[turbofan] delay inserting spill slots for parent ranges.

test/unittests/compiler/register-allocator-unittest.cc

Index: test/unittests/compiler/register-allocator-unittest.cc
diff --git a/test/unittests/compiler/register-allocator-unittest.cc b/test/unittests/compiler/register-allocator-unittest.cc
index 038a016ffde8ec102cf2c97e275d98881448e1f0..44d4fefe0311177891828051e0607b0caf74913b 100644
--- a/test/unittests/compiler/register-allocator-unittest.cc
+++ b/test/unittests/compiler/register-allocator-unittest.cc
@@ -152,7 +152,7 @@ TEST_F(RegisterAllocatorTest, DoubleDiamondManyRedundantPhis) {
   StartBlock();
   VReg vals[kPhis];
   for (int i = 0; i < kPhis; ++i) {
-    vals[i] = Parameter(Slot(i));
+    vals[i] = Parameter(Slot(-1 - i));
   }
   EndBlock(Branch(Reg(DefineConstant()), 1, 2));