[codeview] Use comdats for debug info describing comdat functions

Summary:
This allows the linker to discard unused symbol information for comdat
functions that were discarded during the link. Before this change,
searching for the name of an inline function in the debugger would
return multiple results, one per symbol subsection in the object file.
After this change, there is only one result, the result for the function
chosen by the linker.

Reviewers: zturner, majnemer

Subscribers: aaboud, amccarth, llvm-commits

Differential Revision: http://reviews.llvm.org/D20642

llvm-svn: 270792

7 files changed, 261 insertions, 12 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index 0eb3e44fba1..3f3408eb368 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -18,6 +18,7 @@
 #include "llvm/DebugInfo/CodeView/TypeIndex.h"
 #include "llvm/DebugInfo/CodeView/TypeRecord.h"
 #include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCSectionCOFF.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/COFF.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
@@ -217,19 +218,19 @@ void CodeViewDebug::maybeRecordLocation(DebugLoc DL,
                         /*IsStmt=*/false, DL->getFilename());
 }
 
+void CodeViewDebug::emitCodeViewMagicVersion() {
+  OS.EmitValueToAlignment(4);
+  OS.AddComment("Debug section magic");
+  OS.EmitIntValue(COFF::DEBUG_SECTION_MAGIC, 4);
+}
+
 void CodeViewDebug::endModule() {
   if (FnDebugInfo.empty())
     return;
 
   emitTypeInformation();
 
-  // FIXME: For functions that are comdat, we should emit separate .debug$S
-  // sections that are comdat associative with the main function instead of
-  // having one big .debug$S section.
   assert(Asm != nullptr);
-  OS.SwitchSection(Asm->getObjFileLowering().getCOFFDebugSymbolsSection());
-  OS.AddComment("Debug section magic");
-  OS.EmitIntValue(COFF::DEBUG_SECTION_MAGIC, 4);
 
   // The COFF .debug$S section consists of several subsections, each starting
   // with a 4-byte control code (e.g. 0xF1, 0xF2, etc) and then a 4-byte length
@@ -237,12 +238,16 @@ void CodeViewDebug::endModule() {
   // aligned.
 
   // Make a subsection for all the inlined subprograms.
-  emitInlineeFuncIdsAndLines();
+  emitInlineeLinesSubsection();
 
   // Emit per-function debug information.
   for (auto &P : FnDebugInfo)
     emitDebugInfoForFunction(P.first, P.second);
 
+  // Switch back to the generic .debug$S section after potentially processing
+  // comdat symbol sections.
+  switchToDebugSectionForSymbol(nullptr);
+
   // This subsection holds a file index to offset in string table table.
   OS.AddComment("File index to string table offset subsection");
   OS.EmitCVFileChecksumsDirective();
@@ -275,9 +280,7 @@ void CodeViewDebug::emitTypeInformation() {
 
   // Start the .debug$T section with 0x4.
   OS.SwitchSection(Asm->getObjFileLowering().getCOFFDebugTypesSection());
-  OS.AddComment("Debug section magic");
-  OS.EmitValueToAlignment(4);
-  OS.EmitIntValue(COFF::DEBUG_SECTION_MAGIC, 4);
+  emitCodeViewMagicVersion();
 
   TypeTable.ForEachRecord(
       [&](TypeIndex Index, const MemoryTypeTableBuilder::Record *R) {
@@ -298,10 +301,13 @@ void CodeViewDebug::emitTypeInformation() {
       });
 }
 
-void CodeViewDebug::emitInlineeFuncIdsAndLines() {
+void CodeViewDebug::emitInlineeLinesSubsection() {
   if (InlinedSubprograms.empty())
     return;
 
+  // Use the generic .debug$S section.
+  switchToDebugSectionForSymbol(nullptr);
+
   MCSymbol *InlineBegin = MMI->getContext().createTempSymbol(),
            *InlineEnd = MMI->getContext().createTempSymbol();
 
@@ -401,6 +407,26 @@ void CodeViewDebug::emitInlinedCallSite(const FunctionInfo &FI,
   OS.EmitIntValue(SymbolKind::S_INLINESITE_END, 2); // RecordKind
 }
 
+void CodeViewDebug::switchToDebugSectionForSymbol(const MCSymbol *GVSym) {
+  // If we have a symbol, it may be in a section that is COMDAT. If so, find the
+  // comdat key. A section may be comdat because of -ffunction-sections or
+  // because it is comdat in the IR.
+  MCSectionCOFF *GVSec =
+      GVSym ? dyn_cast<MCSectionCOFF>(&GVSym->getSection()) : nullptr;
+  const MCSymbol *KeySym = GVSec ? GVSec->getCOMDATSymbol() : nullptr;
+
+  MCSectionCOFF *DebugSec = cast<MCSectionCOFF>(
+      Asm->getObjFileLowering().getCOFFDebugSymbolsSection());
+  DebugSec = OS.getContext().getAssociativeCOFFSection(DebugSec, KeySym);
+
+  OS.SwitchSection(DebugSec);
+
+  // Emit the magic version number if this is the first time we've switched to
+  // this section.
+  if (ComdatDebugSections.insert(DebugSec).second)
+    emitCodeViewMagicVersion();
+}
+
 void CodeViewDebug::emitDebugInfoForFunction(const Function *GV,
                                              FunctionInfo &FI) {
   // For each function there is a separate subsection
@@ -408,6 +434,9 @@ void CodeViewDebug::emitDebugInfoForFunction(const Function *GV,
   const MCSymbol *Fn = Asm->getSymbol(GV);
   assert(Fn);
 
+  // Switch to the to a comdat section, if appropriate.
+  switchToDebugSectionForSymbol(Fn);
+
   StringRef FuncName;
   if (auto *SP = GV->getSubprogram())
     FuncName = SP->getDisplayName();
diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
index 53e1aa0b422..df7c85c0007 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
@@ -101,6 +101,18 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
   };
   FunctionInfo *CurFn;
 
+  /// The set of comdat .debug$S sections that we've seen so far. Each section
+  /// must start with a magic version number that must only be emitted once.
+  /// This set tracks which sections we've already opened.
+  DenseSet<MCSectionCOFF *> ComdatDebugSections;
+
+  /// Switch to the appropriate .debug$S section for GVSym. If GVSym, the symbol
+  /// of an emitted global value, is in a comdat COFF section, this will switch
+  /// to a new .debug$S section in that comdat. This method ensures that the
+  /// section starts with the magic version number on first use. If GVSym is
+  /// null, uses the main .debug$S section.
+  void switchToDebugSectionForSymbol(const MCSymbol *GVSym);
+
   /// The next available function index for use with our .cv_* directives. Not
   /// to be confused with type indices for LF_FUNC_ID records.
   unsigned NextFuncId = 0;
@@ -148,9 +160,13 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
     FileToFilepathMap.clear();
   }
 
+  /// Emit the magic version number at the start of a CodeView type or symbol
+  /// section. Appears at the front of every .debug$S or .debug$T section.
+  void emitCodeViewMagicVersion();
+
   void emitTypeInformation();
 
-  void emitInlineeFuncIdsAndLines();
+  void emitInlineeLinesSubsection();
 
   void emitDebugInfoForFunction(const Function *GV, FunctionInfo &FI);
 
diff --git a/llvm/test/DebugInfo/COFF/asm.ll b/llvm/test/DebugInfo/COFF/asm.ll
index 5befe486e9d..be57e205468 100644
--- a/llvm/test/DebugInfo/COFF/asm.ll
+++ b/llvm/test/DebugInfo/COFF/asm.ll
@@ -22,6 +22,7 @@
 ; X86:      [[END_OF_F:.?Lfunc_end.*]]:
 ;
 ; X86-LABEL: .section        .debug$S,"dr"
+; X86-NEXT: .p2align 2
 ; X86-NEXT: .long   4
 ; Symbol subsection
 ; X86-NEXT: .long   241
@@ -114,6 +115,7 @@
 ; X64:      [[END_OF_F:.?Lfunc_end.*]]:
 ;
 ; X64-LABEL: .section        .debug$S,"dr"
+; X64-NEXT: .p2align 2
 ; X64-NEXT: .long   4
 ; Symbol subsection
 ; X64-NEXT: .long   241
diff --git a/llvm/test/DebugInfo/COFF/comdat.ll b/llvm/test/DebugInfo/COFF/comdat.ll
new file mode 100644
index 00000000000..94601b99899
--- /dev/null
+++ b/llvm/test/DebugInfo/COFF/comdat.ll
@@ -0,0 +1,196 @@
+; RUN: llc < %s | FileCheck %s
+
+; Verify that we get *two* .debug$S sections, the main one describing bar and
+; main, and one for f and fin$f, which is comdat with f.
+
+; Start in the main symbol section describing bar and main.
+
+; CHECK: .section .debug$S,"dr"{{$}}
+; CHECK: .long 4 # Debug section magic
+; CHECK: # Symbol subsection for bar
+; CHECK-NOT: Debug section magic
+; CHECK: # Symbol subsection for main
+
+; Emit symbol info for f and its associated code in a separate associated
+; section.
+
+; CHECK: .section .debug$S,"dr",associative,f{{$}}
+; CHECK: .long 4 # Debug section magic
+; CHECK: # Symbol subsection for f
+; CHECK-NOT: Debug section magic
+; CHECK: # Symbol subsection for ?fin$0@0@f@@
+
+; Switch back to the main section for the shared file checksum table and string
+; table.
+
+; CHECK: .section .debug$S,"dr"{{$}}
+; CHECK-NOT: Debug section magic
+; CHECK: .cv_filechecksums
+; CHECK: .cv_stringtable
+; CHECK-NOT: .section .debug$S,
+
+; Generated with this C++ source:
+; void foo();
+; void bar();
+; extern volatile int x;
+; inline void __declspec(noinline) f(bool c) {
+;   x++;
+;   if (c) {
+;     __try {
+;       foo();
+;     } __finally {
+;       x++;
+;     }
+;   } else
+;     bar();
+;   x++;
+; }
+; void bar() {
+;   x++;
+; }
+; int main() {
+;   f(true);
+; }
+
+; ModuleID = 't.cpp'
+source_filename = "t.cpp"
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.0.23918"
+
+$f = comdat any
+
+@x = external global i32, align 4
+
+; Function Attrs: norecurse nounwind uwtable
+define void @bar() #0 !dbg !7 {
+entry:
+  %0 = load volatile i32, i32* @x, align 4, !dbg !10, !tbaa !11
+  %inc = add nsw i32 %0, 1, !dbg !10
+  store volatile i32 %inc, i32* @x, align 4, !dbg !10, !tbaa !11
+  ret void, !dbg !15
+}
+
+; Function Attrs: nounwind uwtable
+define i32 @main() #1 !dbg !16 {
+entry:
+  tail call void @f(i32 1), !dbg !20
+  ret i32 0, !dbg !21
+}
+
+; Function Attrs: inlinehint noinline nounwind uwtable
+define linkonce_odr void @f(i32 %c) #2 comdat personality i8* bitcast (i32 (...)* @__C_specific_handler to i8*) !dbg !22 {
+entry:
+  tail call void @llvm.dbg.value(metadata i32 %c, i64 0, metadata !26, metadata !27), !dbg !28
+  %0 = load volatile i32, i32* @x, align 4, !dbg !29, !tbaa !11
+  %inc = add nsw i32 %0, 1, !dbg !29
+  store volatile i32 %inc, i32* @x, align 4, !dbg !29, !tbaa !11
+  %tobool = icmp eq i32 %c, 0, !dbg !30
+  br i1 %tobool, label %if.else, label %if.then, !dbg !32
+
+if.then:                                          ; preds = %entry
+  invoke void bitcast (void (...)* @foo to void ()*)() #6
+          to label %invoke.cont unwind label %ehcleanup, !dbg !33
+
+invoke.cont:                                      ; preds = %if.then
+  tail call fastcc void @"\01?fin$0@0@f@@"() #7, !dbg !36
+  br label %if.end, !dbg !37
+
+ehcleanup:                                        ; preds = %if.then
+  %1 = cleanuppad within none [], !dbg !36
+  tail call fastcc void @"\01?fin$0@0@f@@"() #7 [ "funclet"(token %1) ], !dbg !36
+  cleanupret from %1 unwind to caller, !dbg !36
+
+if.else:                                          ; preds = %entry
+  tail call void @bar(), !dbg !38
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %invoke.cont
+  %2 = load volatile i32, i32* @x, align 4, !dbg !39, !tbaa !11
+  %inc1 = add nsw i32 %2, 1, !dbg !39
+  store volatile i32 %inc1, i32* @x, align 4, !dbg !39, !tbaa !11
+  ret void, !dbg !40
+}
+
+; Function Attrs: nounwind
+define internal fastcc void @"\01?fin$0@0@f@@"() unnamed_addr #3 comdat($f) !dbg !41 {
+entry:
+  tail call void @llvm.dbg.value(metadata i8* null, i64 0, metadata !44, metadata !27), !dbg !48
+  tail call void @llvm.dbg.value(metadata i8 0, i64 0, metadata !46, metadata !27), !dbg !48
+  %0 = load volatile i32, i32* @x, align 4, !dbg !49, !tbaa !11
+  %inc = add nsw i32 %0, 1, !dbg !49
+  store volatile i32 %inc, i32* @x, align 4, !dbg !49, !tbaa !11
+  ret void, !dbg !51
+}
+
+declare void @foo(...) #4
+
+declare i32 @__C_specific_handler(...)
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #5
+
+attributes #0 = { norecurse nounwind uwtable "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind uwtable "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { inlinehint noinline nounwind uwtable "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #3 = { nounwind "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #4 = { "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #5 = { nounwind readnone }
+attributes #6 = { noinline }
+attributes #7 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.9.0 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "t.cpp", directory: "D:\5Csrc\5Cllvm\5Cbuild")
+!2 = !{}
+!3 = !{i32 2, !"CodeView", i32 1}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"PIC Level", i32 2}
+!6 = !{!"clang version 3.9.0 "}
+!7 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 19, type: !8, isLocal: false, isDefinition: true, scopeLine: 19, isOptimized: true, unit: !0, variables: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null}
+!10 = !DILocation(line: 20, column: 4, scope: !7)
+!11 = !{!12, !12, i64 0}
+!12 = !{!"int", !13, i64 0}
+!13 = !{!"omnipotent char", !14, i64 0}
+!14 = !{!"Simple C/C++ TBAA"}
+!15 = !DILocation(line: 21, column: 1, scope: !7)
+!16 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 22, type: !17, isLocal: false, isDefinition: true, scopeLine: 22, isOptimized: true, unit: !0, variables: !2)
+!17 = !DISubroutineType(types: !18)
+!18 = !{!19}
+!19 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!20 = !DILocation(line: 23, column: 3, scope: !16)
+!21 = !DILocation(line: 24, column: 1, scope: !16)
+!22 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 5, type: !23, isLocal: false, isDefinition: true, scopeLine: 5, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !25)
+!23 = !DISubroutineType(types: !24)
+!24 = !{null, !19}
+!25 = !{!26}
+!26 = !DILocalVariable(name: "c", arg: 1, scope: !22, file: !1, line: 5, type: !19)
+!27 = !DIExpression()
+!28 = !DILocation(line: 5, column: 40, scope: !22)
+!29 = !DILocation(line: 6, column: 4, scope: !22)
+!30 = !DILocation(line: 7, column: 7, scope: !31)
+!31 = distinct !DILexicalBlock(scope: !22, file: !1, line: 7, column: 7)
+!32 = !DILocation(line: 7, column: 7, scope: !22)
+!33 = !DILocation(line: 9, column: 7, scope: !34)
+!34 = distinct !DILexicalBlock(scope: !35, file: !1, line: 8, column: 11)
+!35 = distinct !DILexicalBlock(scope: !31, file: !1, line: 7, column: 10)
+!36 = !DILocation(line: 10, column: 5, scope: !34)
+!37 = !DILocation(line: 13, column: 3, scope: !35)
+!38 = !DILocation(line: 14, column: 5, scope: !31)
+!39 = !DILocation(line: 15, column: 4, scope: !22)
+!40 = !DILocation(line: 16, column: 1, scope: !22)
+!41 = distinct !DISubprogram(linkageName: "\01?fin$0@0@f@@", scope: !1, file: !1, line: 10, type: !42, isLocal: true, isDefinition: true, scopeLine: 10, flags: DIFlagArtificial, isOptimized: true, unit: !0, variables: !43)
+!42 = !DISubroutineType(types: !2)
+!43 = !{!44, !46}
+!44 = !DILocalVariable(name: "frame_pointer", arg: 2, scope: !41, type: !45, flags: DIFlagArtificial)
+!45 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64, align: 64)
+!46 = !DILocalVariable(name: "abnormal_termination", arg: 1, scope: !41, type: !47, flags: DIFlagArtificial | DIFlagObjectPointer)
+!47 = !DIBasicType(name: "unsigned char", size: 8, align: 8, encoding: DW_ATE_unsigned_char)
+!48 = !DILocation(line: 0, scope: !41)
+!49 = !DILocation(line: 11, column: 8, scope: !50)
+!50 = distinct !DILexicalBlock(scope: !41, file: !1, line: 10, column: 17)
+!51 = !DILocation(line: 12, column: 5, scope: !41)
diff --git a/llvm/test/DebugInfo/COFF/multifile.ll b/llvm/test/DebugInfo/COFF/multifile.ll
index fec7bf03e46..06b3d0e3605 100644
--- a/llvm/test/DebugInfo/COFF/multifile.ll
+++ b/llvm/test/DebugInfo/COFF/multifile.ll
@@ -31,6 +31,7 @@
 ; X86:      [[END_OF_F:.?Lfunc_end.*]]:
 ;
 ; X86-LABEL: .section        .debug$S,"dr"
+; X86-NEXT: .p2align 2
 ; X86-NEXT: .long   4
 ; Symbol subsection
 ; X86-NEXT: .long   241
@@ -138,6 +139,7 @@
 ; X64:      [[END_OF_F:.?Lfunc_end.*]]:
 ;
 ; X64-LABEL: .section        .debug$S,"dr"
+; X64-NEXT: .p2align 2
 ; X64-NEXT: .long   4
 ; Symbol subsection
 ; X64-NEXT: .long   241
diff --git a/llvm/test/DebugInfo/COFF/multifunction.ll b/llvm/test/DebugInfo/COFF/multifunction.ll
index bdceebf6704..d61681c7241 100644
--- a/llvm/test/DebugInfo/COFF/multifunction.ll
+++ b/llvm/test/DebugInfo/COFF/multifunction.ll
@@ -52,6 +52,7 @@
 ; X86:      [[END_OF_F:.?Lfunc_end.*]]:
 ;
 ; X86-LABEL: .section        .debug$S,"dr"
+; X86-NEXT: .p2align 2
 ; X86-NEXT: .long   4
 ; Symbol subsection for x
 ; X86-NEXT: .long   241
@@ -315,6 +316,7 @@
 ; X64:      [[END_OF_F:.?Lfunc_end.*]]:
 ;
 ; X64-LABEL: .section        .debug$S,"dr"
+; X64-NEXT: .p2align 2
 ; X64-NEXT: .long   4
 ; Symbol subsection for x
 ; X64-NEXT: .long   241
diff --git a/llvm/test/DebugInfo/COFF/simple.ll b/llvm/test/DebugInfo/COFF/simple.ll
index 590e8b146c8..5c9bb2557dc 100644
--- a/llvm/test/DebugInfo/COFF/simple.ll
+++ b/llvm/test/DebugInfo/COFF/simple.ll
@@ -21,6 +21,7 @@
 ; X86:      [[END_OF_F:Lfunc_end.*]]:
 ;
 ; X86-LABEL: .section        .debug$S,"dr"
+; X86-NEXT: .p2align 2
 ; X86-NEXT: .long   4
 ; Symbol subsection
 ; X86-NEXT: .long   241
@@ -110,6 +111,7 @@
 ; X64:      [[END_OF_F:.?Lfunc_end.*]]:
 ;
 ; X64-LABEL: .section        .debug$S,"dr"
+; X64-NEXT: .p2align 2
 ; X64-NEXT: .long   4
 ; Symbol subsection
 ; X64-NEXT: .long   241