[BFI] Add new LazyBFI analysis pass

Summary:
This is necessary for D21771.  In order to add the hotness attribute to
optimization remarks we need BFI to be available in all passes that emit
optimization remarks.

However we don't want to pay for computing BFI unless the hotness
attribute is requested.

This is achieved by making BFI lazy at the very high-level through a new
analysis pass -- BFI is not calculated unless requested.

I am adding a test to check the laziness under D21771 where the first
user of the analysis is added.

Reviewers: hfinkel, dexonsmith, davidxl

Subscribers: davidxl, dexonsmith, llvm-commits

Differential Revision: http://reviews.llvm.org/D22141

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275250 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 128 insertions, 0 deletions

diff --git a/include/llvm/Analysis/BlockFrequencyInfo.h b/include/llvm/Analysis/BlockFrequencyInfo.h
index ed473abf3b3..7d48dfc9121 100644
--- a/include/llvm/Analysis/BlockFrequencyInfo.h
+++ b/include/llvm/Analysis/BlockFrequencyInfo.h
@@ -43,6 +43,8 @@ public:
 
   BlockFrequencyInfo &operator=(BlockFrequencyInfo &&RHS);
 
+  ~BlockFrequencyInfo();
+
   const Function *getFunction() const;
   const BranchProbabilityInfo *getBPI() const;
   void view() const;
diff --git a/include/llvm/Analysis/LazyBlockFrequencyInfo.h b/include/llvm/Analysis/LazyBlockFrequencyInfo.h
new file mode 100644
index 00000000000..a2d24bb9eb8
--- /dev/null
+++ b/include/llvm/Analysis/LazyBlockFrequencyInfo.h
@@ -0,0 +1,125 @@
+//===- LazyBlockFrequencyInfo.h - Lazy Block Frequency Analysis -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This is an alternative analysis pass to BlockFrequencyInfoWrapperPass.  The
+// difference is that with this pass the block frequencies are not computed when
+// the analysis pass is executed but rather when the BFI results is explicitly
+// requested by the analysis client.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_LAZYBLOCKFREQUENCYINFO_H
+#define LLVM_ANALYSIS_LAZYBLOCKFREQUENCYINFO_H
+
+#include "llvm/Analysis/BlockFrequencyInfo.h"
+#include "llvm/Pass.h"
+
+namespace llvm {
+class AnalysisUsage;
+class BranchProbabilityInfo;
+class Function;
+class LoopInfo;
+
+/// \brief This is an alternative analysis pass to
+/// BlockFrequencyInfoWrapperPass.  The difference is that with this pass the
+/// block frequencies are not computed when the analysis pass is executed but
+/// rather when the BFI results is explicitly requested by the analysis client.
+///
+/// There are some additional requirements for any client pass that wants to use
+/// the analysis:
+///
+/// 1. The pass needs to initialize dependent passes with:
+///
+///   INITIALIZE_PASS_DEPENDENCY(LazyBFIPass)
+///
+/// 2. Similarly, getAnalysisUsage should call:
+///
+///   LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU)
+///
+/// 3. The computed BFI should be requested with
+///    getAnalysis<LazyBlockFrequencyInfoPass>().getBFI() before either LoopInfo
+///    or BPI could be invalidated for example by changing the CFG.
+///
+/// Note that it is expected that we wouldn't need this functionality for the
+/// new PM since with the new PM, analyses are executed on demand.
+class LazyBlockFrequencyInfoPass : public FunctionPass {
+
+  /// Wraps a BFI to allow lazy computation of the block frequencies.
+  ///
+  /// A pass that only conditionally uses BFI can uncondtionally require the
+  /// analysis without paying for the overhead if BFI doesn't end up being used.
+  class LazyBlockFrequencyInfo {
+  public:
+    LazyBlockFrequencyInfo()
+        : Calculated(false), F(nullptr), BPI(nullptr), LI(nullptr) {}
+
+    /// Set up the per-function input.
+    void setAnalysis(const Function *F, const BranchProbabilityInfo *BPI,
+                     const LoopInfo *LI) {
+      this->F = F;
+      this->BPI = BPI;
+      this->LI = LI;
+    }
+
+    /// Retrieve the BFI with the block frequencies computed.
+    BlockFrequencyInfo &getCalculated() {
+      if (!Calculated) {
+        assert(F && BPI && LI && "call setAnalysis");
+        BFI.calculate(*F, *BPI, *LI);
+        Calculated = true;
+      }
+      return BFI;
+    }
+
+    const BlockFrequencyInfo &getCalculated() const {
+      return const_cast<LazyBlockFrequencyInfo *>(this)->getCalculated();
+    }
+
+    void releaseMemory() {
+      BFI.releaseMemory();
+      Calculated = false;
+      setAnalysis(nullptr, nullptr, nullptr);
+    }
+
+  private:
+    BlockFrequencyInfo BFI;
+    bool Calculated;
+    const Function *F;
+    const BranchProbabilityInfo *BPI;
+    const LoopInfo *LI;
+  };
+
+  LazyBlockFrequencyInfo LBFI;
+
+public:
+  static char ID;
+
+  LazyBlockFrequencyInfoPass();
+
+  /// \brief Compute and return the block frequencies.
+  BlockFrequencyInfo &getBFI() { return LBFI.getCalculated(); }
+
+  /// \brief Compute and return the block frequencies.
+  const BlockFrequencyInfo &getBFI() const { return LBFI.getCalculated(); }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
+
+  /// Helper for client passes to set up the analysis usage on behalf of this
+  /// pass.
+  static void getLazyBFIAnalysisUsage(AnalysisUsage &AU);
+
+  bool runOnFunction(Function &F) override;
+  void releaseMemory() override;
+  void print(raw_ostream &OS, const Module *M) const override;
+};
+
+/// \brief Helper for client passes to initialize dependent passes for LBFI.
+void initializeLazyBFIPassPass(PassRegistry &Registry);
+}
+#endif
diff --git a/include/llvm/InitializePasses.h b/include/llvm/InitializePasses.h
index 12de6310c5f..59ee09432ee 100644
--- a/include/llvm/InitializePasses.h
+++ b/include/llvm/InitializePasses.h
@@ -160,6 +160,7 @@ void initializeIntervalPartitionPass(PassRegistry&);
 void initializeJumpThreadingPass(PassRegistry&);
 void initializeLCSSAWrapperPassPass(PassRegistry &);
 void initializeLegacyLICMPassPass(PassRegistry&);
+void initializeLazyBlockFrequencyInfoPassPass(PassRegistry&);
 void initializeLazyValueInfoWrapperPassPass(PassRegistry&);
 void initializeLintPass(PassRegistry&);
 void initializeLiveDebugValuesPass(PassRegistry&);