SIL: a few small changes in BasicBlockData

* Instead of passing the vector type as template argument, use a SmallVector and just pass the inline size
* Increase the inline size to 32. Found by experiment, this fits 90% of all functions.
* add an API for getting data for newly created blocks.

Author: eeckstein

include/swift/SIL/BasicBlockData.h

@@ -41,13 +41,13 @@ namespace swift {
 /// long as the invalidation mechanism ensures that the analysis data is not
 /// retrieved after the function's block list changed.
 ///
-/// The Vector template argument specifies how the data is stored. By default
-/// it's a SmallVector with an inline-size of 4. This avoids memory allocation
-/// for about 70% of all functions.
-template <typename Data, typename Vector = llvm::SmallVector<Data, 4>>
+/// The template argument \p N specifies how many Data elements can be stored
+/// inline in the data vector. The default value of 32 avoids malloc for about
+/// 90% of all functions.
+template <typename Data, unsigned N = 32>
 class BasicBlockData {
   SILFunction *function;
-  Vector data;
+  llvm::SmallVector<Data, N> data;
 
   /// The data is valid if validForBlockOrder matches the function's
   /// BlockListChangeIdx.
@@ -200,6 +200,19 @@ class BasicBlockData {
   const Data &operator[] (SILBasicBlock *block) const {
     return data[getIndex(block)];
   }
+  
+  /// If \p block is a new block, i.e. created after this BasicBlockData was
+  /// constructed, creates a new Data with \p init and returns it.
+  Data &get(SILBasicBlock *block, llvm::function_ref<Data()> init) {
+    if (block->index < 0) {
+      assert(validForBlockOrder == function->BlockListChangeIdx &&
+             "BasicBlockData invalid because the function's block list changed");
+      validForBlockOrder = ++function->BlockListChangeIdx;
+      block->index = data.size();
+      data.push_back(init());
+    }
+    return data[getIndex(block)];
+  }
 };
 
 } // end swift namespace

include/swift/SIL/SILBasicBlock.h

@@ -35,7 +35,7 @@ public llvm::ilist_node<SILBasicBlock>, public SILAllocated<SILBasicBlock> {
   friend class SILSuccessor;
   friend class SILFunction;
   friend class SILGlobalVariable;
-  template <typename Data, typename Vector> friend class BasicBlockData;
+  template <typename, unsigned> friend class BasicBlockData;
   friend class BasicBlockBitfield;
 
 public:

include/swift/SIL/SILFunction.h

@@ -148,7 +148,7 @@ class SILFunction
   friend class SILBasicBlock;
   friend class SILModule;
   friend class SILFunctionBuilder;
-  template <typename Data, typename Vector> friend class BasicBlockData;
+  template <typename, unsigned> friend class BasicBlockData;
   friend class BasicBlockBitfield;
 
   /// Module - The SIL module that the function belongs to.