Update GetNextSpillIndex to support x32 port.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index bb2ecc06b8e4e374e838cf2847f08221ed9f8faa..955a92f029d8148a7354350ff361ee1ed27a7f73 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -331,6 +331,16 @@ void LAccessArgumentsAt::PrintDataTo(StringStream* stream) {
 
 
 int LPlatformChunk::GetNextSpillIndex(RegisterKind kind) {
+  if (kind == DOUBLE_REGISTERS && kDoubleSize == 2 * kPointerSize) {
+    // Skip a slot if for a double-width slot for x32 port.
+    spill_slot_count_++;
+    // The spill slot's address is at rbp - (index + 1) * kPointerSize -
+    // StandardFrameConstants::kFixedFrameSizeFromFp. kFixedFrameSizeFromFp is
+    // 2 * kPointerSize, if rbp is aligned at 8-byte boundary, the below "|= 1"
+    // will make sure the spilled doubles are aligned at 8-byte boundary.
+    // TODO(haitao): make sure rbp is aligned at 8-byte boundary for x32 port.
+    spill_slot_count_ |= 1;
+  }
   return spill_slot_count_++;
 }