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[SimplifyCFG] Update debug location when folding branch to common destination

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Sometimes a dead block gets folded and the debug information is still
retained. This manifests as jumpy stepping in lldb, see the bugzilla PR
for an end-to-end C testcase.

Fixes https://bugs.llvm.org/show_bug.cgi?id=46008

Differential Revision:  https://reviews.llvm.org/D82062
This commit is contained in:
Davide Italiano 2020-06-18 12:33:02 -07:00
parent 65e6138f5b
commit f3c25b4ad7
3 changed files with 59 additions and 1 deletions
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11
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -2776,6 +2776,12 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI, MemorySSAUpdater *MSSAU,
if (isa<DbgInfoIntrinsic>(BonusInst))
continue;
Instruction *NewBonusInst = BonusInst->clone();
// When we fold the bonus instructions we want to make sure we
// reset their debug locations in order to avoid stepping on dead
// code caused by folding dead branches.
NewBonusInst->setDebugLoc(DebugLoc());
RemapInstruction(NewBonusInst, VMap,
RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
VMap[&*BonusInst] = NewBonusInst;
@ -2795,6 +2801,11 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI, MemorySSAUpdater *MSSAU,
// Clone Cond into the predecessor basic block, and or/and the
// two conditions together.
Instruction *CondInPred = Cond->clone();
// Reset the condition debug location to avoid jumping on dead code
// as the result of folding dead branches.
CondInPred->setDebugLoc(DebugLoc());
RemapInstruction(CondInPred, VMap,
RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
PredBlock->getInstList().insert(PBI->getIterator(), CondInPred);

2
test/Transforms/SimplifyCFG/basictest.ll
View File

@ -98,7 +98,7 @@ define i8 @test6f() {
; CHECK: alloca i8, align 1
; CHECK-NEXT: call i8 @test6g
; CHECK-NEXT: icmp eq i8 %tmp, 0
; CHECK-NEXT: load i8, i8* %r, align 1, !dbg !{{[0-9]+$}}
; CHECK-NEXT: load i8, i8* %r, align 1{{$}}
bb0:
%r = alloca i8, align 1

47
test/Transforms/SimplifyCFG/fold-debug-location.ll Normal file
View File

@ -0,0 +1,47 @@
; RUN: opt -S -simplifycfg < %s | FileCheck %s --match-full-lines
; Make sure we reset the debug location when folding instructions.
; CHECK: [[VAL:%.*]] = and i32 %c2, %k
; CHECK-NEXT: [[VAL2:%.*]] icmp eq i32 [[VAL]], 0
declare i32 @bar(...)
define i32 @patatino(i32 %k, i32 %c1, i32 %c2) !dbg !6 {
%1 = and i32 %c1, %k, !dbg !8
%2 = icmp eq i32 %1, 0, !dbg !9
br i1 %2, label %8, label %3, !dbg !10
3:
%4 = and i32 %c2, %k, !dbg !11
%5 = icmp eq i32 %4, 0, !dbg !12
br i1 %5, label %8, label %6, !dbg !13
6:
%7 = tail call i32 (...) @bar(), !dbg !14
br label %8, !dbg !15
8:
ret i32 undef, !dbg !16
}
!llvm.dbg.cu = !{!0}
!llvm.debugify = !{!3, !4}
!llvm.module.flags = !{!5}
!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
!1 = !DIFile(filename: "a.ll", directory: "/")
!2 = !{}
!3 = !{i32 9}
!4 = !{i32 0}
!5 = !{i32 2, !"Debug Info Version", i32 3}
!6 = distinct !DISubprogram(name: "patatino", linkageName: "patatino", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
!7 = !DISubroutineType(types: !2)
!8 = !DILocation(line: 1, column: 1, scope: !6)
!9 = !DILocation(line: 2, column: 1, scope: !6)
!10 = !DILocation(line: 3, column: 1, scope: !6)
!11 = !DILocation(line: 4, column: 1, scope: !6)
!12 = !DILocation(line: 5, column: 1, scope: !6)
!13 = !DILocation(line: 6, column: 1, scope: !6)
!14 = !DILocation(line: 7, column: 1, scope: !6)
!15 = !DILocation(line: 8, column: 1, scope: !6)
!16 = !DILocation(line: 9, column: 1, scope: !6)