Add prefix based function layout when profile is available.

Summary: If a function is hot, put it in text.hot section.

Reviewers: davidxl

Subscribers: eraman, mcrosier, llvm-commits

Differential Revision: http://reviews.llvm.org/D17460

llvm-svn: 261582

2 files changed, 37 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 81b429a8d11..624eaec73b4 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -34,6 +34,7 @@
 #include "llvm/MC/MCSymbolELF.h"
 #include "llvm/MC/MCValue.h"
 #include "llvm/ProfileData/InstrProf.h"
+#include "llvm/ProfileData/ProfileCommon.h"
 #include "llvm/Support/COFF.h"
 #include "llvm/Support/Dwarf.h"
 #include "llvm/Support/ELF.h"
@@ -244,6 +245,11 @@ static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
   return ".data.rel.ro";
 }
 
+static cl::opt<bool> GroupFunctionsByHotness(
+    "group-functions-by-hotness",
+    llvm::cl::desc("Partition hot/cold functions by sections prefix"),
+    cl::init(false));
+
 static MCSectionELF *
 selectELFSectionForGlobal(MCContext &Ctx, const GlobalValue *GV,
                           SectionKind Kind, Mangler &Mang,
@@ -294,6 +300,16 @@ selectELFSectionForGlobal(MCContext &Ctx, const GlobalValue *GV,
     Name = getSectionPrefixForGlobal(Kind);
   }
 
+  if (GroupFunctionsByHotness) {
+    if (const Function *F = dyn_cast<Function>(GV)) {
+      if (ProfileSummary::isFunctionHot(F)) {
+        Name += getHotSectionPrefix();
+      } else if (ProfileSummary::isFunctionUnlikely(F)) {
+        Name += getUnlikelySectionPrefix();
+      }
+    }
+  }
+
   if (EmitUniqueSection && UniqueSectionNames) {
     Name.push_back('.');
     TM.getNameWithPrefix(Name, GV, Mang, true);
diff --git a/llvm/lib/ProfileData/ProfileSummary.cpp b/llvm/lib/ProfileData/ProfileSummary.cpp
index 0e2c43e5e91..0363fbfe42d 100644
--- a/llvm/lib/ProfileData/ProfileSummary.cpp
+++ b/llvm/lib/ProfileData/ProfileSummary.cpp
@@ -11,6 +11,9 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Module.h"
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/ProfileData/ProfileCommon.h"
 #include "llvm/ProfileData/SampleProf.h"
@@ -75,6 +78,24 @@ void ProfileSummary::computeDetailedSummary() {
   }
 }
 
+// Returns true if the function is a hot function.
+bool ProfileSummary::isFunctionHot(const Function *F) {
+  // FIXME: update when summary data is stored in module's metadata.
+  return false;
+}
+
+// Returns true if the function is a cold function.
+bool ProfileSummary::isFunctionUnlikely(const Function *F) {
+  if (F->hasFnAttribute(Attribute::Cold)) {
+    return true;
+  }
+  if (!F->getEntryCount()) {
+    return false;
+  }
+  // FIXME: update when summary data is stored in module's metadata.
+  return (*F->getEntryCount()) == 0;
+}
+
 InstrProfSummary::InstrProfSummary(const IndexedInstrProf::Summary &S)
     : ProfileSummary(), MaxInternalBlockCount(S.get(
                             IndexedInstrProf::Summary::MaxInternalBlockCount)),