Introduce x87 port

src/code-stubs-hydrogen.cc

Index: src/code-stubs-hydrogen.cc
diff --git a/src/code-stubs-hydrogen.cc b/src/code-stubs-hydrogen.cc
index addc83d0f4cac9c0ac9847b809a2d4df6593dcdf..301e94b8feaf11971f5581d40f95941a5c2f14c5 100644
--- a/src/code-stubs-hydrogen.cc
+++ b/src/code-stubs-hydrogen.cc
@@ -333,7 +333,9 @@ HValue* CodeStubGraphBuilder<FastCloneShallowArrayStub>::BuildCodeStub() {
 
   // This stub is very performance sensitive, the generated code must be tuned
   // so that it doesn't build and eager frame.
+#if !defined(V8_TARGET_ARCH_X87)

[Weiliang, 2014/05/20 05:44:02]

x87 is more easy to spill the double register, so disable it.

[Sven Panne, 2014/05/20 06:21:20]

Please don't introduce any platform-specific #ifdefs into the non-platform
specific parts. I know that we already have a few of them, but we really need to
get rid of them, and don't introduce any more of them. In my POV, this is a
blocker for this CL.

[danno, 2014/05/20 08:18:55]

Yes, this platform-specific define here is a no-go. This is a good example why
we removed the x87 port in the first place, precisely because it is more work to
ensure that there is no frame generated on performance-sensitive stubs, and
since x87 ins't a core platform, it wasn't worth investing the effort. In any
case, you'll need to solve this in a platform independent way, e.g. fixing the
x87 register allocator to avoid having to generate the frame.

[Weiliang, 2014/05/20 08:41:06]

Yes, Thanks a lot for both of you comments. 

To best solve this issue, we would better fix the X87 register allocator to
avoid spilling the double registers. But currently X87 only has rudimentary
X87Stack tracking and in general it cannot handle phi-nodes (comments from
code).I did a very initial try to enhance it, but it seems to take some time.
After considering that this issue only break "x87.debug snapshot=on", I can
remove the code here and hope the CL could land firstly. And then we will
enhance the register allocator to fix this issue. Is it OK?
On 2014/05/20 08:18:55, danno wrote:

[danno, 2014/05/20 12:23:29]

I think it's fine to only support snapshot=off for now for x87, that was the
case for arm64 for a while before the port was complete. Yes, and please remove
the #ifdef here.

   info()->MarkMustNotHaveEagerFrame();
+#endif
 
   HInstruction* allocation_site = Add<HLoadKeyed>(GetParameter(0),
                                                   GetParameter(1),