[PassManager] Tuning Memory Usage of AnalysisUsage

We were using unneccessarily large initial sizes for these SmallVectors.  This was wasting around 50kb of memory for the O3 pipeline, even after the uniquing changes.  We're still using around 20kb which is a bit much, but it's definitely better.  This is about a 6% improvement in total O3 memory usage.

Note: The raw data on structure size which were used to pick these thresholds can be found in the review thread.

Differential Revision: http://reviews.llvm.org/D15244

llvm-svn: 254974

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/include/llvm/PassAnalysisSupport.h b/llvm/include/llvm/PassAnalysisSupport.h
index f6265b62cbf..492a4ef464f 100644
--- a/llvm/include/llvm/PassAnalysisSupport.h
+++ b/llvm/include/llvm/PassAnalysisSupport.h
@@ -36,11 +36,17 @@ namespace llvm {
 ///
 class AnalysisUsage {
 public:
-  typedef SmallVector<AnalysisID, 32> VectorType;
+  typedef SmallVectorImpl<AnalysisID> VectorType;
 
 private:
   /// Sets of analyses required and preserved by a pass
-  VectorType Required, RequiredTransitive, Preserved, Used;
+  // TODO: It's not clear that SmallVector is an appropriate data structure for
+  // this usecase.  The sizes were picked to minimize wasted space, but are
+  // otherwise fairly meaningless.
+  SmallVector<AnalysisID, 8> Required;
+  SmallVector<AnalysisID, 2> RequiredTransitive;
+  SmallVector<AnalysisID, 2> Preserved;
+  SmallVector<AnalysisID, 0> Used;
   bool PreservesAll;
 
 public: