Always encode floats as little-endian

Change-Id: I7dd05e5b5feffceb1dd3b2a055c308266aea7c94
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1995272Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Milad Farazmand <miladfar@ca.ibm.com>
Commit-Queue: Eric Leese <leese@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65702}

test/mjsunit/wasm/wasm-module-builder.js

@@ -3,10 +3,8 @@
 // found in the LICENSE file.
 
 // Used for encoding f32 and double constants to bits.
-let f32_view = new Float32Array(1);
-let f32_bytes_view = new Uint8Array(f32_view.buffer);
-let f64_view = new Float64Array(1);
-let f64_bytes_view = new Uint8Array(f64_view.buffer);
+let byte_view = new Uint8Array(8);
+let data_view = new DataView(byte_view.buffer);
 
 // The bytes function receives one of
 //  - several arguments, each of which is either a number or a string of length
@@ -1078,13 +1076,13 @@ class WasmModuleBuilder {
               break;
             case kWasmF32:
               section.emit_u8(kExprF32Const);
-              f32_view[0] = global.init;
-              section.emit_bytes(f32_bytes_view);
+              data_view.setFloat32(0, global.init, true);
+              section.emit_bytes(byte_view.subarray(0, 4));
               break;
             case kWasmF64:
               section.emit_u8(kExprF64Const);
-              f64_view[0] = global.init;
-              section.emit_bytes(f64_bytes_view);
+              data_view.setFloat64(0, global.init, true);
+              section.emit_bytes(byte_view);
               break;
             case kWasmAnyFunc:
             case kWasmAnyRef:
@@ -1423,18 +1421,18 @@ function wasmI32Const(val) {
 }
 
 function wasmF32Const(f) {
-  f32_view[0] = f;
+  // Write in little-endian order at offset 0.
+  data_view.setFloat32(0, f, true);
   return [
-    kExprF32Const, f32_bytes_view[0], f32_bytes_view[1], f32_bytes_view[2],
-    f32_bytes_view[3]
+    kExprF32Const, byte_view[0], byte_view[1], byte_view[2], byte_view[3]
   ];
 }
 
 function wasmF64Const(f) {
-  f64_view[0] = f;
+  // Write in little-endian order at offset 0.
+  data_view.setFloat64(0, f, true);
   return [
-    kExprF64Const, f64_bytes_view[0], f64_bytes_view[1], f64_bytes_view[2],
-    f64_bytes_view[3], f64_bytes_view[4], f64_bytes_view[5], f64_bytes_view[6],
-    f64_bytes_view[7]
+    kExprF64Const, byte_view[0], byte_view[1], byte_view[2],
+    byte_view[3], byte_view[4], byte_view[5], byte_view[6], byte_view[7]
   ];
 }