[CaptureTracker] Provide an ordered basic block to PointerMayBeCapturedBefore

This patch is a follow up from r240560 and is a step further into
mitigating the compile time performance issues in CaptureTracker.

By providing the CaptureTracker with a "cached ordered basic block"
instead of computing it every time, MemDepAnalysis can use this cache
throughout its calls to AA->callCapturesBefore, avoiding to recompute it
for every scanned instruction. In the same testcase used in r240560,
compile time is reduced from 2min to 30s.

This also fixes PR22348.

rdar://problem/19230319
Differential Revision: http://reviews.llvm.org/D11364

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243750 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/OrderedBasicBlock.h

@@ -0,0 +1,66 @@
+//===- llvm/Analysis/OrderedBasicBlock.h --------------------- -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the OrderedBasicBlock class. OrderedBasicBlock maintains
+// an interface where clients can query if one instruction comes before another
+// in a BasicBlock. Since BasicBlock currently lacks a reliable way to query
+// relative position between instructions one can use OrderedBasicBlock to do
+// such queries. OrderedBasicBlock is lazily built on a source BasicBlock and
+// maintains an internal Instruction -> Position map. A OrderedBasicBlock
+// instance should be discarded whenever the source BasicBlock changes.
+//
+// It's currently used by the CaptureTracker in order to find relative
+// positions of a pair of instructions inside a BasicBlock.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_ORDEREDBASICBLOCK_H
+#define LLVM_ANALYSIS_ORDEREDBASICBLOCK_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/IR/BasicBlock.h"
+
+namespace llvm {
+
+class Instruction;
+class BasicBlock;
+
+class OrderedBasicBlock {
+private:
+  /// \brief Map a instruction to its position in a BasicBlock.
+  SmallDenseMap<const Instruction *, unsigned, 32> NumberedInsts;
+
+  /// \brief Keep track of last instruction inserted into \p NumberedInsts.
+  /// It speeds up queries for uncached instructions by providing a start point
+  /// for new queries in OrderedBasicBlock::comesBefore.
+  BasicBlock::const_iterator LastInstFound;
+
+  /// \brief The position/number to tag the next instruction to be found.
+  unsigned NextInstPos;
+
+  /// \brief The source BasicBlock to map.
+  const BasicBlock *BB;
+
+  /// \brief Given no cached results, find if \p A comes before \p B in \p BB.
+  /// Cache and number out instruction while walking \p BB.
+  bool comesBefore(const Instruction *A, const Instruction *B);
+
+public:
+  OrderedBasicBlock(const BasicBlock *BasicB);
+
+  /// \brief Find out whether \p A dominates \p B, meaning whether \p A
+  /// comes before \p B in \p BB. This is a simplification that considers
+  /// cached instruction positions and ignores other basic blocks, being
+  /// only relevant to compare relative instructions positions inside \p BB.
+  bool dominates(const Instruction *A, const Instruction *B);
+};
+
+} // End llvm namespace
+
+#endif