Respect llvm.used in Internalize.

The language reference says that:

"If a symbol appears in the @llvm.used list, then the compiler,
assembler, and linker are required to treat the symbol as if there is
a reference to the symbol that it cannot see"

Since even the linker cannot see the reference, we must assume that
the reference can be using the symbol table. For example, a user can add
__attribute__((used)) to a debug helper function like dump and use it from
a debugger.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187103 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 18 insertions, 0 deletions

diff --git a/lib/Transforms/Utils/ModuleUtils.cpp b/lib/Transforms/Utils/ModuleUtils.cpp
index d090b48721..ff6e6f9c60 100644
--- a/lib/Transforms/Utils/ModuleUtils.cpp
+++ b/lib/Transforms/Utils/ModuleUtils.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Utils/ModuleUtils.h"
+#include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
@@ -62,3 +63,20 @@ void llvm::appendToGlobalCtors(Module &M, Function *F, int Priority) {
 void llvm::appendToGlobalDtors(Module &M, Function *F, int Priority) {
   appendToGlobalArray("llvm.global_dtors", M, F, Priority);
 }
+
+GlobalVariable *
+llvm::collectUsedGlobalVariables(Module &M, SmallPtrSet<GlobalValue *, 8> &Set,
+                                 bool CompilerUsed) {
+  const char *Name = CompilerUsed ? "llvm.compiler.used" : "llvm.used";
+  GlobalVariable *GV = M.getGlobalVariable(Name);
+  if (!GV || !GV->hasInitializer())
+    return GV;
+
+  const ConstantArray *Init = cast<ConstantArray>(GV->getInitializer());
+  for (unsigned I = 0, E = Init->getNumOperands(); I != E; ++I) {
+    Value *Op = Init->getOperand(I);
+    GlobalValue *G = cast<GlobalValue>(Op->stripPointerCastsNoFollowAliases());
+    Set.insert(G);
+  }
+  return GV;
+}