[CodeView][DebugInfo] Update the code for removing template arguments from the display name of a codeview function id.

[akhuang]

Summary

Previously the code split the string at the first '<', which
incorrectly truncated names like operator<.

[rnk]

lgtm

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

388–389

I had to go remind myself why we don't do this in the frontend. The reason is that we put the template arguments in the S_GPROC32 symbol records, but we don't put them in the LF_FUNC_ID records. Can you update this comment to explain why we have to throw away the template arguments here? If we really wanted this to be super clean, we could change DISubprogram to split the name into the basename and the template argument list string, but that seems unnecessary.

[akhuang]

Add to comment

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

TypeIndex CodeViewDebug::getScopeIndex(const DIScope *Scope) {
 
   // Build the fully qualified name of the scope.
   std::string ScopeName = getFullyQualifiedName(Scope);
   StringIdRecord SID(TypeIndex(), ScopeName);
   auto TI = TypeTable.writeLeafType(SID);
   return recordTypeIndexForDINode(Scope, TI);
 }
 
+static StringRef removeTemplateArgs(StringRef Name) {
+  // Remove template args from the display name. Assume that the template args
+  // are the last thing in the name.
+  if (Name.empty() || Name.back() != '>')
+    return Name;
+
+  int openBrackets = 0;
+  for (size_t i = Name.size() - 1; i >= 0; --i) {
+    if (Name[i] == '>')
+      ++openBrackets;
+    else if (Name[i] == '<') {
+      --openBrackets;
+      if (openBrackets == 0)
+        return Name.substr(0, i);
+    }
+  }
+  return Name;
+}
+
 TypeIndex CodeViewDebug::getFuncIdForSubprogram(const DISubprogram *SP) {
   assert(SP);
 
   // Check if we've already translated this subprogram.
   auto I = TypeIndices.find({SP, nullptr});
   if (I != TypeIndices.end())
     return I->second;
 
   // The display name includes function template arguments. Drop them to match
   // MSVC.
-  StringRef DisplayName = SP->getName().split('<').first;
+  StringRef DisplayName = removeTemplateArgs(SP->getName());
 
   const DIScope *Scope = SP->getScope();
   TypeIndex TI;
   if (const auto *Class = dyn_cast_or_null<DICompositeType>(Scope)) {
     // If the scope is a DICompositeType, then this must be a method. Member
     // function types take some special handling, and require access to the
     // subprogram.
     TypeIndex ClassType = getTypeIndex(Class);

llvm/test/DebugInfo/COFF/cpp-mangling.ll

 ; RUN: llc -mcpu=core2 -mtriple=i686-pc-win32 -o - -O0 -filetype=obj < %s \
 ; RUN:   | llvm-readobj --codeview - | FileCheck %s
 
 ; C++ source to regenerate:
 ; namespace foo {
 ; int bar(int x) { return x * 2; }
 ; }
 ; template <typename T, int (*)(int)>
 ; void fn_tmpl() {}
 ; template void fn_tmpl<int, foo::bar>();
+; struct S { void operator<<(int i) {} };
 ; void f() {
 ;   fn_tmpl<int, foo::bar>();
+;   S s;
+;   s << 3;
 ; }
 
 ; CHECK:        {{.*}}Proc{{.*}}Sym {
 ; CHECK:         FunctionType: bar ({{.*}})
 ; CHECK:         DisplayName: foo::bar{{$}}
 ; CHECK-NEXT:    LinkageName: ?bar@foo@@YAHH@Z
 
 ; CHECK:        {{.*}}Proc{{.*}}Sym {
+; CHECK:         FunctionType: operator<< ({{.*}})
+; CHECK:         DisplayName: S::operator<<
+; CHECK-NEXT:    LinkageName: ??6S@@QAEXH@Z
+
+; CHECK:        {{.*}}Proc{{.*}}Sym {
 ; CHECK:         FunctionType: fn_tmpl ({{.*}})
 ; CHECK:         DisplayName: foo::fn_tmpl<int,&foo::bar>
 ; CHECK-NEXT:    LinkageName: ??$fn_tmpl@H$1?bar@foo@@YAHH@Z@foo@@YAXXZ
 
 ; ModuleID = 't.cpp'
 source_filename = "t.cpp"
 target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
 target triple = "i386-pc-windows-msvc19.0.23918"
 
+%struct.S = type { i8 }
+
 $"\01??$fn_tmpl@H$1?bar@foo@@YAHH@Z@foo@@YAXXZ" = comdat any
 
+$"??6S@@QAEXH@Z" = comdat any
+
 ; Function Attrs: nounwind
 define i32 @"\01?bar@foo@@YAHH@Z"(i32 %x) #0 !dbg !6 {
 entry:
   %x.addr = alloca i32, align 4
   store i32 %x, i32* %x.addr, align 4
   call void @llvm.dbg.declare(metadata i32* %x.addr, metadata !11, metadata !12), !dbg !13
   %0 = load i32, i32* %x.addr, align 4, !dbg !14
   %mul = mul nsw i32 %0, 2, !dbg !15
   ret i32 %mul, !dbg !16
 }
 
 ; Function Attrs: nounwind readnone
 declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
 
 ; Function Attrs: nounwind
 define weak_odr void @"\01??$fn_tmpl@H$1?bar@foo@@YAHH@Z@foo@@YAXXZ"() #0 comdat !dbg !17 {
 entry:
   ret void, !dbg !24
 }
 
+; Function Attrs: nounwind
+define linkonce_odr void @"??6S@@QAEXH@Z"(%struct.S* nonnull dereferenceable(1) %this, i32 %i) #0 !dbg !31 {
+entry:
+  %i.addr = alloca i32, align 4
+  %this.addr = alloca %struct.S*, align 4
+  store i32 %i, i32* %i.addr, align 4
+  store %struct.S* %this, %struct.S** %this.addr, align 4
+  %this1 = load %struct.S*, %struct.S** %this.addr, align 4
+  ret void, !dbg !32
+}
+
 attributes #0 = { nounwind "disable-tail-calls"="false" "less-precise-fpmad"="false" "frame-pointer"="all" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="pentium4" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
 attributes #1 = { nounwind readnone }
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!3, !4}
 !llvm.ident = !{!5}
 
 !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 3.9.0 ", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)

 !17 = distinct !DISubprogram(name: "fn_tmpl<int,&foo::bar>", linkageName: "\01??$fn_tmpl@H$1?bar@foo@@YAHH@Z@foo@@YAXXZ", scope: !7, file: !1, line: 4, type: !18, isLocal: false, isDefinition: true, scopeLine: 4, flags: DIFlagPrototyped, isOptimized: false, unit: !0, templateParams: !20, retainedNodes: !2)
 !18 = !DISubroutineType(types: !19)
 !19 = !{null}
 !20 = !{!21, !22}
 !21 = !DITemplateTypeParameter(name: "T", type: !10)
 !22 = !DITemplateValueParameter(type: !23, value: i32 (i32)* @"\01?bar@foo@@YAHH@Z")
 !23 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !8, size: 32, align: 32)
 !24 = !DILocation(line: 4, column: 17, scope: !17)
+!25 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S", file: !1, line: 7, size: 8, flags: DIFlagTypePassByValue, elements: !26, identifier: ".?AUS@@")
+!26 = !{!27}
+!27 = !DISubprogram(name: "operator<<", linkageName: "??6S@@QAEXH@Z", scope: !25, file: !1, line: 8, type: !28, scopeLine: 8, flags: DIFlagPrototyped, spFlags: 0)
+!28 = !DISubroutineType(cc: DW_CC_BORLAND_thiscall, types: !29)
+!29 = !{null, !30, !10}
+!30 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !25, size: 32, flags: DIFlagArtificial | DIFlagObjectPointer)
+!31 = distinct !DISubprogram(name: "operator<<", linkageName: "??6S@@QAEXH@Z", scope: !25, file: !1, line: 8, type: !28, scopeLine: 8, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, declaration: !27, retainedNodes: !2)
+!32 = !DILocation(line: 8, column: 27, scope: !31)
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