[LTO] Emit DebugLoc for dead function in optimization remarks

Currently, the dead functions information getting from optimizations remarks does not contain debug location, but knowing where these dead functions locate could be useful for debugging or for detecting dead code.

Cause in `LTO::addRegularLTO()` we use `BitcodeModule::getLazyModule()` to read the bitcode module, when we pass Function F to `ore::NV()`, F is not materialized, so `F->getSubprogram()` returns nullptr, and there is no debug location information of dead functions in optimizations remarks.

This patch call `F->materialize()` before we pass Function F to `ore::NV()`, then debug location information will be emitted for dead functions in optimization remarks.

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D109737

llvm/include/llvm/LTO/LTO.h

@@ -444,6 +444,9 @@ private:
   // Identify symbols exported dynamically, and that therefore could be
   // referenced by a shared library not visible to the linker.
   DenseSet<GlobalValue::GUID> DynamicExportSymbols;
+
+  // Diagnostic optimization remarks file
+  std::unique_ptr<ToolOutputFile> DiagnosticOutputFile;
 };
 
 /// The resolution for a symbol. The linker must provide a SymbolResolution for

llvm/lib/LTO/LTO.cpp

@@ -857,11 +857,15 @@ Error LTO::linkRegularLTO(RegularLTOState::AddedModule Mod,
   for (GlobalValue *GV : Mod.Keep) {
     if (LivenessFromIndex && !ThinLTO.CombinedIndex.isGUIDLive(GV->getGUID())) {
       if (Function *F = dyn_cast<Function>(GV)) {
+        if (DiagnosticOutputFile) {
+          if (Error Err = F->materialize())
+            return Err;
           OptimizationRemarkEmitter ORE(F, nullptr);
           ORE.emit(OptimizationRemark(DEBUG_TYPE, "deadfunction", F)
                    << ore::NV("Function", F)
                    << " not added to the combined module ");
         }
+      }
       continue;
     }
 
@@ -1049,6 +1053,7 @@ Error LTO::runRegularLTO(AddStreamFn AddStream) {
       Conf.RemarksHotnessThreshold);
   if (!DiagFileOrErr)
     return DiagFileOrErr.takeError();
+  DiagnosticOutputFile = std::move(*DiagFileOrErr);
 
   // Finalize linking of regular LTO modules containing summaries now that
   // we have computed liveness information.
@@ -1137,7 +1142,7 @@ Error LTO::runRegularLTO(AddStreamFn AddStream) {
       return Err;
   }
 
-  return finalizeOptimizationRemarks(std::move(*DiagFileOrErr));
+  return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
 }
 
 static const char *libcallRoutineNames[] = {

llvm/test/LTO/Resolution/X86/dead-strip-fulllto.ll

@@ -19,9 +19,11 @@
 
 ; REMARK:      Pass:            lto
 ; REMARK-NEXT: Name:            deadfunction
+; REMARK-NEXT: DebugLoc:        { File: test.c, Line: 4, Column: 0 }
 ; REMARK-NEXT: Function:        dead2
 ; REMARK-NEXT: Args:
 ; REMARK-NEXT:   - Function:        dead2
+; REMARK-NEXT:     DebugLoc:        { File: test.c, Line: 4, Column: 0 }
 ; REMARK-NEXT:   - String:          ' not added to the combined module '
 
 ; FULL-NOT: dead
@@ -48,9 +50,18 @@ define void @live2() {
   ret void
 }
 
-define void @dead2() {
+define void @dead2() !dbg !7 {
   ret void
 }
 
-!0 = !{i32 1, !"ThinLTO", i32 0}
-!llvm.module.flags = !{ !0 }
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, isOptimized: false, emissionKind: LineTablesOnly, enums: !2)
+!1 = !DIFile(filename: "test.c", directory: "/")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 2}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"ThinLTO", i32 0}
+!7 = distinct !DISubprogram(name: "dead2", scope: !1, file: !1, line: 4, type: !8, isLocal: false, isDefinition: true, scopeLine: 4, isOptimized: false, unit: !0, retainedNodes: !2)
+!8 = !DISubroutineType(types: !2)