LTO: Export functions referenced by the CFI jump table.

If the LowerTypeTests pass decides to add a function to a jump
table for CFI, it will add its name to the set cfiFunctionDefs,
which among other things will cause the function to be renamed in
the ThinLTO backend.

One other thing that we must do with such functions is to not
internalize them, because the jump table in the full LTO object will
contain a reference to the actual function body in the ThinLTO object.

This patch handles that by ensuring that we export any functions
whose names appear in the cfiFunctionDefs set.

Fixes PR33831.

Differential Revision: https://reviews.llvm.org/D35605

llvm-svn: 308504

2 files changed, 38 insertions, 0 deletions

diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 19973946ac5..958151ad91b 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -1072,6 +1072,12 @@ Error LTO::runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache,
         ExportedGUIDs.insert(GUID);
     }
 
+    // Any functions referenced by the jump table in the regular LTO object must
+    // be exported.
+    for (auto &Def : ThinLTO.CombinedIndex.cfiFunctionDefs())
+      ExportedGUIDs.insert(
+          GlobalValue::getGUID(GlobalValue::dropLLVMManglingEscape(Def)));
+
     auto isExported = [&](StringRef ModuleIdentifier, GlobalValue::GUID GUID) {
       const auto &ExportList = ExportLists.find(ModuleIdentifier);
       return (ExportList != ExportLists.end() &&
diff --git a/llvm/test/LTO/Resolution/X86/export-jumptable.ll b/llvm/test/LTO/Resolution/X86/export-jumptable.ll
new file mode 100644
index 00000000000..1ab8c065014
--- /dev/null
+++ b/llvm/test/LTO/Resolution/X86/export-jumptable.ll
@@ -0,0 +1,32 @@
+; Test that we do not internalize functions that appear in the CFI jump table in
+; the full LTO object file; any such functions will be referenced by the jump
+; table.
+
+; RUN: opt -thinlto-bc -o %t %s
+; RUN: llvm-lto2 run -o %t2 -r %t,f1,p -r %t,f2,p -r %t,_start,px %t -save-temps
+; RUN: llvm-dis %t2.1.2.internalize.bc -o - | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK: define void @f1()
+define void @f1() !type !0 {
+  ret void
+}
+
+; CHECK: define internal void @f2()
+define void @f2() !type !1 {
+  ret void
+}
+
+define i1 @_start(i8* %p) {
+  %1 = call i1 @llvm.type.test(i8* %p, metadata !"typeid1")
+  call void @f1()
+  call void @f2()
+  ret i1 %1
+}
+
+declare i1 @llvm.type.test(i8*, metadata)
+
+!0 = !{i64 0, !"typeid1"}
+!1 = !{i64 0, !"typeid2"}