We can avoid spilling live ranges with spill ranges when we have

sufficient physical registers for all the virtual registers.

This should come in handy for frame elision. There, I noticed that even
for very small functions (==very few virtual registers), because we spill
the context/function marker ranges, we lose the frame elision
opportunity.

There is a subsequent change needed to fully help frame elision -
decoupling spilling of context & function marker from prologue.

BUG=

Review URL: https://codereview.chromium.org/1469743002

Cr-Commit-Position: refs/heads/master@{#32221}

src/compiler/register-allocator.cc

@@ -2432,7 +2432,8 @@ void LinearScanAllocator::AllocateRegisters() {
   DCHECK(active_live_ranges().empty());
   DCHECK(inactive_live_ranges().empty());
 
-  SplitAndSpillRangesDefinedByMemoryOperand(false);
+  SplitAndSpillRangesDefinedByMemoryOperand(code()->VirtualRegisterCount() <=
+                                            num_allocatable_registers());
 
   for (TopLevelLiveRange* range : data()->live_ranges()) {
     if (!CanProcessRange(range)) continue;