Avoid heap allocation for binary search work stack.

During switch lowering a binary search tree is created. The height of this tree is usually small so no need for heap allocation. BUG= R=jvoung@chromium.org, jvoung, stichnot Review URL: https://codereview.chromium.org/1240323005.

Avoid heap allocation for binary search work stack.
8447bbae · Andrew Scull · cb6e95aa · 8447bbae
Commit 8447bbae authored Jul 23, 2015 by Andrew Scull
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IceTargetLoweringX86BaseImpl.h src/IceTargetLoweringX86BaseImpl.h +2 -2

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--- a/src/IceTargetLoweringX86BaseImpl.h
+++ b/src/IceTargetLoweringX86BaseImpl.h
@@ -4698,8 +4698,8 @@ void TargetX86Base<Machine>::lowerSwitch(const InstSwitch *Inst) {
    SizeT Size;
    typename Traits::Insts::Label *Label;
  };
-  std::stack<SearchSpan, std::deque<SearchSpan, CfgLocalAllocator<SearchSpan>>>
-      SearchSpanStack;
+  // The stack will only grow to the height of the tree so 12 should be plenty
+  std::stack<SearchSpan, llvm::SmallVector<SearchSpan, 12>> SearchSpanStack;
  SearchSpanStack.emplace(0, CaseClusters.size(), nullptr);
  bool DoneCmp = false;