X64: Use low bits of registers in emit_sse_operand. Enable --stop-at flag.

Review URL: http://codereview.chromium.org/155052

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2356 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/assembler-x64.cc

@@ -2022,11 +2022,11 @@ void Assembler::emit_sse_operand(XMMRegister reg, const Operand& adr) {
 
 
 void Assembler::emit_sse_operand(XMMRegister dst, XMMRegister src) {
-  emit(0xC0 | (dst.code() << 3) | src.code());
+  emit(0xC0 | (dst.low_bits() << 3) | src.low_bits());
 }
 
 void Assembler::emit_sse_operand(XMMRegister dst, Register src) {
-  emit(0xC0 | (dst.code() << 3) | src.code());
+  emit(0xC0 | (dst.low_bits() << 3) | src.low_bits());
 }
 
 

src/x64/assembler-x64.h

@@ -160,6 +160,17 @@ struct XMMRegister {
     return code_;
   }
 
+  // Return the high bit of the register code as a 0 or 1.  Used often
+  // when constructing the REX prefix byte.
+  int high_bit() const {
+    return code_ >> 3;
+  }
+  // Return the 3 low bits of the register code.  Used when encoding registers
+  // in modR/M, SIB, and opcode bytes.
+  int low_bits() const {
+    return code_ & 0x7;
+  }
+
   int code_;
 };
 

src/x64/codegen-x64.cc

@@ -154,8 +154,7 @@ void CodeGenerator::GenCode(FunctionLiteral* function) {
 
 #ifdef DEBUG
   if (strlen(FLAG_stop_at) > 0 &&
-      //    fun->name()->IsEqualTo(CStrVector(FLAG_stop_at))) {
-      false) {
+      function->name()->IsEqualTo(CStrVector(FLAG_stop_at))) {
     frame_->SpillAll();
     __ int3();
   }