| Issue |
55515
|
| Summary |
Debug location information dropped unnecessarily in div-rem-pairs optimization pass.
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
cbossut7
|
Overview: In the attached example, the div-rem-pairs pass will drop debug location unnecessarily.
Steps to reproduce (files attached at the end):
Here is the version of llvm:
$ ../llvm-build/bin/clang++ --version
clang version 15.0.0 (https://github.com/llvm/llvm-project.git f422c5d87142cc1dc65cf7fb15444c2afc810611)
Target: x86_64-unknown-linux-gnu
Thread model: posix
$ opt -div-rem-pairs debugified_out.ll > debugified_opt.bc
$ llvm-dis debugified_opt.bc
$ diff debugified_out.ll debugified_opt.ll
1c1
< ; ModuleID = 'bugpoint-reduced-simplified.ll'
---
> ; ModuleID = 'debugified_out.ll'
3c3
< target triple = "x86_64-unknown-linux-gnu"
---
> target triple = "x86_64-unknown-unknown"
11,12c11,12
< %rem = sub i16 %a, %t0, !dbg !15
< call void @llvm.dbg.value(metadata i16 %rem, metadata !12, metadata !DIExpression()), !dbg !15
---
> %rem.recomposed = srem i16 %a, %b
> call void @llvm.dbg.value(metadata i16 %rem.recomposed, metadata !12, metadata !DIExpression()), !dbg !15
The variable %rem seems to have a one-to-one relationship with %rem.recomposed, so it seems the debug location !15 is unnecessarily dropped, according to the principles in:
https://llvm.org/docs/HowToUpdateDebugInfo.html
There's a one-to-one relationship between the new and old instruction, and it's placed in the same location, so the DebugLoc should be preserved in the reproducer.
Relevant files:
File 1—------------------------------------------------------------------------------
$ cat debugified_out.ll
; ModuleID = 'bugpoint-reduced-simplified.ll'
source_filename = "div-expanded-rem-pair.ll"
target triple = "x86_64-unknown-linux-gnu"
define void @hoist_srem(i16 %a, i16 %b) !dbg !5 {
entry:
%div = sdiv i16 %a, %b, !dbg !13
call void @llvm.dbg.value(metadata i16 %div, metadata !9, metadata !DIExpression()), !dbg !13
%t0 = mul i16 %div, %b, !dbg !14
call void @llvm.dbg.value(metadata i16 %t0, metadata !11, metadata !DIExpression()), !dbg !14
%rem = sub i16 %a, %t0, !dbg !15
call void @llvm.dbg.value(metadata i16 %rem, metadata !12, metadata !DIExpression()), !dbg !15
unreachable, !dbg !16
}
; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
declare void @llvm.dbg.value(metadata, metadata, metadata) #0
attributes #0 = { nofree nosync nounwind readnone speculatable willreturn }
!llvm.dbg.cu = !{!0}
!llvm.debugify = !{!2, !3}
!llvm.module.flags = !{!4}
!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
!1 = !DIFile(filename: "bugpoint-reduced-simplified.ll", directory: "/")
!2 = !{i32 4}
!3 = !{i32 3}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = distinct !DISubprogram(name: "hoist_srem", linkageName: "hoist_srem", scope: null, file: !1, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
!6 = !DISubroutineType(types: !7)
!7 = !{}
!8 = !{!9, !11, !12}
!9 = !DILocalVariable(name: "1", scope: !5, file: !1, line: 1, type: !10)
!10 = !DIBasicType(name: "ty16", size: 16, encoding: DW_ATE_unsigned)
!11 = !DILocalVariable(name: "2", scope: !5, file: !1, line: 2, type: !10)
!12 = !DILocalVariable(name: "3", scope: !5, file: !1, line: 3, type: !10)
!13 = !DILocation(line: 1, column: 1, scope: !5)
!14 = !DILocation(line: 2, column: 1, scope: !5)
!15 = !DILocation(line: 3, column: 1, scope: !5)
!16 = !DILocation(line: 4, column: 1, scope: !5)
File 2-----------------------------------------------------------------------
$ cat debugified_opt.ll
; ModuleID = 'debugified_out.ll'
source_filename = "div-expanded-rem-pair.ll"
target triple = "x86_64-unknown-unknown"
define void @hoist_srem(i16 %a, i16 %b) !dbg !5 {
entry:
%div = sdiv i16 %a, %b, !dbg !13
call void @llvm.dbg.value(metadata i16 %div, metadata !9, metadata !DIExpression()), !dbg !13
%t0 = mul i16 %div, %b, !dbg !14
call void @llvm.dbg.value(metadata i16 %t0, metadata !11, metadata !DIExpression()), !dbg !14
%rem.recomposed = srem i16 %a, %b
call void @llvm.dbg.value(metadata i16 %rem.recomposed, metadata !12, metadata !DIExpression()), !dbg !15
unreachable, !dbg !16
}
; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
declare void @llvm.dbg.value(metadata, metadata, metadata) #0
attributes #0 = { nofree nosync nounwind readnone speculatable willreturn }
!llvm.dbg.cu = !{!0}
!llvm.debugify = !{!2, !3}
!llvm.module.flags = !{!4}
!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
!1 = !DIFile(filename: "bugpoint-reduced-simplified.ll", directory: "/")
!2 = !{i32 4}
!3 = !{i32 3}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = distinct !DISubprogram(name: "hoist_srem", linkageName: "hoist_srem", scope: null, file: !1, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
!6 = !DISubroutineType(types: !7)
!7 = !{}
!8 = !{!9, !11, !12}
!9 = !DILocalVariable(name: "1", scope: !5, file: !1, line: 1, type: !10)
!10 = !DIBasicType(name: "ty16", size: 16, encoding: DW_ATE_unsigned)
!11 = !DILocalVariable(name: "2", scope: !5, file: !1, line: 2, type: !10)
!12 = !DILocalVariable(name: "3", scope: !5, file: !1, line: 3, type: !10)
!13 = !DILocation(line: 1, column: 1, scope: !5)
!14 = !DILocation(line: 2, column: 1, scope: !5)
!15 = !DILocation(line: 3, column: 1, scope: !5)
!16 = !DILocation(line: 4, column: 1, scope: !5)
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