From eae4742d81ef598dc2000312ad2471c4632bcb83 Mon Sep 17 00:00:00 2001
From: Bob Haarman <llvm@inglorion.net>
Date: Fri, 27 Jul 2018 05:40:29 +0000
Subject: [PATCH] [LTO] Don't internalize declarations

Summary:
Some links were failing with "Global is external, but doesn't have
external or weak linkage!" in ThinLTO builds with debug
information. This happened when we elide the body of a global that is
referenced by debug info. This results in a declaration, which we
would then internalize - but declarations cannot be internal. This
change avoids the problem by not internalizing these declarations.

Fixes PR38046.

Reviewers: pcc, tejohnson

Subscribers: mehdi_amini, aprantl, hiraditya, JDevlieghere, steven_wu, dexonsmith, llvm-commits

Differential Revision: https://reviews.llvm.org/D49777

llvm-svn: 338100
---
 llvm/lib/LTO/LTO.cpp         |  3 ++-
 llvm/test/LTO/X86/pr38046.ll | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/LTO/X86/pr38046.ll

diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 32b48ddfef7e..68d210cb7d73 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -872,7 +872,8 @@ Error LTO::runRegularLTO(AddStreamFn AddStream) {
       GlobalValue *GV =
           RegularLTO.CombinedModule->getNamedValue(R.second.IRName);
       // Ignore symbols defined in other partitions.
-      if (!GV || GV->hasLocalLinkage())
+      // Also skip declarations, which are not allowed to have internal linkage.
+      if (!GV || GV->hasLocalLinkage() || GV->isDeclaration())
         continue;
       GV->setUnnamedAddr(R.second.UnnamedAddr ? GlobalValue::UnnamedAddr::Global
                                               : GlobalValue::UnnamedAddr::None);
diff --git a/llvm/test/LTO/X86/pr38046.ll b/llvm/test/LTO/X86/pr38046.ll
new file mode 100644
index 000000000000..6743121b7156
--- /dev/null
+++ b/llvm/test/LTO/X86/pr38046.ll
@@ -0,0 +1,34 @@
+; RUN: opt -module-summary -o %t.o %s
+; RUN: llvm-lto2 run -save-temps -o %t.lto.o %t.o \
+; RUN:   -r=%t.o,foo,plx \
+; RUN:   -r=%t.o,get,pl
+; RUN: llvm-dis %t.lto.o.0.2.internalize.bc >/dev/null 2>%t.dis.stderr || true
+; RUN: FileCheck -allow-empty %s < %t.dis.stderr
+
+; CHECK-NOT: Global is external, but doesn't have external or weak linkage
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @foo() {
+  call void @llvm.dbg.value(metadata i32 ()* @get, metadata !7, metadata !DIExpression()), !dbg !DILocation(scope: !6)
+  ret i32 0
+}
+
+define i32 @get() {
+  ret i32 0
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1)
+!1 = !DIFile(filename: "t.cc", directory: "/tmp/t")
+!2 = !{i32 2, !"Dwarf Version", i32 4}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 1, !"ThinLTO", i32 0}
+!6 = distinct !DISubprogram(unit: !0)
+!7 = !DILocalVariable(name: "get", scope: !6)