[PATCH] D45435: [CodeGen/AccelTable] Don't emit zero-CU name indexes

[Pavel Labath via Phabricator via llvm-commits]

labath created this revision.
labath added reviewers: JDevlieghere, aprantl, dblaikie.

If an input DICompileUnit is completely empty (e.g., the result of
running "clang -g" on an empty file), we don't bother emitting an empty
DWARF CU. When we do that, we must make sure we don't also emit a DWARF v5
name index, as DWARF specifies that each index must reference at least
one compilation unit.


Repository:
  rL LLVM

https://reviews.llvm.org/D45435

Files:
  lib/CodeGen/AsmPrinter/AccelTable.cpp
  lib/CodeGen/AsmPrinter/DwarfDebug.cpp
  test/DebugInfo/Generic/debug-names-empty-cu.ll


Index: test/DebugInfo/Generic/debug-names-empty-cu.ll
===================================================================
--- /dev/null
+++ test/DebugInfo/Generic/debug-names-empty-cu.ll
@@ -0,0 +1,19 @@
+; REQUIRES: object-emission
+; RUN: %llc_dwarf -accel-tables=Dwarf -filetype=obj -o %t < %s
+; RUN: llvm-dwarfdump -debug-names %t | FileCheck %s
+; RUN: llvm-dwarfdump -debug-names -verify %t | FileCheck --check-prefix=VERIFY %s
+
+; CHECK-NOT: CU count: 0
+; VERIFY: No errors.
+
+!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 7.0.0 (trunk 329543) (llvm/trunk 329551)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "-", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 7.0.0 (trunk 329543) (llvm/trunk 329551)"}
Index: lib/CodeGen/AsmPrinter/DwarfDebug.cpp
===================================================================
--- lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1468,6 +1468,10 @@
 }
 
 void DwarfDebug::emitAccelDebugNames() {
+  // Don't emit anything if we have no compilation units to index.
+  if (getUnits().empty())
+    return;
+
   Asm->OutStreamer->SwitchSection(
       Asm->getObjFileLowering().getDwarfDebugNamesSection());
   emitDWARF5AccelTable(Asm, AccelDebugNames, *this, getUnits());
Index: lib/CodeGen/AsmPrinter/AccelTable.cpp
===================================================================
--- lib/CodeGen/AsmPrinter/AccelTable.cpp
+++ lib/CodeGen/AsmPrinter/AccelTable.cpp
@@ -367,6 +367,7 @@
   Asm->emitInt16(Padding);
   Asm->OutStreamer->AddComment("Header: compilation unit count");
   Asm->emitInt32(CompUnitCount);
+  assert(CompUnitCount > 0);
   Asm->OutStreamer->AddComment("Header: local type unit count");
   Asm->emitInt32(LocalTypeUnitCount);
   Asm->OutStreamer->AddComment("Header: foreign type unit count");


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