livedebugvalues_downgradefeedback_loop.mir

--- |
  ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - -experimental-debug-variable-locations | FileCheck %s -implicit-check-not=DBG_VALUE

  define i32 @_Z8bb_to_bb() local_unnamed_addr !dbg !12 {
  entry:
    br label %bb1, !dbg !17
  bb1:
    br label %bb2, !dbg !17
  bb2:
    br label %bb3, !dbg !17
  bb3:
    br label %bb3, !dbg !17
  bb4:
    br label %bb3, !dbg !17
  bb5:
    ret i32 0, !dbg !17
  }

  !llvm.dbg.cu = !{!0}
  !llvm.module.flags = !{!7, !8, !9, !10}
  !llvm.ident = !{!11}
  !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 10.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3, debugInfoForProfiling: true, nameTableKind: None)
  !1 = !DIFile(filename: "main.cpp", directory: "F:\")
  !2 = !{}
  !3 = !{!4}
  !4 = !DIGlobalVariableExpression(var: !5, expr: !DIExpression())
  !5 = distinct !DIGlobalVariable(name: "start", scope: !0, file: !1, line: 4, type: !6, isLocal: false, isDefinition: true)
  !6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
  !7 = !{i32 2, !"Dwarf Version", i32 4}
  !8 = !{i32 2, !"Debug Info Version", i32 3}
  !9 = !{i32 1, !"wchar_size", i32 2}
  !10 = !{i32 7, !"PIC Level", i32 2}
  !11 = !{!"clang version 10.0.0"}
  !12 = distinct !DISubprogram(name: "bb_to_bb", linkageName: "bb_to_bb", scope: !1, file: !1, line: 6, type: !13, scopeLine: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !15)
  !13 = !DISubroutineType(types: !14)
  !14 = !{!6, !6}
  !15 = !{!16}
  !16 = !DILocalVariable(name: "myVar", scope: !12, file: !1, line: 7, type: !6)
  !17 = !DILocation(line: 10, scope: !12)

...
---
name: _Z8bb_to_bb
body:  |
  bb.0.entry:
    successors: %bb.1
    $ebx = MOV32ri 0, debug-location !17
    $eax = COPY $ebx
    DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
  bb.1.bb1:
    successors: %bb.2
    $eax = COPY $ebx, debug-location !17
    $ebx = COPY $ecx, debug-location !17
    DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
  bb.2.bb2:
    successors: %bb.3, %bb.4
    JCC_1 %bb.4, 4, implicit $eflags
  bb.3.bb3:
    successors: %bb.5
    $ebx = MOV32ri 0, debug-location !17
    DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
    JMP_1 %bb.5
  bb.4.bb4:
    successors: %bb.5
  bb.5.bb5:
    successors: %bb.2, %bb.6
    JCC_1 %bb.2, 4, implicit killed $eflags
  bb.6:
    successors: %bb.1, %bb.7
    JCC_1 %bb.1, 4, implicit killed $eflags
  bb.7:
    RETQ $eax, debug-location !17
...

Two nested loops in this file, with diamond if-then-else in the inner loop. Using VarLoc based LDV:

build/bin/llc llvm/test/DebugInfo/MIR/InstrRef/livedebugvalues_downgradefeedback_loop.mir -march=x86-64 -run-pass=livedebugvalues -o -

Produces a live-in variable location of ebx for block two. Using -experimental-debug-variable-locations to enable InstrRefBasedLDV, no live-in variable location is created.