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[DebugInfo] Emit a 1-byte value as a terminator of entries list in the name index. 

As stated in section 6.1.1.2, DWARFv5, p. 142,
| The last entry for each name is followed by a zero byte that
| terminates the list. There may be gaps between the lists.

The patch changes emitting a 4-byte zero value to a 1-byte one, which
effectively removes the gap between entry lists, and thus saves
approximately 3 bytes per name; the calculation is not exact because
the total size of the table is aligned to 4.

Differential Revision: https://reviews.llvm.org/D86927
This commit is contained in:
Igor Kudrin 2020-09-02 16:12:39 +07:00
parent 71eed4808f
commit 3445ec9ba7
2 changed files with 25 additions and 1 deletions
llvm
lib/CodeGen/AsmPrinter
AccelTable.cpp
test/DebugInfo/X86
debug-names-end-of-list.ll

2
llvm/lib/CodeGen/AsmPrinter/AccelTable.cpp
View File

@ -505,7 +505,7 @@ template <typename DataT> void Dwarf5AccelTableWriter<DataT>::emitData() const {
for (const auto *Value : Hash->Values)
emitEntry(*static_cast<const DataT *>(Value));
Asm->OutStreamer->AddComment("End of list: " + Hash->Name.getString());
Asm->emitInt32(0);
Asm->emitInt8(0);
}
}
}

24
llvm/test/DebugInfo/X86/debug-names-end-of-list.ll Normal file
View File

@ -0,0 +1,24 @@
; This checks that the list of index entries in the name index is terminated
; with a 1-byte value.
; RUN: llc -mtriple x86_64 -accel-tables=Dwarf -dwarf-version=5 -filetype=asm %s -o - | \
; RUN: FileCheck %s
; CHECK: .section .debug_names,"",@progbits
; CHECK: .Lnames_entries0:
; CHECK: .byte 0 # End of list: int
; CHECK: .byte 0 # End of list: foo
@foo = common dso_local global i32 0, align 4, !dbg !5
!llvm.dbg.cu = !{!2}
!llvm.module.flags = !{!0}
!0 = !{i32 2, !"Debug Info Version", i32 3}
!1 = !DIFile(filename: "foo.c", directory: "/tmp")
!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "Manual", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !3, globals: !4)
!3 = !{}
!4 = !{!5}
!5 = !DIGlobalVariableExpression(var: !6, expr: !DIExpression())
!6 = distinct !DIGlobalVariable(name: "foo", scope: !2, file: !1, line: 1, type: !7, isLocal: false, isDefinition: true)
!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)