handle asm.js globals that are set and the return value used

2 files changed, 15 insertions, 1 deletions

diff --git a/src/asm2wasm.h b/src/asm2wasm.h
index 52598ad0b..321d5275e 100644
--- a/src/asm2wasm.h
+++ b/src/asm2wasm.h
@@ -1014,7 +1014,10 @@ Function* Asm2WasmBuilder::processFunction(Ref ast) {
         }
         // global var
         assert(mappedGlobals.find(name) != mappedGlobals.end());
-        return builder.makeSetGlobal(name, process(ast[3]));
+        auto* ret = builder.makeSetGlobal(name, process(ast[3]));
+        // set_global does not return; if our value is trivially not used, don't emit a load (if nontrivially not used, opts get it later)
+        if (astStackHelper.getParent()[0] == STAT) return ret;
+        return builder.makeSequence(ret, builder.makeGetGlobal(name, ret->value->type));
       } else if (ast[2][0] == SUB) {
         Ref target = ast[2];
         assert(target[1][0] == NAME);
diff --git a/test/unit.asm.js b/test/unit.asm.js
index d6d0a27e8..cf2060030 100644
--- a/test/unit.asm.js
+++ b/test/unit.asm.js
@@ -281,6 +281,17 @@ function asm(global, env, buffer) {
     return phi() | 0;
   }
 
+  function useSetGlobal() {
+    var x = 0;
+    x = (Int = 10);
+    Int = 20;
+    return (Int = 30) | 0;
+  }
+
+  function usesSetGlobal2() {
+    return (Int = 40, 50) | 0;
+  }
+
   function z() {
   }
   function w() {