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[DWARF] Add option to add linkage_names to call_origin declaration refs #89640

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Apr 23, 2024
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[DWARF] Add option to add linkage_names to call_origin declaration refs #89640

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[DWARF] Add option to add linkage_names to call_origin declaration refs
OCHyams Apr 4, 2024
090e97e
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OCHyams Apr 23, 2024
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21 changes: 21 additions & 0 deletions llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,7 @@
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCSymbolWasm.h"
#include "llvm/MC/MachineLocation.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
Expand All @@ -42,6 +43,20 @@

using namespace llvm;

/// Query value using AddLinkageNamesToDeclCallOriginsForTuning.
cl::opt<cl::boolOrDefault> AddLinkageNamesToDeclCallOrigins(
"add-linkage-names-to-declaration-call-origins", cl::Hidden,
cl::desc("Add DW_AT_linkage_name to function declaration DIEs "
"referenced by DW_AT_call_origin attributes. Enabled by default "
"for -gsce debugger tuning."));

Comment on lines +46 to +52
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I think we /generally/ try not to use/add raw cl::opts, and instead pass things through the driver/frontend flag handling? (I might be wrong, if there's substantial precedent, let me know)

& not sure how this sits with @pogo59's general premise that debugger tuning shouldn't be reachable only through the tuning flags, but should be independently accessible (does independently accessible mean supported in the driver flags, or is -Xclang/cc1/mllvm flags sufficient to meet that requirement?)

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FWIW -dwarf-linkage-names is an -mllvm flag too (happy to move the flag around as needed though - I don't have a strong opinion on it)

static bool AddLinkageNamesToDeclCallOriginsForTuning(const DwarfDebug *DD) {
bool EnabledByDefault = DD->tuneForSCE();
if (EnabledByDefault)
return AddLinkageNamesToDeclCallOrigins != cl::boolOrDefault::BOU_FALSE;
return AddLinkageNamesToDeclCallOrigins == cl::boolOrDefault::BOU_TRUE;
}

static dwarf::Tag GetCompileUnitType(UnitKind Kind, DwarfDebug *DW) {

// According to DWARF Debugging Information Format Version 5,
Expand Down Expand Up @@ -1260,6 +1275,12 @@ DIE &DwarfCompileUnit::constructCallSiteEntryDIE(DIE &ScopeDIE,
} else {
DIE *CalleeDIE = getOrCreateSubprogramDIE(CalleeSP);
assert(CalleeDIE && "Could not create DIE for call site entry origin");
if (AddLinkageNamesToDeclCallOriginsForTuning(DD) &&
!CalleeSP->isDefinition() &&
!CalleeDIE->findAttribute(dwarf::DW_AT_linkage_name)) {
addLinkageName(*CalleeDIE, CalleeSP->getLinkageName());
}

addDIEEntry(CallSiteDIE, getDwarf5OrGNUAttr(dwarf::DW_AT_call_origin),
*CalleeDIE);
}
Expand Down
96 changes: 96 additions & 0 deletions llvm/test/DebugInfo/X86/call-origin-linkage-names.ll
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@@ -0,0 +1,96 @@
; RUN: llc %s --filetype=obj -o - -dwarf-linkage-names=Abstract -add-linkage-names-to-declaration-call-origins=false \
; RUN: | llvm-dwarfdump - | FileCheck %s --check-prefixes=COMMON,DISABLE --implicit-check-not=DW_AT_linkage_name
; RUN: llc %s --filetype=obj -o - -dwarf-linkage-names=Abstract -add-linkage-names-to-declaration-call-origins=true \
; RUN: | llvm-dwarfdump - | FileCheck %s --check-prefixes=COMMON,ENABLE --implicit-check-not=DW_AT_linkage_name

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Do we want more RUN lines showing default varies with tuning? I'm inclined to think it's not super necessary but curious what other reviewers think.

;; Check that -add-linkage-names-to-declaration-call-origins controls whether
;; linkage names are added to declarations referenced by DW_AT_call_origin
;; attributes.
;;
;; $ cat test.cpp
;; void a();
;; __attribute__((optnone))
;; void b() {}
;; void c();
;; extern "C" {
;; void d();
;; }
;;
;; void e() {
;; a(); //< Reference declaration DIE (add linkage name).
;; b(); //< Reference definition DIE (don't add linkage name).
;; c(); //< Reference definition DIE (don't add linkage name).
;; d(); //< Reference declaration DIE, but there's no linkage name.
;; }
;;
;; __attribute__((optnone))
;; void c() {}
;; $ clang++ -emit-llvm -S -O1 -g

; COMMON: DW_TAG_call_site
; ENABLE-NEXT: DW_AT_call_origin (0x[[a:[a-z0-9]+]] "_Z1av")
; DISABLE-NEXT: DW_AT_call_origin (0x[[a:[a-z0-9]+]] "a")
; COMMON: DW_TAG_call_site
; COMMON-NEXT: DW_AT_call_origin (0x[[b:[a-z0-9]+]] "b")
; COMMON: DW_TAG_call_site
; COMMON-NEXT: DW_AT_call_origin (0x[[c:[a-z0-9]+]] "c")
; COMMON: DW_TAG_call_site
; COMMON-NEXT: DW_AT_call_origin (0x[[d:[a-z0-9]+]] "d")

; COMMON: 0x[[a]]: DW_TAG_subprogram
; COMMON: DW_AT_name ("a")
; ENABLE: DW_AT_linkage_name ("_Z1av")
; COMMON: 0x[[b]]: DW_TAG_subprogram
; COMMON: DW_AT_name ("b")
; COMMON: 0x[[c]]: DW_TAG_subprogram
; COMMON: DW_AT_name ("c")
; COMMON: 0x[[d]]: DW_TAG_subprogram
; COMMON: DW_AT_name ("d")

target triple = "x86_64-unknown-linux-gnu"

define dso_local void @_Z1ev() local_unnamed_addr !dbg !13 {
entry:
tail call void @_Z1av(), !dbg !14
tail call void @_Z1bv(), !dbg !15
tail call void @_Z1cv(), !dbg !16
tail call void @d(), !dbg !17
ret void, !dbg !18
}

define dso_local void @_Z1bv() local_unnamed_addr !dbg !9 {
entry:
ret void, !dbg !12
}

declare !dbg !19 void @_Z1av() local_unnamed_addr

define dso_local void @_Z1cv() local_unnamed_addr !dbg !20 {
entry:
ret void, !dbg !21
}
declare !dbg !22 void @d() local_unnamed_addr

!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!2, !3}
!llvm.ident = !{!8}

!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 19.0.0git", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
!1 = !DIFile(filename: "test.cpp", directory: "/")
!2 = !{i32 7, !"Dwarf Version", i32 5}
!3 = !{i32 2, !"Debug Info Version", i32 3}
!8 = !{!"clang version 19.0.0"}
!9 = distinct !DISubprogram(name: "b", linkageName: "_Z1bv", scope: !1, file: !1, line: 3, type: !10, scopeLine: 3, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
!10 = !DISubroutineType(types: !11)
!11 = !{null}
!12 = !DILocation(line: 3, column: 11, scope: !9)
!13 = distinct !DISubprogram(name: "e", linkageName: "_Z1ev", scope: !1, file: !1, line: 9, type: !10, scopeLine: 9, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
!14 = !DILocation(line: 10, column: 3, scope: !13)
!15 = !DILocation(line: 11, column: 3, scope: !13)
!16 = !DILocation(line: 12, column: 3, scope: !13)
!17 = !DILocation(line: 13, column: 3, scope: !13)
!18 = !DILocation(line: 14, column: 1, scope: !13)
!19 = !DISubprogram(name: "a", linkageName: "_Z1av", scope: !1, file: !1, line: 1, type: !10, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized)
!20 = distinct !DISubprogram(name: "c", linkageName: "_Z1cv", scope: !1, file: !1, line: 17, type: !10, scopeLine: 17, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
!21 = !DILocation(line: 17, column: 11, scope: !20)
!22 = !DISubprogram(name: "d", scope: !1, file: !1, line: 6, type: !10, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized)
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