {
-   dummy();
-   $0 = 5;
-   break block;
+   loop_in : while (1) {
+    dummy();
+    $0 = 5;
+    break block;
+   };
   }
   return $0 | 0;
  }
@@ -505,8 +511,10 @@ function asmFunc(global, env, buffer) {
  function $54() {
   var $0 = 0;
   block : {
-   $0 = 8;
-   break block;
+   block0 : {
+    $0 = 8;
+    break block;
+   }
   }
   return 1 + $0 | 0 | 0;
  }

test/wasm2js/br_if.2asm.js

@@ -50,9 +50,9 @@ function asmFunc(global, env, buffer) {
 
  function $3($0) {
   $0 = $0 | 0;
-  dummy();
-  dummy();
   block : {
+   dummy();
+   dummy();
    if ($0) {
     break block
    }
@@ -89,10 +89,10 @@ function asmFunc(global, env, buffer) {
  function $6($0) {
   $0 = $0 | 0;
   var $2_1 = 0;
-  dummy();
-  dummy();
-  $2_1 = 11;
   block : {
+   dummy();
+   dummy();
+   $2_1 = 11;
    if ($0) {
     break block
    }
@@ -103,33 +103,40 @@ function asmFunc(global, env, buffer) {
  function $7($0) {
   $0 = $0 | 0;
   block : {
-   if ($0) {
-    break block
-   }
-   return 2 | 0;
+   loop_in : while (1) {
+    if ($0) {
+     break block
+    }
+    return 2 | 0;
+   };
   }
   return 3 | 0;
  }
 
  function $8($0) {
   $0 = $0 | 0;
   block : {
-   dummy();
-   if ($0) {
-    break block
-   }
-   return 2 | 0;
+   loop_in : while (1) {
+    dummy();
+    if ($0) {
+     break block
+    }
+    return 2 | 0;
+   };
   }
   return 4 | 0;
  }
 
  function $9($0) {
   $0 = $0 | 0;
-  dummy();
   fake_return_waka123 : {
-   if ($0) {
-    break fake_return_waka123
-   }
+   loop_in : while (1) {
+    dummy();
+    if ($0) {
+     break fake_return_waka123
+    }
+    break loop_in;
+   };
   }
  }
 
@@ -164,10 +171,12 @@ function asmFunc(global, env, buffer) {
  function $12($0) {
   $0 = $0 | 0;
   var $2_1 = 0;
-  $2_1 = 8;
   block : {
-   if ($0) {
-    break block
+   block0 : {
+    $2_1 = 8;
+    if ($0) {
+     break block
+    }
    }
    $2_1 = 4 + 16 | 0;
   }
@@ -178,9 +187,11 @@ function asmFunc(global, env, buffer) {
   $0 = $0 | 0;
   var $2_1 = 0;
   block : {
-   $2_1 = 8;
-   if ($0) {
-    break block
+   block1 : {
+    $2_1 = 8;
+    if ($0) {
+     break block
+    }
    }
    $2_1 = 4;
    break block;
@@ -191,10 +202,12 @@ function asmFunc(global, env, buffer) {
  function $14($0) {
   $0 = $0 | 0;
   var $2_1 = 0;
-  $2_1 = 8;
   block : {
-   if ($0) {
-    break block
+   block2 : {
+    $2_1 = 8;
+    if ($0) {
+     break block
+    }
    }
    $2_1 = 4;
    if (1) {
@@ -208,10 +221,12 @@ function asmFunc(global, env, buffer) {
  function $15($0) {
   $0 = $0 | 0;
   var $2_1 = 0;
-  $2_1 = 8;
   block : {
-   if ($0) {
-    break block
+   block3 : {
+    $2_1 = 8;
+    if ($0) {
+     break block
+    }
    }
    $2_1 = 4;
    if (1) {
@@ -226,9 +241,11 @@ function asmFunc(global, env, buffer) {
   $0 = $0 | 0;
   var $2_1 = 0;
   block : {
-   $2_1 = 8;
-   if ($0) {
-    break block
+   block4 : {
+    $2_1 = 8;
+    if ($0) {
+     break block
+    }
    }
    $2_1 = 4;
    switch (1 | 0) {
@@ -243,9 +260,11 @@ function asmFunc(global, env, buffer) {
   $0 = $0 | 0;
   var $2_1 = 0;
   block : {
-   $2_1 = 8;
-   if ($0) {
-    break block
+   block5 : {
+    $2_1 = 8;
+    if ($0) {
+     break block
+    }
    }
    $2_1 = 4;
    switch (1 | 0) {

test/wasm2js/br_table.2asm.js

@@ -98,12 +98,6 @@ function asmFunc(global, env, buffer) {
 
  function $9($0) {
   $0 = $0 | 0;
-  block : {
-   switch ($0 | 0) {
-   default:
-    break block;
-   };
-  }
   return 22 | 0;
  }
 
@@ -12593,10 +12587,12 @@ function asmFunc(global, env, buffer) {
  function $20() {
   var $1_1 = 0, $2_1 = 0, $4_1 = 0;
   fake_return_waka123 : {
-   $1_1 = 3;
-   switch (0 | 0) {
-   default:
-    break fake_return_waka123;
+   loop_in : while (1) {
+    $1_1 = 3;
+    switch (0 | 0) {
+    default:
+     break fake_return_waka123;
+    };
    };
   }
   return $1_1 | 0;
@@ -12605,11 +12601,13 @@ function asmFunc(global, env, buffer) {
  function $21() {
   var $1_1 = 0, $2_1 = 0, $4_1 = 0;
   fake_return_waka123 : {
-   dummy();
-   $1_1 = 4;
-   switch (-1 | 0) {
-   default:
-    break fake_return_waka123;
+   loop_in : while (1) {
+    dummy();
+    $1_1 = 4;
+    switch (-1 | 0) {
+    default:
+     break fake_return_waka123;
+    };
    };
   }
   return $1_1 | 0;
@@ -12618,11 +12616,13 @@ function asmFunc(global, env, buffer) {
  function $22() {
   var $1_1 = 0;
   fake_return_waka123 : {
-   dummy();
-   $1_1 = 5;
-   switch (1 | 0) {
-   default:
-    break fake_return_waka123;
+   loop_in : while (1) {
+    dummy();
+    $1_1 = 5;
+    switch (1 | 0) {
+    default:
+     break fake_return_waka123;
+    };
    };
   }
   return $1_1 | 0;