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[DebugInfo][Dexter] Unreachable line stepped onto after SimplifyCFG.

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When SimplifyCFG changes the PHI node into a select instruction, the debug line records becomes ambiguous. It causes the debugger to display unreachable source lines. 

Differential Revision: https://reviews.llvm.org/D52887

llvm-svn: 344120
This commit is contained in:
Carlos Alberto Enciso 2018-10-10 08:29:55 +00:00
parent 90a3c6f55a
commit e0f56f3bb6
5 changed files with 151 additions and 29 deletions
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9
include/llvm/Transforms/Utils/Local.h
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@ -446,6 +446,15 @@ void copyRangeMetadata(const DataLayout &DL, const LoadInst &OldLI, MDNode *N,
/// Remove the debug intrinsic instructions for the given instruction.
void dropDebugUsers(Instruction &I);
/// Hoist all of the instructions in the \p IfBlock to the dominant block
/// \p DomBlock, by moving its instructions to the insertion point \p InsertPt.
///
/// The moved instructions receive the insertion point debug location values
/// (DILocations) and their debug intrinsic instructions (dbg.values) are
/// removed.
void hoistAllInstructionsInto(BasicBlock *DomBlock,Instruction *InsertPt,
BasicBlock *IfBlock);
//===----------------------------------------------------------------------===//
// Intrinsic pattern matching
//

28
lib/Transforms/Utils/Local.cpp
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@ -2529,6 +2529,34 @@ void llvm::dropDebugUsers(Instruction &I) {
DII->eraseFromParent();
}
void llvm::hoistAllInstructionsInto(BasicBlock *DomBlock,Instruction *InsertPt,
BasicBlock *IfBlock) {
// Since we are moving the instructions out of its basic block, we do not
// retain their original debug locations (DILocations) and debug intrinsic
// instructions (dbg.values).
//
// Doing so would degrade the debugging experience and adversely affect the
// accuracy of profiling information.
//
// Currently, when hoisting the instructions, we take the following actions:
// - Remove their dbg.values.
// - Set their debug locations to the values from the insertion point.
//
// See PR38762 for more details.
//
// TODO: Extend llvm.dbg.value to take more than one SSA Value (PR39141) to
// encode predicated DIExpressions that yield different results on different
// code paths.
for (auto &I : *IfBlock) {
I.dropUnknownNonDebugMetadata();
dropDebugUsers(I);
I.setDebugLoc(InsertPt->getDebugLoc());
}
DomBlock->getInstList().splice(InsertPt->getIterator(),
IfBlock->getInstList(), IfBlock->begin(),
IfBlock->getTerminator()->getIterator());
}
namespace {
/// A potential constituent of a bitreverse or bswap expression. See

22
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -2375,24 +2375,10 @@ 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) {
I.dropUnknownNonDebugMetadata();
dropDebugUsers(I);
}
DomBlock->getInstList().splice(InsertPt->getIterator(),
IfBlock1->getInstList(), IfBlock1->begin(),
IfBlock1->getTerminator()->getIterator());
}
if (IfBlock2) {
for (auto &I : *IfBlock2) {
I.dropUnknownNonDebugMetadata();
dropDebugUsers(I);
}
DomBlock->getInstList().splice(InsertPt->getIterator(),
IfBlock2->getInstList(), IfBlock2->begin(),
IfBlock2->getTerminator()->getIterator());
}
if (IfBlock1)
hoistAllInstructionsInto(DomBlock, InsertPt, IfBlock1);
if (IfBlock2)
hoistAllInstructionsInto(DomBlock, InsertPt, IfBlock2);
while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
// Change the PHI node into a select instruction.

101
test/CodeGen/X86/pr38762.ll Normal file
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@ -0,0 +1,101 @@
; RUN: opt < %s -S -simplifycfg | FileCheck %s
; Note: This patch is a complement to pr38763.
;
; When SimplifyCFG changes the PHI node into a select instruction, the debug
; information becomes ambiguous. It causes the debugger to display unreached
; lines and invalid variable values.
;
; When in the debugger, on the line "if (read1 > 3)", and we step from the
; 'if' condition, onto the addition, then back to the 'if' again, which is
; misleading because that addition doesn't really "happen" (it's speculated).
; IR generated with:
; clang -S -g -gno-column-info -O2 -emit-llvm pr38762.cpp -o pr38762.ll -mllvm -opt-bisect-limit=10
; // pr38762.cpp
; int main() {
; volatile int foo = 0;
; int read1 = foo;
; int brains = foo;
;
; if (read1 > 3) {
; brains *= 2;
; brains += 1;
; }
;
; return brains;
; }
; Change the debug locations associated with the PHI nodes being promoted, to
; the debug locations from the insertion point in the dominant block.
; CHECK-LABEL: entry
; CHECK: %cmp = icmp sgt i32 %foo.0., 3, !dbg !14
; CHECK: %mul = shl nsw i32 %foo.0.5, 1, !dbg !16
; CHECK-NOT: call void @llvm.dbg.value(metadata i32 %mul, metadata !15, metadata !DIExpression()), !dbg !25
; CHECK: %add = or i32 %mul, 1, !dbg !16
; CHECK-NOT: call void @llvm.dbg.value(metadata i32 %add, metadata !15, metadata !DIExpression()), !dbg !25
; CHECK: %brains.0 = select i1 %cmp, i32 %add, i32 %foo.0.5, !dbg !16
; ModuleID = 'pr38762.cpp'
source_filename = "pr38762.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 0, i32* %foo, align 4
%foo.0. = load volatile i32, i32* %foo, align 4
%foo.0.5 = load volatile i32, i32* %foo, align 4
call void @llvm.dbg.value(metadata i32 %foo.0.5, metadata !15, metadata !DIExpression()), !dbg !25
%cmp = icmp sgt i32 %foo.0., 3, !dbg !26
br i1 %cmp, label %if.then, label %if.end, !dbg !28
if.then: ; preds = %entry
%mul = shl nsw i32 %foo.0.5, 1, !dbg !29
call void @llvm.dbg.value(metadata i32 %mul, metadata !15, metadata !DIExpression()), !dbg !25
%add = or i32 %mul, 1, !dbg !31
call void @llvm.dbg.value(metadata i32 %add, metadata !15, metadata !DIExpression()), !dbg !25
br label %if.end, !dbg !32
if.end: ; preds = %if.then, %entry
%brains.0 = phi i32 [ %add, %if.then ], [ %foo.0.5, %entry ], !dbg !33
call void @llvm.dbg.value(metadata i32 %brains.0, metadata !15, metadata !DIExpression()), !dbg !25
ret i32 %brains.0, !dbg !35
}
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 343753)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
!1 = !DIFile(filename: "pr38762.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 343753)"}
!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 = !{!15}
!13 = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: !10)
!15 = !DILocalVariable(name: "brains", scope: !7, file: !1, line: 4, type: !10)
!25 = !DILocation(line: 4, scope: !7)
!26 = !DILocation(line: 6, scope: !27)
!27 = distinct !DILexicalBlock(scope: !7, file: !1, line: 6)
!28 = !DILocation(line: 6, scope: !7)
!29 = !DILocation(line: 7, scope: !30)
!30 = distinct !DILexicalBlock(scope: !27, file: !1, line: 6)
!31 = !DILocation(line: 8, scope: !30)
!32 = !DILocation(line: 9, scope: !30)
!33 = !DILocation(line: 0, scope: !7)
!34 = !DILocation(line: 12, scope: !7)
!35 = !DILocation(line: 11, scope: !7)

20
test/CodeGen/X86/pr38763.ll
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@ -30,13 +30,13 @@
; 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: %cmp = icmp eq i32 %foo.0., 4, !dbg !14
; CHECK: %add = add nsw i32 %foo.0.4, 2, !dbg !16
; CHECK-NOT: @llvm.dbg.value(metadata i32 %add
; CHECK: %sub = add nsw i32 %foo.0.4, -2, !dbg !21
; CHECK: %sub = add nsw i32 %foo.0.4, -2, !dbg !16
; 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
; CHECK: call void @llvm.dbg.value(metadata i32 %result.0, metadata !12, metadata !DIExpression()), !dbg !13
; ModuleID = 'pr38763.cpp'
source_filename = "pr38763.cpp"
@ -48,12 +48,12 @@ 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
store volatile i32 4, i32* %foo, align 4
%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
%cmp = icmp eq i32 %foo.0., 4, !dbg !28
br i1 %cmp, label %if.then, label %if.else, !dbg !30
if.then: ; preds = %entry
%add = add nsw i32 %foo.0.4, 2, !dbg !31
@ -91,12 +91,10 @@ declare void @llvm.dbg.value(metadata, metadata, metadata) #2
!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)
!28 = !DILocation(line: 7, column: 12, scope: !29)
!29 = distinct !DILexicalBlock(scope: !7, file: !1, line: 7, column: 7)
!30 = !DILocation(line: 7, column: 7, scope: !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)