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[DebugInfo][LiveDebugValues] Teach Live Debug Values About Meta Instructions 

Previously LiveDebugValues pass would consider meta instructions that 'fiddle' with liveness of registers as register definitions when transfering register defs. This would mean that, for example, a KILL instruction would cause LiveDebugValues to terminate the range of an earlier DBG_VALUE instruction resulting in the none propogation of said DBG_VALUE instructions into later blocks.

This patch adds the check and a helpful comment, fixes a test that previously tested for the broken behaviour by coincidence and adds a test specifically for this.

reviewers: vsk, dstenb, djtodoro

Differential Revision: https://reviews.llvm.org/D73210
This commit is contained in:
Tom Weaver 2020-01-24 16:29:05 +00:00
parent 1484d0f12a
commit f5147765ba
3 changed files with 70 additions and 1 deletions
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6
llvm/lib/CodeGen/LiveDebugValues.cpp
View File

@ -922,6 +922,12 @@ void LiveDebugValues::insertTransferDebugPair(
void LiveDebugValues::transferRegisterDef(
MachineInstr &MI, OpenRangesSet &OpenRanges, VarLocMap &VarLocIDs,
TransferMap &Transfers) {
// Meta Instructions do not affect the debug liveness of any register they
// define.
if (MI.isMetaInstruction())
return;
MachineFunction *MF = MI.getMF();
const TargetLowering *TLI = MF->getSubtarget().getTargetLowering();
unsigned SP = TLI->getStackPointerRegisterToSaveRestore();

1
llvm/test/DebugInfo/MIR/X86/entry-value-of-modified-param.mir
View File

@ -19,7 +19,6 @@
# CHECK: ![[ARG_A:.*]] = !DILocalVariable(name: "a"
# CHECK: ![[ARG_B:.*]] = !DILocalVariable(name: "b"
# CHECK: ![[ARG_C:.*]] = !DILocalVariable(name: "c"
# CHECK: DBG_VALUE $edi, $noreg, ![[ARG_A]], !DIExpression(DW_OP_LLVM_entry_value, 1)
# CHECK: DBG_VALUE $edx, $noreg, ![[ARG_C]], !DIExpression(DW_OP_LLVM_entry_value, 1)
# CHECK: DBG_VALUE $edi, $noreg, ![[ARG_A]], !DIExpression(DW_OP_LLVM_entry_value, 1)
# CHECK-NOT: DBG_VALUE $esi, $noreg, ![[ARG_B]], !DIExpression(DW_OP_LLVM_entry_value, 1)

64
llvm/test/DebugInfo/MIR/X86/livedebugvalues-ignores-metaInstructions.mir Normal file
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@ -0,0 +1,64 @@
--- |
; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
; Check that live-debug-values ignores meta instructions.
; CHECK-LABEL: bb.0.entry:
; CHECK: DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
; CHECK-LABEL: bb.1.bb1:
; CHECK: DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
; CHECK-LABEL: bb.2.bb2:
; CHECK: DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
; CHECK-LABEL: bb.3.bb3:
; CHECK: DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
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:
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
DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
bb.1.bb1:
successors: %bb.2
renamable $ebx = KILL $ebx
bb.2.bb2:
successors: %bb.3
renamable $ebx = KILL $ebx
bb.3.bb3:
RETQ $eax, debug-location !17
...