[DebugInfo][Dexter] Speculated BB presents illegal variable value to debugger.
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
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@342527 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/llvm/Transforms/Utils/Local.h b/include/llvm/Transforms/Utils/Local.h
index 8ec689e..f7da696 100644
--- a/include/llvm/Transforms/Utils/Local.h
+++ b/include/llvm/Transforms/Utils/Local.h
@@ -443,6 +443,9 @@
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
//
diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
index c65a0b7..879145c 100644
--- a/lib/Transforms/Utils/Local.cpp
+++ b/lib/Transforms/Utils/Local.cpp
@@ -2522,6 +2522,13 @@
}
}
+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
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 422d1c9..493d168 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2370,15 +2370,19 @@
// 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());
diff --git a/test/CodeGen/X86/pr38763.ll b/test/CodeGen/X86/pr38763.ll
new file mode 100644
index 0000000..b36e1ef
--- /dev/null
+++ b/test/CodeGen/X86/pr38763.ll
@@ -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)
