From: Mehdi Amini <mehdi.amini@apple.com>
Date: Thu, 5 May 2016 05:14:20 +0000 (+0000)
Subject: Revert "LTOCodeGenerator: turns linkonce(_odr) into weak_(odr) when present "MustPres... 
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=3556cc73fe6ec3152f21e3087310097834e32c52;p=llvm

Revert "LTOCodeGenerator: turns linkonce(_odr) into weak_(odr) when present "MustPreserve" set"

This reverts commit r267644. Turning linkonce_odr into weak_odr is
a sementic change on Darwin: because of
`llvm::canBeOmittedFromSymbolTable()` we may emit the symbol as
weak_def_can_be_hidden instead of weak_definition.

From: Mehdi Amini <mehdi.amini@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268606 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/LTO/LTOCodeGenerator.cpp b/lib/LTO/LTOCodeGenerator.cpp
index 712632761ea..30cff727513 100644
--- a/lib/LTO/LTOCodeGenerator.cpp
+++ b/lib/LTO/LTOCodeGenerator.cpp
@@ -348,62 +348,14 @@ std::unique_ptr<TargetMachine> LTOCodeGenerator::createTargetMachine() {
                                  RelocModel, CodeModel::Default, CGOptLevel));
 }
 
-// If a linkonce global is present in the MustPreserveSymbols, we need to make
-// sure we honor this. To force the compiler to not drop it, we turn its linkage
-// to the weak equivalent.
-static void
-preserveDiscardableGVs(Module &TheModule,
-                       function_ref<bool(const GlobalValue &)> mustPreserveGV) {
-  auto mayPreserveGlobal = [&](GlobalValue &GV) {
-    if (!GV.isDiscardableIfUnused() || GV.isDeclaration())
-      return;
-    if (!mustPreserveGV(GV))
-      return;
-    if (GV.hasAvailableExternallyLinkage() || GV.hasLocalLinkage())
-      report_fatal_error("The linker asked LTO to preserve a symbol with an"
-                         "unexpected linkage");
-    GV.setLinkage(GlobalValue::getWeakLinkage(GV.hasLinkOnceODRLinkage()));
-  };
-
-  for (auto &GV : TheModule)
-    mayPreserveGlobal(GV);
-  for (auto &GV : TheModule.globals())
-    mayPreserveGlobal(GV);
-  for (auto &GV : TheModule.aliases())
-    mayPreserveGlobal(GV);
-}
-
 void LTOCodeGenerator::applyScopeRestrictions() {
-  if (ScopeRestrictionsDone)
-    return;
-
-  // Declare a callback for the internalize pass that will ask for every
-  // candidate GlobalValue if it can be internalized or not.
-  SmallString<64> MangledName;
-  auto mustPreserveGV = [&](const GlobalValue &GV) -> bool {
-    // Unnamed globals can't be mangled, but they can't be preserved either.
-    if (!GV.hasName())
-      return false;
-
-    // Need to mangle the GV as the "MustPreserveSymbols" StringSet is filled
-    // with the linker supplied name, which on Darwin includes a leading
-    // underscore.
-    MangledName.clear();
-    MangledName.reserve(GV.getName().size() + 1);
-    Mangler::getNameWithPrefix(MangledName, GV.getName(),
-                               MergedModule->getDataLayout());
-    return MustPreserveSymbols.count(MangledName);
-  };
-
-  // Preserve linkonce value on linker request
-  preserveDiscardableGVs(*MergedModule, mustPreserveGV);
-
-  if (!ShouldInternalize)
+  if (ScopeRestrictionsDone || !ShouldInternalize)
     return;
 
   if (ShouldRestoreGlobalsLinkage) {
     // Record the linkage type of non-local symbols so they can be restored
-    // prior to module splitting.
+    // prior
+    // to module splitting.
     auto RecordLinkage = [&](const GlobalValue &GV) {
       if (!GV.hasAvailableExternallyLinkage() && !GV.hasLocalLinkage() &&
           GV.hasName())
@@ -421,7 +373,22 @@ void LTOCodeGenerator::applyScopeRestrictions() {
   // symbols referenced from asm
   UpdateCompilerUsed(*MergedModule, *TargetMach, AsmUndefinedRefs);
 
-  internalizeModule(*MergedModule, mustPreserveGV);
+  // Declare a callback for the internalize pass that will ask for every
+  // candidate GlobalValue if it can be internalized or not.
+  Mangler Mangler;
+  SmallString<64> MangledName;
+  auto MustPreserveGV = [&](const GlobalValue &GV) -> bool {
+    // Need to mangle the GV as the "MustPreserveSymbols" StringSet is filled
+    // with the linker supplied name, which on Darwin includes a leading
+    // underscore.
+    MangledName.clear();
+    MangledName.reserve(GV.getName().size() + 1);
+    Mangler::getNameWithPrefix(MangledName, GV.getName(),
+                               MergedModule->getDataLayout());
+    return MustPreserveSymbols.count(MangledName);
+  };
+
+  internalizeModule(*MergedModule, MustPreserveGV);
 
   ScopeRestrictionsDone = true;
 }
diff --git a/test/tools/lto/hide-linkonce-odr.ll b/test/tools/lto/hide-linkonce-odr.ll
index a2b0c6eb930..a1de96e8b33 100644
--- a/test/tools/lto/hide-linkonce-odr.ll
+++ b/test/tools/lto/hide-linkonce-odr.ll
@@ -1,11 +1,9 @@
 ; RUN: llvm-as %s -o %t.o
-; RUN: %ld64 -lto_library %llvmshlibdir/libLTO.dylib -dylib -arch x86_64 -macosx_version_min 10.10.0 -lSystem -o %t.dylib %t.o -save-temps  -undefined dynamic_lookup -exported_symbol _c -exported_symbol _b
+; RUN: %ld64 -lto_library %llvmshlibdir/libLTO.dylib -dylib -arch x86_64 -macosx_version_min 10.10.0 -lSystem -o %t.dylib %t.o -save-temps  -undefined dynamic_lookup
 
 ; RUN: llvm-dis %t.dylib.lto.opt.bc -o - | FileCheck --check-prefix=IR %s
-; check that @a is no longer a linkonce_odr definition
-; IR-NOT: define linkonce_odr void @a()
-; check that @b is turned into weak because it is exported
-; IR: define weak_odr void @b() #1 {
+; check that @a is still a linkonce_odr definition
+; IR: define linkonce_odr void @a()
 
 ; RUN: llvm-nm %t.dylib | FileCheck --check-prefix=NM %s
 ; check that the linker can hide @a but not @b