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[codeview] Try to avoid emitting .cv_loc with line zero

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Summary:
Visual Studio doesn't like it while stepping. It kicks you out of the
source view of the file being stepped through and tries to fall back to
the disassembly view.

Fixes PR43530

The fix is incomplete, because it's possible to have a basic block with
no source locations at all. In this case, we don't emit a .cv_loc, but
that will result in wrong stepping behavior in the debugger if the
layout predecessor of the location-less BB has an unrelated source
location. We could try harder to find a valid location that dominates or
post-dominates the current BB, but in general it's a dataflow problem,
and one still might not exist. I left a FIXME about this.

As an alternative, we might want to consider having the middle-end check
if its emitting codeview and get it to stop using line zero.

Reviewers: akhuang

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68747

llvm-svn: 374267
This commit is contained in:
Reid Kleckner 2019-10-10 01:06:01 +00:00
parent b0ac285ee2
commit ff93e765b6
3 changed files with 91 additions and 4 deletions
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16
lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
View File

@ -2858,6 +2858,14 @@ void CodeViewDebug::endFunctionImpl(const MachineFunction *MF) {
CurFn = nullptr;
}
// Usable locations are valid with non-zero line numbers. A line number of zero
// corresponds to optimized code that doesn't have a distinct source location.
// In this case, we try to use the previous or next source location depending on
// the context.
static bool isUsableDebugLoc(DebugLoc DL) {
return DL && DL.getLine() != 0;
}
void CodeViewDebug::beginInstruction(const MachineInstr *MI) {
DebugHandlerBase::beginInstruction(MI);
@ -2869,19 +2877,21 @@ void CodeViewDebug::beginInstruction(const MachineInstr *MI) {
// If the first instruction of a new MBB has no location, find the first
// instruction with a location and use that.
DebugLoc DL = MI->getDebugLoc();
if (!DL && MI->getParent() != PrevInstBB) {
if (!isUsableDebugLoc(DL) && MI->getParent() != PrevInstBB) {
for (const auto &NextMI : *MI->getParent()) {
if (NextMI.isDebugInstr())
continue;
DL = NextMI.getDebugLoc();
if (DL)
if (isUsableDebugLoc(DL))
break;
}
// FIXME: Handle the case where the BB has no valid locations. This would
// probably require doing a real dataflow analysis.
}
PrevInstBB = MI->getParent();
// If we still don't have a debug location, don't record a location.
if (!DL)
if (!isUsableDebugLoc(DL))
return;
maybeRecordLocation(DL, Asm->MF);

77
test/DebugInfo/COFF/line-zero.ll Normal file
View File

@ -0,0 +1,77 @@
; RUN: llc < %s | FileCheck %s
; C++ source to regenerate:
; int main() {
; volatile int x;
; x = 1;
; #line 0
; x = 2;
; #line 7
; x = 3;
; }
; CHECK-LABEL: main: # @main
; CHECK: .cv_loc 0 1 1 0 # t.cpp:1:0
; CHECK: .cv_loc 0 1 3 0 # t.cpp:3:0
; CHECK: movl $1, 4(%rsp)
; CHECK-NOT: .cv_loc {{.*}} t.cpp:0:0
; CHECK: movl $2, 4(%rsp)
; CHECK: .cv_loc 0 1 7 0 # t.cpp:7:0
; CHECK: movl $3, 4(%rsp)
; CHECK: .cv_loc 0 1 8 0 # t.cpp:8:0
; CHECK: xorl %eax, %eax
; CHECK: retq
; ModuleID = 't.cpp'
source_filename = "t.cpp"
target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-windows-msvc19.22.27905"
; Function Attrs: norecurse nounwind uwtable
define dso_local i32 @main() local_unnamed_addr #0 !dbg !8 {
entry:
%x = alloca i32, align 4
%x.0.x.0..sroa_cast = bitcast i32* %x to i8*, !dbg !15
call void @llvm.dbg.declare(metadata i32* %x, metadata !13, metadata !DIExpression()), !dbg !15
store volatile i32 1, i32* %x, align 4, !dbg !16, !tbaa !17
store volatile i32 2, i32* %x, align 4, !dbg !21, !tbaa !17
store volatile i32 3, i32* %x, align 4, !dbg !22, !tbaa !17
ret i32 0, !dbg !23
}
; Function Attrs: nounwind readnone speculatable willreturn
declare void @llvm.dbg.declare(metadata, metadata, metadata) #2
attributes #0 = { norecurse nounwind uwtable }
attributes #1 = { argmemonly nounwind willreturn }
attributes #2 = { nounwind readnone speculatable willreturn }
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5, !6}
!llvm.ident = !{!7}
!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
!1 = !DIFile(filename: "t.cpp", directory: "C:\5Csrc\5Cllvm-project\5Cbuild", checksumkind: CSK_MD5, checksum: "8b6d53b166e6fa660f115eff7beedf3b")
!2 = !{}
!3 = !{i32 2, !"CodeView", i32 1}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = !{i32 1, !"wchar_size", i32 2}
!6 = !{i32 7, !"PIC Level", i32 2}
!7 = !{!"clang version 10.0.0"}
!8 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 1, type: !9, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !12)
!9 = !DISubroutineType(types: !10)
!10 = !{!11}
!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!12 = !{!13}
!13 = !DILocalVariable(name: "x", scope: !8, file: !1, line: 2, type: !14)
!14 = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: !11)
!15 = !DILocation(line: 2, scope: !8)
!16 = !DILocation(line: 3, scope: !8)
!17 = !{!18, !18, i64 0}
!18 = !{!"int", !19, i64 0}
!19 = !{!"omnipotent char", !20, i64 0}
!20 = !{!"Simple C++ TBAA"}
!21 = !DILocation(line: 0, scope: !8)
!22 = !DILocation(line: 7, scope: !8)
!23 = !DILocation(line: 8, scope: !8)

2
test/DebugInfo/COFF/local-variables.ll
View File

@ -60,7 +60,7 @@
; ASM: leaq 36(%rsp), %rcx
; ASM: [[else_end:\.Ltmp.*]]:
; ASM: .LBB0_3: # %if.end
; ASM: .cv_loc 0 1 0 0 # t.cpp:0:0
; ASM: .cv_loc 0 1 17 1 # t.cpp:17:1
; ASM: callq capture
; ASM: nop
; ASM: addq $56, %rsp