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, 47 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index df8aecd7cf4..24ff42a34ff 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -91,6 +91,12 @@ static void GetObjCImageInfo(Module &M, unsigned &Version, unsigned &Flags,
 //                                  ELF
 //===----------------------------------------------------------------------===//
 
+void TargetLoweringObjectFileELF::Initialize(MCContext &Ctx,
+                                             const TargetMachine &TgtM) {
+  TargetLoweringObjectFile::Initialize(Ctx, TgtM);
+  TM = &TgtM;
+}
+
 void TargetLoweringObjectFileELF::emitModuleMetadata(MCStreamer &Streamer,
                                                      Module &M) const {
   auto &C = getContext();
@@ -116,15 +122,49 @@ void TargetLoweringObjectFileELF::emitModuleMetadata(MCStreamer &Streamer,
   StringRef Section;
 
   GetObjCImageInfo(M, Version, Flags, Section);
-  if (Section.empty())
+  if (!Section.empty()) {
+    auto *S = C.getELFSection(Section, ELF::SHT_PROGBITS, ELF::SHF_ALLOC);
+    Streamer.SwitchSection(S);
+    Streamer.EmitLabel(C.getOrCreateSymbol(StringRef("OBJC_IMAGE_INFO")));
+    Streamer.EmitIntValue(Version, 4);
+    Streamer.EmitIntValue(Flags, 4);
+    Streamer.AddBlankLine();
+  }
+
+  SmallVector<Module::ModuleFlagEntry, 8> ModuleFlags;
+  M.getModuleFlagsMetadata(ModuleFlags);
+
+  MDNode *CFGProfile = nullptr;
+
+  for (const auto &MFE : ModuleFlags) {
+    StringRef Key = MFE.Key->getString();
+    if (Key == "CG Profile") {
+      CFGProfile = cast<MDNode>(MFE.Val);
+      break;
+    }
+  }
+
+  if (!CFGProfile)
     return;
 
-  auto *S = C.getELFSection(Section, ELF::SHT_PROGBITS, ELF::SHF_ALLOC);
-  Streamer.SwitchSection(S);
-  Streamer.EmitLabel(C.getOrCreateSymbol(StringRef("OBJC_IMAGE_INFO")));
-  Streamer.EmitIntValue(Version, 4);
-  Streamer.EmitIntValue(Flags, 4);
-  Streamer.AddBlankLine();
+  auto GetSym = [this](const MDOperand &MDO) {
+    auto V = cast<ValueAsMetadata>(MDO);
+    const Function *F = cast<Function>(V->getValue());
+    return TM->getSymbol(F);
+  };
+
+  for (const auto &Edge : CFGProfile->operands()) {
+    MDNode *E = cast<MDNode>(Edge);
+    const MCSymbol *From = GetSym(E->getOperand(0));
+    const MCSymbol *To = GetSym(E->getOperand(1));
+    uint64_t Count = cast<ConstantAsMetadata>(E->getOperand(2))
+                         ->getValue()
+                         ->getUniqueInteger()
+                         .getZExtValue();
+    Streamer.emitCGProfileEntry(
+        MCSymbolRefExpr::create(From, MCSymbolRefExpr::VK_None, C),
+        MCSymbolRefExpr::create(To, MCSymbolRefExpr::VK_None, C), Count);
+  }
 }
 
 MCSymbol *TargetLoweringObjectFileELF::getCFIPersonalitySymbol(