[LTO] Teach LTO about @llvm.used global.

If a symbol appears in @llvm.used, the linker is forced to treat
the symbol as there's a reference to it.

llvm-svn: 264790

diff --git a/lld/ELF/LTO.cpp b/lld/ELF/LTO.cpp
index 191ec72..9a24115 100644 (file)
--- a/lld/ELF/LTO.cpp
+++ b/lld/ELF/LTO.cpp
@@ -21,6 +21,7 @@
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Transforms/IPO.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
 
 using namespace llvm;
@@ -76,6 +77,10 @@ void BitcodeCompiler::add(BitcodeFile &F) {
   unsigned BodyIndex = 0;
   ArrayRef<SymbolBody *> Bodies = F.getSymbols();
 
+  Module &M = Obj->getModule();
+  SmallPtrSet<GlobalValue *, 8> Used;
+  collectUsedGlobalVariables(M, Used, /* CompilerUsed */ false);
+
   for (const BasicSymbolRef &Sym : Obj->symbols()) {
     GlobalValue *GV = Obj->getSymbolGV(Sym.getRawDataRefImpl());
     assert(GV);
@@ -108,7 +113,8 @@ void BitcodeCompiler::add(BitcodeFile &F) {
     // For now, let's be conservative and just never internalize
     // symbols when creating a shared library.
     if (!Config->Shared && !Config->ExportDynamic && !B->isUsedInRegularObj())
-      InternalizedSyms.insert(GV->getName());
+      if (!Used.count(GV))
+        InternalizedSyms.insert(GV->getName());
 
     Keep.push_back(GV);
   }

diff --git a/lld/test/ELF/lto/internalize-llvmused.ll b/lld/test/ELF/lto/internalize-llvmused.ll
new file mode 100644 (file)
index 0000000..46c90a6
--- /dev/null
+++ b/lld/test/ELF/lto/internalize-llvmused.ll
@@ -0,0 +1,20 @@
+; REQUIRES: x86
+; RUN: llvm-as %s -o %t.o
+; RUN: ld.lld -m elf_x86_64 %t.o -o %t2 -save-temps
+; RUN: llvm-dis < %t2.lto.bc | FileCheck %s
+
+target triple = "x86_64-unknown-linux-gnu"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @_start() {
+  ret void
+}
+
+define hidden void @f() {
+  ret void
+}
+
+@llvm.used = appending global [1 x i8*] [ i8* bitcast (void ()* @f to i8*)]
+
+; Check that f is not internalized.
+; CHECK: define hidden void @f()