[PATCH] D82062: [SimplifyCFG] Update debug location when folding branch to common destination
Davide Italiano via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Wed Jun 17 17:17:30 PDT 2020
davide created this revision.
davide added reviewers: vsk, aprantl, jmorse.
Herald added subscribers: kosarev, hiraditya.
Herald added a project: LLVM.
davide updated this revision to Diff 271527.
davide added a comment.
Correct diff.
Fixes https://bugs.llvm.org/show_bug.cgi?id=46008
SimplifyCFG flattens the CFG transforming:
@a = local_unnamed_addr global i16 1, align 2, !dbg !0
@c = local_unnamed_addr global i32 0, align 4, !dbg !9
@b = local_unnamed_addr global i32 0, align 4, !dbg !6
; Function Attrs: nounwind ssp uwtable
define void @d() #0 !dbg !17 {
ret void, !dbg !20
}
; Function Attrs: nounwind ssp uwtable
define i32 @main() local_unnamed_addr #0 !dbg !21 {
call void @llvm.dbg.value(metadata i32* @c, metadata !25, metadata !DIExpression()), !dbg !27
br label %1, !dbg !28
1: ; preds = %7, %0
%2 = load i16, i16* @a, align 2, !dbg !29, !tbaa !32
%3 = icmp slt i16 %2, 1, !dbg !36
br i1 %3, label %4, label %8, !dbg !37
4: ; preds = %1
%5 = load i32, i32* @c, align 4, !dbg !38, !tbaa !40
%6 = icmp eq i32 %5, 0, !dbg !42
br i1 %6, label %7, label %8, !dbg !43
7: ; preds = %4
store i16 ptrtoint (void ()* @d to i16), i16* @a, align 2, !dbg !44, !tbaa !32
br label %1, !dbg !45, !llvm.loop !46
8: ; preds = %4, %1
%9 = load i32, i32* @c, align 4, !dbg !49, !tbaa !40
store i32 %9, i32* @b, align 4, !dbg !50, !tbaa !40
ret i32 0, !dbg !51
}
into
; Function Attrs: nounwind ssp uwtable
define i32 @main() local_unnamed_addr #0 !dbg !21 {
call void @llvm.dbg.value(metadata i32* @c, metadata !25, metadata !DIExpression()), !dbg !27
br label %1, !dbg !28
1: ; preds = %6, %0
%2 = load i16, i16* @a, align 2, !dbg !29, !tbaa !32
%3 = icmp slt i16 %2, 1, !dbg !36
%4 = load i32, i32* @c, align 4, !dbg !37
%5 = icmp eq i32 %4, 0, !dbg !39
%or.cond = and i1 %3, %5, !dbg !40
br i1 %or.cond, label %6, label %7, !dbg !40
6: ; preds = %1
store i16 ptrtoint (void ()* @d to i16), i16* @a, align 2, !dbg !41, !tbaa !32
br label %1, !dbg !42, !llvm.loop !43
7: ; preds = %1
%8 = load i32, i32* @c, align 4, !dbg !46, !tbaa !47
store i32 %8, i32* @b, align 4, !dbg !49, !tbaa !47
ret i32 0, !dbg !50
}
When the instructions get folded, 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
https://reviews.llvm.org/D82062
Files:
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
llvm/test/Transforms/SimplifyCFG/basictest.ll
llvm/test/Transforms/SimplifyCFG/fold-debug-location.ll
Index: llvm/test/Transforms/SimplifyCFG/fold-debug-location.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/SimplifyCFG/fold-debug-location.ll
@@ -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)
Index: llvm/test/Transforms/SimplifyCFG/basictest.ll
===================================================================
--- llvm/test/Transforms/SimplifyCFG/basictest.ll
+++ llvm/test/Transforms/SimplifyCFG/basictest.ll
@@ -98,7 +98,7 @@
; 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
Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2776,6 +2776,12 @@
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 @@
// 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);
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