Convert float64 to float32 when coerced with a heapf32 assignment.

test/mjsunit/wasm/asm-wasm.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --expose-wasm
 
 function EmptyTest() {
   "use asm";
   function caller() {
     empty();
@@ skipping 1415 matching lines @@
       return +HEAPF32[0];
     }
     return {func: func};
   }
 
   var m = _WASMEXP_.instantiateModuleFromAsm(Module.toString());
   assertEquals(3, m.func());
 });  // TODO(bradnelson): Enable when Math.fround implementation lands.
 
 
+(function TestDoubleToFloatAssignment() {
+  function Module(stdlib, foreign, heap) {
+    "use asm";
+    var HEAPF32 = new stdlib.Float32Array(heap);
+    var fround = stdlib.Math.fround;
+    function func() {
+      var a = 1.23;
+      HEAPF32[0] = a;
+      return +HEAPF32[0];
+    }
+    return {func: func};
+  }
+
+  var m = _WASMEXP_.instantiateModuleFromAsm(Module.toString());
+  assertEquals(1.23, m.func());
+});
+
+
 (function TestIntegerMultiplyBothWays() {
   function Module(stdlib, foreign, heap) {
     "use asm";
     function func() {
       var a = 1;
       return ((a * 3) + (4 * a)) | 0;
     }
     return {func: func};
   }
 
@@ skipping 91 matching lines @@
       var a = 0;
       f = 5616315000.000001;
       a = ~~f >>>0;
       return a | 0;
     }
     return { main : aaa };
   }
   var wasm = _WASMEXP_.instantiateModuleFromAsm(asmModule.toString());
   assertEquals(1321347704, wasm.main());
 })();