Refactor indirect call promotion profitability analysis (NFC)

Summary:
Refactored the profitability analysis out of the IC promotion pass and
into lib/Analysis so that it can be accessed by the summary index
builder in a follow-on patch to enable IC promotion in ThinLTO (D21932).

Reviewers: davidxl, xur

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D22182

llvm-svn: 275216

1 files changed, 110 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/IndirectCallPromotionAnalysis.cpp b/llvm/lib/Analysis/IndirectCallPromotionAnalysis.cpp
new file mode 100644
index 00000000000..b3941a4004a
--- /dev/null
+++ b/llvm/lib/Analysis/IndirectCallPromotionAnalysis.cpp
@@ -0,0 +1,110 @@
+//===-- IndirectCallPromotionAnalysis.cpp - Find promotion candidates ===//
+//
+//                      The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Helper methods for identifying profitable indirect call promotion
+// candidates for an instruction when the indirect-call value profile metadata
+// is available.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/IndirectCallPromotionAnalysis.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Analysis/IndirectCallSiteVisitor.h"
+#include "llvm/IR/CallSite.h"
+#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/InstVisitor.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/ProfileData/InstrProf.h"
+#include "llvm/Support/Debug.h"
+#include <string>
+#include <utility>
+#include <vector>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "pgo-icall-prom-analysis"
+
+// The minimum call count for the direct-call target to be considered as the
+// promotion candidate.
+static cl::opt<unsigned>
+    ICPCountThreshold("icp-count-threshold", cl::Hidden, cl::ZeroOrMore,
+                      cl::init(1000),
+                      cl::desc("The minimum count to the direct call target "
+                               "for the promotion"));
+
+// The percent threshold for the direct-call target (this call site vs the
+// total call count) for it to be considered as the promotion target.
+static cl::opt<unsigned>
+    ICPPercentThreshold("icp-percent-threshold", cl::init(33), cl::Hidden,
+                        cl::ZeroOrMore,
+                        cl::desc("The percentage threshold for the promotion"));
+
+// Set the maximum number of targets to promote for a single indirect-call
+// callsite.
+static cl::opt<unsigned>
+    MaxNumPromotions("icp-max-prom", cl::init(2), cl::Hidden, cl::ZeroOrMore,
+                     cl::desc("Max number of promotions for a single indirect "
+                              "call callsite"));
+
+ICallPromotionAnalysis::ICallPromotionAnalysis() {
+  ValueDataArray = llvm::make_unique<InstrProfValueData[]>(MaxNumPromotions);
+}
+
+bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
+                                                   uint64_t TotalCount) {
+  if (Count < ICPCountThreshold)
+    return false;
+
+  unsigned Percentage = (Count * 100) / TotalCount;
+  return (Percentage >= ICPPercentThreshold);
+}
+
+// Indirect-call promotion heuristic. The direct targets are sorted based on
+// the count. Stop at the first target that is not promoted. Returns the
+// number of candidates deemed profitable.
+uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
+    const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) {
+  ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals);
+
+  DEBUG(dbgs() << " \nWork on callsite " << *Inst << " Num_targets: " << NumVals
+               << "\n");
+
+  uint32_t I = 0;
+  for (; I < MaxNumPromotions && I < NumVals; I++) {
+    uint64_t Count = ValueDataRef[I].Count;
+    assert(Count <= TotalCount);
+    uint64_t Target = ValueDataRef[I].Value;
+    DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
+                 << "  Target_func: " << Target << "\n");
+
+    if (!isPromotionProfitable(Count, TotalCount)) {
+      DEBUG(dbgs() << " Not promote: Cold target.\n");
+      return I;
+    }
+    TotalCount -= Count;
+  }
+  return I;
+}
+
+ArrayRef<InstrProfValueData>
+ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
+    const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount,
+    uint32_t &NumCandidates) {
+  bool Res =
+      getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions,
+                               ValueDataArray.get(), NumVals, TotalCount);
+  if (!Res) {
+    NumCandidates = 0;
+    return ArrayRef<InstrProfValueData>();
+  }
+  NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount);
+  return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals);
+}