[wasm] Fix I32ReinterpretF32 and I64ReinterpretF64 on ia32.

src/wasm/function-body-decoder.h

Index: src/wasm/function-body-decoder.h
diff --git a/src/wasm/function-body-decoder.h b/src/wasm/function-body-decoder.h
index 836dda4b44a9c4408f85aab006237cc6d30e2e3a..56df26759b0a48a1e5a46208a435422fcb2e4733 100644
--- a/src/wasm/function-body-decoder.h
+++ b/src/wasm/function-body-decoder.h
@@ -70,7 +70,9 @@ struct ImmF32Operand {
   float value;
   unsigned length;
   inline ImmF32Operand(Decoder* decoder, const byte* pc) {
-    value = bit_cast<float>(decoder->checked_read_u32(pc, 1, "immf32"));
+    // Do not use bit_cast to preserve a potential signalling bit of a NaN.

[titzer, 2017/01/19 13:13:01]

Comment is a little misleading (since it might be parsed as meaning the
opposite).

Might read better as "avoid bit_cast because it might not preserve the signaling
bit of a NaN"

[ahaas, 2017/01/19 15:46:19]

Done.

+    uint32_t tmp = decoder->checked_read_u32(pc, 1, "immf32");
+    value = *reinterpret_cast<float*>(&tmp);
     length = 4;
   }
 };
@@ -79,7 +81,9 @@ struct ImmF64Operand {
   double value;
   unsigned length;
   inline ImmF64Operand(Decoder* decoder, const byte* pc) {
-    value = bit_cast<double>(decoder->checked_read_u64(pc, 1, "immf64"));
+    // Do not use bit_cast to preserve a potential signalling bit of a NaN.
+    uint64_t tmp = decoder->checked_read_u64(pc, 1, "immf64");
+    value = *reinterpret_cast<double*>(&tmp);
     length = 8;
   }
 };