Revert "[CFI] Remove LinkerSubsectionsViaSymbols."

This reverts commit r304582: breaks cfi-devirt :: anon-namespace.cpp on Darwin.

llvm-svn: 304626

1 files changed, 23 insertions, 12 deletions

diff --git a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
index eb6f05b653c..7bec50d9d25 100644
--- a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
+++ b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
@@ -235,6 +235,7 @@ class LowerTypeTestsModule {
   ModuleSummaryIndex *ExportSummary;
   const ModuleSummaryIndex *ImportSummary;
 
+  bool LinkerSubsectionsViaSymbols;
   Triple::ArchType Arch;
   Triple::OSType OS;
   Triple::ObjectFormatType ObjectFormat;
@@ -474,9 +475,13 @@ void LowerTypeTestsModule::allocateByteArrays() {
     // Create an alias instead of RAUW'ing the gep directly. On x86 this ensures
     // that the pc-relative displacement is folded into the lea instead of the
     // test instruction getting another displacement.
-    GlobalAlias *Alias = GlobalAlias::create(
-        Int8Ty, 0, GlobalValue::PrivateLinkage, "bits", GEP, &M);
-    BAI->ByteArray->replaceAllUsesWith(Alias);
+    if (LinkerSubsectionsViaSymbols) {
+      BAI->ByteArray->replaceAllUsesWith(GEP);
+    } else {
+      GlobalAlias *Alias = GlobalAlias::create(
+          Int8Ty, 0, GlobalValue::PrivateLinkage, "bits", GEP, &M);
+      BAI->ByteArray->replaceAllUsesWith(Alias);
+    }
     BAI->ByteArray->eraseFromParent();
   }
 
@@ -497,7 +502,7 @@ Value *LowerTypeTestsModule::createBitSetTest(IRBuilder<> &B,
     return createMaskedBitTest(B, TIL.InlineBits, BitOffset);
   } else {
     Constant *ByteArray = TIL.TheByteArray;
-    if (AvoidReuse && !ImportSummary) {
+    if (!LinkerSubsectionsViaSymbols && AvoidReuse && !ImportSummary) {
       // Each use of the byte array uses a different alias. This makes the
       // backend less likely to reuse previously computed byte array addresses,
       // improving the security of the CFI mechanism based on this pass.
@@ -675,13 +680,17 @@ void LowerTypeTestsModule::buildBitSetsFromGlobalVariables(
                                       ConstantInt::get(Int32Ty, I * 2)};
     Constant *CombinedGlobalElemPtr = ConstantExpr::getGetElementPtr(
         NewInit->getType(), CombinedGlobal, CombinedGlobalIdxs);
-    assert(GV->getType()->getAddressSpace() == 0);
-    GlobalAlias *GAlias =
-        GlobalAlias::create(NewTy->getElementType(I * 2), 0, GV->getLinkage(),
-                            "", CombinedGlobalElemPtr, &M);
-    GAlias->setVisibility(GV->getVisibility());
-    GAlias->takeName(GV);
-    GV->replaceAllUsesWith(GAlias);
+    if (LinkerSubsectionsViaSymbols) {
+      GV->replaceAllUsesWith(CombinedGlobalElemPtr);
+    } else {
+      assert(GV->getType()->getAddressSpace() == 0);
+      GlobalAlias *GAlias = GlobalAlias::create(NewTy->getElementType(I * 2), 0,
+                                                GV->getLinkage(), "",
+                                                CombinedGlobalElemPtr, &M);
+      GAlias->setVisibility(GV->getVisibility());
+      GAlias->takeName(GV);
+      GV->replaceAllUsesWith(GAlias);
+    }
     GV->eraseFromParent();
   }
 }
@@ -1157,7 +1166,8 @@ void LowerTypeTestsModule::buildBitSetsFromFunctionsNative(
             ArrayRef<Constant *>{ConstantInt::get(IntPtrTy, 0),
                                  ConstantInt::get(IntPtrTy, I)}),
         F->getType());
-    if (F->isDeclarationForLinker()) {
+    if (LinkerSubsectionsViaSymbols || F->isDeclarationForLinker()) {
+
       if (F->isWeakForLinker())
         replaceWeakDeclarationWithJumpTablePtr(F, CombinedGlobalElemPtr);
       else
@@ -1292,6 +1302,7 @@ LowerTypeTestsModule::LowerTypeTestsModule(
     : M(M), ExportSummary(ExportSummary), ImportSummary(ImportSummary) {
   assert(!(ExportSummary && ImportSummary));
   Triple TargetTriple(M.getTargetTriple());
+  LinkerSubsectionsViaSymbols = TargetTriple.isMacOSX();
   Arch = TargetTriple.getArch();
   OS = TargetTriple.getOS();
   ObjectFormat = TargetTriple.getObjectFormat();