CodeGen, Target: Move Mach-O-specific symbol name logic to Mach-O lowering.

A profile of an LTO link of Chrome revealed that we were spending some
~30-50% of execution time in the function Constant::getRelocationInfo(),
which is called from TargetLoweringObjectFile::getKindForGlobal() and in turn
from TargetMachine::getNameWithPrefix().

It turns out that we only need the result of getKindForGlobal() when
targeting Mach-O, so this change moves the relevant part of the logic to
TargetLoweringObjectFileMachO.

NFCI.

Differential Revision: http://reviews.llvm.org/D14168

llvm-svn: 252014

1 files changed, 28 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 0f46571..372ac40 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -24,6 +24,7 @@
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/Mangler.h"
 #include "llvm/IR/Module.h"
+#include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCSectionCOFF.h"
@@ -763,6 +764,29 @@ const MCExpr *TargetLoweringObjectFileMachO::getIndirectSymViaGOTPCRel(
   return MCBinaryExpr::createSub(LHS, RHS, Ctx);
 }
 
+static bool canUsePrivateLabel(const MCAsmInfo &AsmInfo,
+                               const MCSection &Section) {
+  if (!AsmInfo.isSectionAtomizableBySymbols(Section))
+    return true;
+
+  // If it is not dead stripped, it is safe to use private labels.
+  const MCSectionMachO &SMO = cast<MCSectionMachO>(Section);
+  if (SMO.hasAttribute(MachO::S_ATTR_NO_DEAD_STRIP))
+    return true;
+
+  return false;
+}
+
+void TargetLoweringObjectFileMachO::getNameWithPrefix(
+    SmallVectorImpl<char> &OutName, const GlobalValue *GV, Mangler &Mang,
+    const TargetMachine &TM) const {
+  SectionKind GVKind = TargetLoweringObjectFile::getKindForGlobal(GV, TM);
+  const MCSection *TheSection = SectionForGlobal(GV, GVKind, Mang, TM);
+  bool CannotUsePrivateLabel =
+      !canUsePrivateLabel(*TM.getMCAsmInfo(), *TheSection);
+  Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
+}
+
 //===----------------------------------------------------------------------===//
 //                                  COFF
 //===----------------------------------------------------------------------===//
@@ -918,7 +942,7 @@ MCSection *TargetLoweringObjectFileCOFF::SelectSectionForGlobal(
                                          COMDATSymName, Selection);
     } else {
       SmallString<256> TmpData;
-      getNameWithPrefix(TmpData, GV, /*CannotUsePrivateLabel=*/true, Mang, TM);
+      Mang.getNameWithPrefix(TmpData, GV, /*CannotUsePrivateLabel=*/true);
       return getContext().getCOFFSection(Name, Characteristics, Kind, TmpData,
                                          Selection);
     }
@@ -943,8 +967,9 @@ MCSection *TargetLoweringObjectFileCOFF::SelectSectionForGlobal(
 }
 
 void TargetLoweringObjectFileCOFF::getNameWithPrefix(
-    SmallVectorImpl<char> &OutName, const GlobalValue *GV,
-    bool CannotUsePrivateLabel, Mangler &Mang, const TargetMachine &TM) const {
+    SmallVectorImpl<char> &OutName, const GlobalValue *GV, Mangler &Mang,
+    const TargetMachine &TM) const {
+  bool CannotUsePrivateLabel = false;
   if (GV->hasPrivateLinkage() &&
       ((isa<Function>(GV) && TM.getFunctionSections()) ||
        (isa<GlobalVariable>(GV) && TM.getDataSections())))