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[DebugInfo][Dexter] Speculated BB presents illegal variable value to debugger.

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When SimplifyCFG changes the PHI node into a select instruction, the debug information becomes ambiguous. It causes the debugger to display wrong variable value. 

Differential Revision: https://reviews.llvm.org/D51976

llvm-svn: 342527
This commit is contained in:
Carlos Alberto Enciso 2018-09-19 08:16:56 +00:00
parent 179d7c06a6
commit 2085f61d99
4 changed files with 119 additions and 2 deletions
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3
include/llvm/Transforms/Utils/Local.h
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@ -443,6 +443,9 @@ void copyNonnullMetadata(const LoadInst &OldLI, MDNode *N, LoadInst &NewLI);
void copyRangeMetadata(const DataLayout &DL, const LoadInst &OldLI, MDNode *N,
LoadInst &NewLI);
/// Remove the debug intrinsic instructions for the given instruction.
void dropDebugUsers(Instruction &I);
//===----------------------------------------------------------------------===//
// Intrinsic pattern matching
//

7
lib/Transforms/Utils/Local.cpp
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@ -2522,6 +2522,13 @@ void llvm::copyRangeMetadata(const DataLayout &DL, const LoadInst &OldLI,
}
}
void llvm::dropDebugUsers(Instruction &I) {
SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
findDbgUsers(DbgUsers, &I);
for (auto *DII : DbgUsers)
DII->eraseFromParent();
}
namespace {
/// A potential constituent of a bitreverse or bswap expression. See

8
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -2370,15 +2370,19 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
// Move all 'aggressive' instructions, which are defined in the
// conditional parts of the if's up to the dominating block.
if (IfBlock1) {
for (auto &I : *IfBlock1)
for (auto &I : *IfBlock1) {
I.dropUnknownNonDebugMetadata();
dropDebugUsers(I);
}
DomBlock->getInstList().splice(InsertPt->getIterator(),
IfBlock1->getInstList(), IfBlock1->begin(),
IfBlock1->getTerminator()->getIterator());
}
if (IfBlock2) {
for (auto &I : *IfBlock2)
for (auto &I : *IfBlock2) {
I.dropUnknownNonDebugMetadata();
dropDebugUsers(I);
}
DomBlock->getInstList().splice(InsertPt->getIterator(),
IfBlock2->getInstList(), IfBlock2->begin(),
IfBlock2->getTerminator()->getIterator());

103
test/CodeGen/X86/pr38763.ll Normal file
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@ -0,0 +1,103 @@
; RUN: opt < %s -S -simplifycfg | FileCheck %s
; When SimplifyCFG changes the PHI node into a select instruction, the debug
; information becomes ambiguous. It causes the debugger to display wrong
; variable value.
;
; When in the debugger, on the line "if (read == 4)", the value of "result"
; is reported as '2', where it should be zero.
; IR generated with:
; clang -S -g -O2 -emit-llvm pr38763.cpp -o pr38763.ll -mllvm -opt-bisect-limit=10
; // pr38763.cpp
; int main() {
; volatile int foo = 4;
; int read = foo;
; int read1 = foo;
;
; int result = 0;
; if (read == 4) {
; result = read1 + 2;
; } else {
; result = read1 - 2;
; }
;
; return result;
; }
; Remove the '@llvm.dbg.value' associated with 'result' for the true/false
; branches, as they becomes ambiguous.
; CHECK-LABEL: entry
; CHECK: %cmp = icmp eq i32 %foo.0., 4
; CHECK: %add = add nsw i32 %foo.0.4, 2, !dbg !18
; CHECK-NOT: @llvm.dbg.value(metadata i32 %add
; CHECK: %sub = add nsw i32 %foo.0.4, -2, !dbg !21
; CHECK-NOT: @llvm.dbg.value(metadata i32 %sub
; CHECK: %result.0 = select i1 %cmp, i32 %add, i32 %sub
; CHECK: call void @llvm.dbg.value(metadata i32 %result.0, metadata !12, metadata !DIExpression()), !dbg !17
; ModuleID = 'pr38763.cpp'
source_filename = "pr38763.cpp"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"
; Function Attrs: norecurse nounwind uwtable
define dso_local i32 @main() local_unnamed_addr #0 !dbg !7 {
entry:
%foo = alloca i32, align 4
%foo.0..sroa_cast = bitcast i32* %foo to i8*
store volatile i32 4, i32* %foo, align 4, !tbaa !19
%foo.0. = load volatile i32, i32* %foo, align 4
%foo.0.4 = load volatile i32, i32* %foo, align 4
call void @llvm.dbg.value(metadata i32 0, metadata !16, metadata !DIExpression()), !dbg !27
%cmp = icmp eq i32 %foo.0., 4
br i1 %cmp, label %if.then, label %if.else
if.then: ; preds = %entry
%add = add nsw i32 %foo.0.4, 2, !dbg !31
call void @llvm.dbg.value(metadata i32 %add, metadata !16, metadata !DIExpression()), !dbg !27
br label %if.end
if.else: ; preds = %entry
%sub = add nsw i32 %foo.0.4, -2, !dbg !34
call void @llvm.dbg.value(metadata i32 %sub, metadata !16, metadata !DIExpression()), !dbg !27
br label %if.end
if.end: ; preds = %if.else, %if.then
%result.0 = phi i32 [ %add, %if.then ], [ %sub, %if.else ]
call void @llvm.dbg.value(metadata i32 %result.0, metadata !16, metadata !DIExpression()), !dbg !27
ret i32 %result.0
}
; Function Attrs: nounwind readnone speculatable
declare void @llvm.dbg.value(metadata, metadata, metadata) #2
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5}
!llvm.ident = !{!6}
!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 8.0.0 (trunk 342209)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
!1 = !DIFile(filename: "pr38763.cpp", directory: ".")
!2 = !{}
!3 = !{i32 2, !"Dwarf Version", i32 4}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = !{i32 1, !"wchar_size", i32 4}
!6 = !{!"clang version 8.0.0 (trunk 342209)"}
!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !11)
!8 = !DISubroutineType(types: !9)
!9 = !{!10}
!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!11 = !{!16}
!16 = !DILocalVariable(name: "result", scope: !7, file: !1, line: 6, type: !10)
!19 = !{!20, !20, i64 0}
!20 = !{!"int", !21, i64 0}
!21 = !{!"omnipotent char", !22, i64 0}
!22 = !{!"Simple C++ TBAA"}
!27 = !DILocation(line: 6, column: 7, scope: !7)
!29 = distinct !DILexicalBlock(scope: !7, file: !1, line: 7, column: 7)
!31 = !DILocation(line: 8, column: 20, scope: !32)
!32 = distinct !DILexicalBlock(scope: !29, file: !1, line: 7, column: 18)
!34 = !DILocation(line: 10, column: 20, scope: !35)
!35 = distinct !DILexicalBlock(scope: !29, file: !1, line: 9, column: 10)