Add support for generating a call graph profile from Branch Frequency Info.

=== Generating the CG Profile ===

The CGProfile module pass simply gets the block profile count for each BB and scans for call instructions.  For each call instruction it adds an edge from the current function to the called function with the current BB block profile count as the weight.

After scanning all the functions, it generates an appending module flag containing the data. The format looks like:
```
!llvm.module.flags = !{!0}

!0 = !{i32 5, !"CG Profile", !1}
!1 = !{!2, !3, !4} ; List of edges
!2 = !{void ()* @a, void ()* @b, i64 32} ; Edge from a to b with a weight of 32
!3 = !{void (i1)* @freq, void ()* @a, i64 11}
!4 = !{void (i1)* @freq, void ()* @b, i64 20}
```

Differential Revision: https://reviews.llvm.org/D48105

llvm-svn: 335794

1 files changed, 100 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/CGProfile.cpp b/llvm/lib/Transforms/Instrumentation/CGProfile.cpp
new file mode 100644
index 00000000000..8a5ac2b47fa
--- /dev/null
+++ b/llvm/lib/Transforms/Instrumentation/CGProfile.cpp
@@ -0,0 +1,100 @@
+//===-- CGProfile.cpp -----------------------------------------------------===//
+//
+//                      The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Instrumentation/CGProfile.h"
+
+#include "llvm/ADT/MapVector.h"
+#include "llvm/Analysis/BlockFrequencyInfo.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/CallSite.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/MDBuilder.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/ProfileData/InstrProf.h"
+#include "llvm/Transforms/Instrumentation.h"
+
+#include <array>
+
+using namespace llvm;
+
+PreservedAnalyses CGProfilePass::run(Module &M, ModuleAnalysisManager &MAM) {
+  MapVector<std::pair<Function *, Function *>, uint64_t> Counts;
+  FunctionAnalysisManager &FAM =
+      MAM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
+  InstrProfSymtab Symtab;
+  auto UpdateCounts = [&](TargetTransformInfo &TTI, Function *F,
+                          Function *CalledF, uint64_t NewCount) {
+    if (!CalledF || !TTI.isLoweredToCall(CalledF))
+      return;
+    uint64_t &Count = Counts[std::make_pair(F, CalledF)];
+    Count = SaturatingAdd(Count, NewCount);
+  };
+  // Ignore error here.  Indirect calls are ignored if this fails.
+  (bool)Symtab.create(M);
+  for (auto &F : M) {
+    if (F.isDeclaration())
+      continue;
+    auto &BFI = FAM.getResult<BlockFrequencyAnalysis>(F);
+    if (BFI.getEntryFreq() == 0)
+      continue;
+    TargetTransformInfo &TTI = FAM.getResult<TargetIRAnalysis>(F);
+    for (auto &BB : F) {
+      Optional<uint64_t> BBCount = BFI.getBlockProfileCount(&BB);
+      if (!BBCount)
+        continue;
+      for (auto &I : BB) {
+        CallSite CS(&I);
+        if (!CS)
+          continue;
+        if (CS.isIndirectCall()) {
+          InstrProfValueData ValueData[8];
+          uint32_t ActualNumValueData;
+          uint64_t TotalC;
+          if (!getValueProfDataFromInst(*CS.getInstruction(),
+                                        IPVK_IndirectCallTarget, 8, ValueData,
+                                        ActualNumValueData, TotalC))
+            continue;
+          for (const auto &VD :
+               ArrayRef<InstrProfValueData>(ValueData, ActualNumValueData)) {
+            UpdateCounts(TTI, &F, Symtab.getFunction(VD.Value), VD.Count);
+          }
+          continue;
+        }
+        UpdateCounts(TTI, &F, CS.getCalledFunction(), *BBCount);
+      }
+    }
+  }
+
+  addModuleFlags(M, Counts);
+
+  return PreservedAnalyses::all();
+}
+
+void CGProfilePass::addModuleFlags(
+    Module &M,
+    MapVector<std::pair<Function *, Function *>, uint64_t> &Counts) const {
+  if (Counts.empty())
+    return;
+
+  LLVMContext &Context = M.getContext();
+  MDBuilder MDB(Context);
+  std::vector<Metadata *> Nodes;
+
+  for (auto E : Counts) {
+    SmallVector<Metadata *, 3> Vals;
+    Vals.push_back(ValueAsMetadata::get(E.first.first));
+    Vals.push_back(ValueAsMetadata::get(E.first.second));
+    Vals.push_back(MDB.createConstant(
+        ConstantInt::get(Type::getInt64Ty(Context), E.second)));
+    Nodes.push_back(MDNode::get(Context, Vals));
+  }
+
+  M.addModuleFlag(Module::Append, "CG Profile", MDNode::get(Context, Nodes));
+}