[turbofan] More aggressive reuse of spill slots in the register allocator.

src/compiler/x64/code-generator-x64.cc

Index: src/compiler/x64/code-generator-x64.cc
diff --git a/src/compiler/x64/code-generator-x64.cc b/src/compiler/x64/code-generator-x64.cc
index e1eb92f12bb09436d57d519a771e40ffabacad46..3f9a20d061d655457df558ba8880f6d6b65dcdcf 100644
--- a/src/compiler/x64/code-generator-x64.cc
+++ b/src/compiler/x64/code-generator-x64.cc
@@ -1001,7 +1001,7 @@ void CodeGenerator::AssembleSwap(InstructionOperand* source,
     __ movsd(xmm0, src);
     __ movsd(src, dst);
     __ movsd(dst, xmm0);
-  } else if (source->IsDoubleRegister() && destination->IsDoubleRegister()) {
+  } else if (source->IsDoubleRegister() && destination->IsDoubleStackSlot()) {
     // XMM register-memory swap.  We rely on having xmm0
     // available as a fixed scratch register.
     XMMRegister src = g.ToDoubleRegister(source);