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[codeview] Use the first valid source location at the top of every MBB

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If the instructions at the beginning of the block have no location,
we're better off using the location of the first instruction in the
current basic block. At the very least, that instruction post-dominates
this one, whereas if we don't emit a .cv_loc directive, we end up using
the potentially invalid location that falls through from the previous
block.

We could probably do better here by emitting some kind of ".cv_loc end"
directive that stops the line table entry of the previous .cv_loc
directive from bleeding out of its basic block. This would improve the
line table when an entire MBB has no valid location info.

llvm-svn: 306889
This commit is contained in:
Reid Kleckner 2017-06-30 21:33:44 +00:00
parent 78a6e492bf
commit 0271f6ebc2
4 changed files with 116 additions and 6 deletions
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22
lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
View File

@ -365,7 +365,7 @@ static void addLocIfNotPresent(SmallVectorImpl<const DILocation *> &Locs,
void CodeViewDebug::maybeRecordLocation(const DebugLoc &DL,
const MachineFunction *MF) {
// Skip this instruction if it has the same location as the previous one.
if (DL == CurFn->LastLoc)
if (!DL || DL == PrevInstLoc)
return;
const DIScope *Scope = DL.get()->getScope();
@ -385,11 +385,11 @@ void CodeViewDebug::maybeRecordLocation(const DebugLoc &DL,
if (!CurFn->HaveLineInfo)
CurFn->HaveLineInfo = true;
unsigned FileId = 0;
if (CurFn->LastLoc.get() && CurFn->LastLoc->getFile() == DL->getFile())
if (PrevInstLoc.get() && PrevInstLoc->getFile() == DL->getFile())
FileId = CurFn->LastFileId;
else
FileId = CurFn->LastFileId = maybeRecordFile(DL->getFile());
CurFn->LastLoc = DL;
PrevInstLoc = DL;
unsigned FuncId = CurFn->FuncId;
if (const DILocation *SiteLoc = DL->getInlinedAt()) {
@ -2150,9 +2150,23 @@ void CodeViewDebug::beginInstruction(const MachineInstr *MI) {
if (!Asm || !CurFn || MI->isDebugValue() ||
MI->getFlag(MachineInstr::FrameSetup))
return;
// 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 == PrevInstLoc || !DL)
if (!DL && MI->getParent() != PrevInstBB) {
for (const auto &NextMI : *MI->getParent()) {
DL = NextMI.getDebugLoc();
if (DL)
break;
}
}
PrevInstBB = MI->getParent();
// If we still don't have a debug location, don't record a location.
if (!DL)
return;
maybeRecordLocation(DL, Asm->MF);
}

1
lib/CodeGen/AsmPrinter/CodeViewDebug.h
View File

@ -118,7 +118,6 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
SmallVector<LocalVariable, 1> Locals;
DebugLoc LastLoc;
const MCSymbol *Begin = nullptr;
const MCSymbol *End = nullptr;
unsigned FuncId = 0;

97
test/DebugInfo/COFF/lines-bb-start.ll Normal file
View File

@ -0,0 +1,97 @@
; RUN: llc -O0 < %s | FileCheck %s
source_filename = "t.c"
target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
target triple = "i386-pc-windows-msvc19.0.24215"
@str_const = internal unnamed_addr constant [4 x i8] c"str\00", align 1
declare i32 @puts(i8*)
; We had a line info quality issue where the LEA for the string constant had no
; location info, so the .cv_loc directive appeared after it. Now we have logic
; that tries to emit the first valid location to the top of each MBB.
define void @lea_str_loc(i1 %cond) !dbg !8 {
entry:
br i1 %cond, label %if.then, label %if.end, !dbg !17
if.then: ; preds = %entry
br label %return, !dbg !18
if.end: ; preds = %entry
%call = call i32 @puts(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @str_const, i32 0, i32 0)), !dbg !19
br label %return, !dbg !20
return: ; preds = %if.end, %if.then
ret void, !dbg !20
}
; The t.c:5 line marker should appear immediately after the BB label.
; CHECK-LABEL: _lea_str_loc:
; CHECK: .cv_loc {{.*}} # t.c:4:5
; CHECK: jmp LBB{{.*}}
; CHECK: LBB0_{{.*}}: # %if.end
; CHECK-NEXT: .cv_loc {{.*}} # t.c:5:3
; CHECK-NEXT: leal _str_const, %[[reg:[^ ]*]]
; CHECK-NEXT: movl %[[reg]], (%esp)
; CHECK-NEXT: calll _puts
define void @instr_no_loc(i1 %cond) !dbg !21 {
entry:
br i1 %cond, label %if.then, label %if.end, !dbg !22
if.then: ; preds = %entry
br label %return, !dbg !23
if.end: ; preds = %entry
call void asm sideeffect "nop", ""()
%call = call i32 @puts(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @str_const, i32 0, i32 0)), !dbg !24
br label %return, !dbg !25
return: ; preds = %if.end, %if.then
ret void, !dbg !25
}
; CHECK-LABEL: _instr_no_loc:
; CHECK: .cv_loc {{.*}} # t.c:4:5
; CHECK: jmp LBB{{.*}}
; CHECK: LBB1_{{.*}}: # %if.end
; CHECK-NEXT: .cv_loc {{.*}} # t.c:5:3
; CHECK-NEXT: #APP
; CHECK-NEXT: nop
; CHECK-NEXT: #NO_APP
; CHECK-NEXT: leal _str_const, %[[reg:[^ ]*]]
; CHECK-NEXT: movl %[[reg]], (%esp)
; CHECK-NEXT: calll _puts
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5, !6}
!llvm.ident = !{!7}
!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 5.0.0 ", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
!1 = !DIFile(filename: "t.c", directory: "C:\5Csrc\5Cllvm-project\5Cbuild", checksumkind: CSK_MD5, checksum: "b32df088e991f1996b4e4deb3855c14b")
!2 = !{}
!3 = !{i32 1, !"NumRegisterParameters", i32 0}
!4 = !{i32 2, !"CodeView", i32 1}
!5 = !{i32 2, !"Debug Info Version", i32 3}
!6 = !{i32 1, !"wchar_size", i32 2}
!7 = !{!"clang version 5.0.0 "}
!8 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 2, type: !9, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
!9 = !DISubroutineType(types: !10)
!10 = !{null, !11}
!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!13 = !DIExpression()
!14 = !DILocation(line: 2, column: 12, scope: !8)
!15 = !DILocation(line: 3, column: 7, scope: !16)
!16 = distinct !DILexicalBlock(scope: !8, file: !1, line: 3, column: 7)
!17 = !DILocation(line: 3, column: 7, scope: !8)
!18 = !DILocation(line: 4, column: 5, scope: !16)
!19 = !DILocation(line: 5, column: 3, scope: !8)
!20 = !DILocation(line: 6, column: 1, scope: !8)
!21 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 2, type: !9, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
!22 = !DILocation(line: 3, column: 7, scope: !21)
!23 = !DILocation(line: 4, column: 5, scope: !21)
!24 = !DILocation(line: 5, column: 3, scope: !21)
!25 = !DILocation(line: 6, column: 1, scope: !21)

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

@ -193,7 +193,7 @@
; OBJ: ChangeLineOffset: 1
; OBJ: ChangeCodeOffset: 0x35
; OBJ: ChangeCodeOffsetAndLineOffset: {CodeOffset: 0xD, LineOffset: 1}
; OBJ: ChangeCodeLength: 0xF
; OBJ: ChangeCodeLength: 0xA
; OBJ: ]
; OBJ: }
; OBJ: Local {