[lld] r264790 - [LTO] Teach LTO about @llvm.used global.

[Davide Italiano via llvm-commits]

Author: davide
Date: Tue Mar 29 16:46:35 2016
New Revision: 264790

URL: http://llvm.org/viewvc/llvm-project?rev=264790&view=rev
Log:
[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.

Added:
    lld/trunk/test/ELF/lto/internalize-llvmused.ll
Modified:
    lld/trunk/ELF/LTO.cpp

Modified: lld/trunk/ELF/LTO.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/LTO.cpp?rev=264790&r1=264789&r2=264790&view=diff
==============================================================================
--- lld/trunk/ELF/LTO.cpp (original)
+++ lld/trunk/ELF/LTO.cpp Tue Mar 29 16:46:35 2016
@@ -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);
   }

Added: lld/trunk/test/ELF/lto/internalize-llvmused.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/lto/internalize-llvmused.ll?rev=264790&view=auto
==============================================================================
--- lld/trunk/test/ELF/lto/internalize-llvmused.ll (added)
+++ lld/trunk/test/ELF/lto/internalize-llvmused.ll Tue Mar 29 16:46:35 2016
@@ -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
+}
+
+ at llvm.used = appending global [1 x i8*] [ i8* bitcast (void ()* @f to i8*)]
+
+; Check that f is not internalized.
+; CHECK: define hidden void @f()