7 files changed, 22 insertions, 23 deletions
diff --git a/lld/test/ELF/lto/asmundef.ll b/lld/test/ELF/lto/asmundef.ll
index 1c87cd01fad..d03a5e38721 100644
--- a/lld/test/ELF/lto/asmundef.ll
+++ b/lld/test/ELF/lto/asmundef.ll
@@ -20,6 +20,5 @@ define void @_start() {
   ret void
 }
 
-; CHECK: @llvm.compiler.used = appending global [1 x i8*] [i8* bitcast (void ()* @foo to i8*)], section "llvm.metadata"
-; CHECK: define internal void @foo
+; CHECK: define void @foo
 
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 9782c898bf5..1bc0d7361d4 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -415,7 +415,8 @@ void LTO::addSymbolToGlobalRes(const InputFile::Symbol &Sym,
   // Flag as visible outside of ThinLTO if visible from a regular object or
   // if this is a reference in the regular LTO partition.
   GlobalRes.VisibleOutsideThinLTO |=
-      (Res.VisibleToRegularObj || (Partition == GlobalResolution::RegularLTO));
+      (Res.VisibleToRegularObj || Sym.isUsed() ||
+       Partition == GlobalResolution::RegularLTO);
 }
 
 static void writeToResolutionFile(raw_ostream &OS, InputFile *Input,
diff --git a/llvm/lib/LTO/LTOBackend.cpp b/llvm/lib/LTO/LTOBackend.cpp
index 4bd251f727a..30447c528af 100644
--- a/llvm/lib/LTO/LTOBackend.cpp
+++ b/llvm/lib/LTO/LTOBackend.cpp
@@ -25,7 +25,6 @@
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/Verifier.h"
 #include "llvm/LTO/LTO.h"
-#include "llvm/LTO/legacy/UpdateCompilerUsed.h"
 #include "llvm/MC/SubtargetFeature.h"
 #include "llvm/Object/ModuleSymbolTable.h"
 #include "llvm/Passes/PassBuilder.h"
@@ -353,19 +352,6 @@ finalizeOptimizationRemarks(std::unique_ptr<tool_output_file> DiagOutputFile) {
   DiagOutputFile->os().flush();
 }
 
-static void handleAsmUndefinedRefs(Module &Mod, TargetMachine &TM) {
-  // Collect the list of undefined symbols used in asm and update
-  // llvm.compiler.used to prevent optimization to drop these from the output.
-  StringSet<> AsmUndefinedRefs;
-  ModuleSymbolTable::CollectAsmSymbols(
-      Mod,
-      [&AsmUndefinedRefs](StringRef Name, object::BasicSymbolRef::Flags Flags) {
-        if (Flags & object::BasicSymbolRef::SF_Undefined)
-          AsmUndefinedRefs.insert(Name);
-      });
-  updateCompilerUsed(Mod, TM, AsmUndefinedRefs);
-}
-
 Error lto::backend(Config &C, AddStreamFn AddStream,
                    unsigned ParallelCodeGenParallelismLevel,
                    std::unique_ptr<Module> Mod,
@@ -377,8 +363,6 @@ Error lto::backend(Config &C, AddStreamFn AddStream,
   std::unique_ptr<TargetMachine> TM =
       createTargetMachine(C, Mod->getTargetTriple(), *TOrErr);
 
-  handleAsmUndefinedRefs(*Mod, *TM);
-
   // Setup optimization remarks.
   auto DiagFileOrErr = lto::setupOptimizationRemarks(
       Mod->getContext(), C.RemarksFilename, C.RemarksWithHotness);
@@ -416,8 +400,6 @@ Error lto::thinBackend(Config &Conf, unsigned Task, AddStreamFn AddStream,
   std::unique_ptr<TargetMachine> TM =
       createTargetMachine(Conf, Mod.getTargetTriple(), *TOrErr);
 
-  handleAsmUndefinedRefs(Mod, *TM);
-
   if (Conf.CodeGenOnly) {
     codegen(Conf, TM.get(), AddStream, Task, Mod);
     return Error::success();
diff --git a/llvm/lib/Object/IRSymtab.cpp b/llvm/lib/Object/IRSymtab.cpp
index 367b1e8fb63..5f0837882d6 100644
--- a/llvm/lib/Object/IRSymtab.cpp
+++ b/llvm/lib/Object/IRSymtab.cpp
@@ -163,6 +163,9 @@ Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
   Sym.ComdatIndex = -1;
   auto *GV = Msym.dyn_cast<GlobalValue *>();
   if (!GV) {
+    // Undefined module asm symbols act as GC roots and are implicitly used.
+    if (Flags & object::BasicSymbolRef::SF_Undefined)
+      Sym.Flags |= 1 << storage::Symbol::FB_used;
     setStr(Sym.IRName, "");
     return Error::success();
   }
diff --git a/llvm/test/LTO/Resolution/X86/Inputs/mod-asm-used.ll b/llvm/test/LTO/Resolution/X86/Inputs/mod-asm-used.ll
new file mode 100644
index 00000000000..3b1988bb54d
--- /dev/null
+++ b/llvm/test/LTO/Resolution/X86/Inputs/mod-asm-used.ll
@@ -0,0 +1,4 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@foo = global i32 1, align 4
diff --git a/llvm/test/LTO/Resolution/X86/mod-asm-used.ll b/llvm/test/LTO/Resolution/X86/mod-asm-used.ll
new file mode 100644
index 00000000000..01befca84d0
--- /dev/null
+++ b/llvm/test/LTO/Resolution/X86/mod-asm-used.ll
@@ -0,0 +1,10 @@
+; RUN: opt -module-summary -o %t.bc %s
+; RUN: opt -module-summary -o %t2.bc %S/Inputs/mod-asm-used.ll
+; RUN: llvm-lto2 run %t.bc -r %t.bc,foo,l %t2.bc -r %t2.bc,foo,pl -o %t3
+; RUN: llvm-nm %t3.1 | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK: D foo
+module asm ".quad foo"
diff --git a/llvm/test/tools/gold/X86/asm_undefined2.ll b/llvm/test/tools/gold/X86/asm_undefined2.ll
index 6cb7a1cf3d0..a170f45a55a 100644
--- a/llvm/test/tools/gold/X86/asm_undefined2.ll
+++ b/llvm/test/tools/gold/X86/asm_undefined2.ll
@@ -11,8 +11,8 @@
 ; RUN:     --plugin-opt=thinlto -o %t2 %t.o
 ; RUN: llvm-dis < %t.o.5.precodegen.bc | FileCheck %s
 
-; Check that foo is properly appended to llvm.compiler.used
-; CHECK: @llvm.compiler.used = appending global [1 x i8*] [i8* bitcast (void ()* @foo to i8*)], section "llvm.metadata"
+; Check that foo is not internalized
+; CHECK: define void @foo
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"