[DebugInfo] Fix faulty DIExpression::appendToStack assert

[dstenb]

The appendToStack() function asserts that no DW_OP_stack_value or
DW_OP_LLVM_fragment operations are present in the operations to be
appended. The function did that by iterating over all elements in the
array rather than just the operations, leading it to falsely asserting
on the following input produced by getExt(), since 159 (0x9f) is the
DWARF code for DW_OP_stack_value:

{dwarf::DW_OP_LLVM_convert, 159, dwarf::DW_ATE_signed}

Fix this by using expr_op iterators.

[llvmbot]

@llvm/pr-subscribers-debuginfo

@llvm/pr-subscribers-llvm-ir

Author: David Stenberg (dstenb)

Changes

The appendToStack() function asserts that no DW_OP_stack_value or
DW_OP_LLVM_fragment operations are present in the operations to be
appended. The function did that by iterating over all elements in the
array rather than just the operations, leading it to falsely asserting
on the following input produced by getExt(), since 159 (0x9f) is the
DWARF code for DW_OP_stack_value:

{dwarf::DW_OP_LLVM_convert, 159, dwarf::DW_ATE_signed}

Fix this by using expr_op iterators.

---

Full diff: https://github.com/llvm/llvm-project/pull/85255.diff

2 Files Affected:

• (modified) llvm/lib/IR/DebugInfoMetadata.cpp (+6-5)
• (added) llvm/test/DebugInfo/Generic/append-to-stack-assert.ll (+49)

diff --git a/llvm/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
index 28f96653d815b5..f37add2120f13b 100644
--- a/llvm/lib/IR/DebugInfoMetadata.cpp
+++ b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -1880,11 +1880,12 @@ DIExpression *DIExpression::append(const DIExpression *Expr,
 DIExpression *DIExpression::appendToStack(const DIExpression *Expr,
                                           ArrayRef<uint64_t> Ops) {
   assert(Expr && !Ops.empty() && "Can't append ops to this expression");
-  assert(none_of(Ops,
-                 [](uint64_t Op) {
-                   return Op == dwarf::DW_OP_stack_value ||
-                          Op == dwarf::DW_OP_LLVM_fragment;
-                 }) &&
+  assert(std::none_of(expr_op_iterator(Ops.begin()),
+                      expr_op_iterator(Ops.end()),
+                      [](auto Op) {
+                        return Op.getOp() == dwarf::DW_OP_stack_value ||
+                               Op.getOp() == dwarf::DW_OP_LLVM_fragment;
+                      }) &&
          "Can't append this op");
 
   // Append a DW_OP_deref after Expr's current op list if it's non-empty and
diff --git a/llvm/test/DebugInfo/Generic/append-to-stack-assert.ll b/llvm/test/DebugInfo/Generic/append-to-stack-assert.ll
new file mode 100644
index 00000000000000..0c0677f782aa64
--- /dev/null
+++ b/llvm/test/DebugInfo/Generic/append-to-stack-assert.ll
@@ -0,0 +1,49 @@
+; RUN: opt -passes=instcombine -S < %s | FileCheck %s
+
+@f = dso_local local_unnamed_addr global i16 0, align 1, !dbg !0
+@e = dso_local local_unnamed_addr global i159 0, align 1, !dbg !5
+
+; Function Attrs: nounwind
+define dso_local void @g() local_unnamed_addr #0 !dbg !14 {
+; CHECK:    [[TMP0:%.*]] = load i16, ptr @f, align 1
+; CHECK:    [[CONV1:%.*]] = sext i16 [[TMP0]] to i159
+; CHECK:    tail call void @llvm.dbg.value(metadata i159 [[CONV1]], metadata {{![0-9]+}}, metadata !DIExpression(DW_OP_LLVM_convert, 159, DW_ATE_signed, DW_OP_LLVM_convert, 256, DW_ATE_signed, DW_OP_stack_value))
+entry:
+  %0 = load i16, ptr @f, align 1, !dbg !21
+  %conv = sext i16 %0 to i256, !dbg !21
+  tail call void @llvm.dbg.value(metadata i256 %conv, metadata !18, metadata !DIExpression()), !dbg !22
+  %conv1 = trunc i256 %conv to i159, !dbg !23
+  store i159 %conv1, ptr @e, align 1, !dbg !23
+  ret void, !dbg !23
+}
+
+attributes #0 = { nounwind }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!9, !10, !11, !12}
+!llvm.ident = !{!13}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "f", scope: !2, file: !3, line: 7, type: !8, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C11, file: !3, producer: "clang version 19.0.0git", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "bbi-93380.c", directory: "/")
+!4 = !{!0, !5}
+!5 = !DIGlobalVariableExpression(var: !6, expr: !DIExpression())
+!6 = distinct !DIGlobalVariable(name: "e", scope: !2, file: !3, line: 8, type: !7, isLocal: false, isDefinition: true)
+!7 = !DIBasicType(name: "_BitInt", size: 160, encoding: DW_ATE_signed)
+!8 = !DIBasicType(name: "int", size: 16, encoding: DW_ATE_signed)
+!9 = !{i32 7, !"Dwarf Version", i32 4}
+!10 = !{i32 2, !"Debug Info Version", i32 3}
+!11 = !{i32 1, !"wchar_size", i32 1}
+!12 = !{i32 7, !"frame-pointer", i32 2}
+!13 = !{!"clang version 19.0.0git"}
+!14 = distinct !DISubprogram(name: "g", scope: !3, file: !3, line: 9, type: !15, scopeLine: 9, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !17)
+!15 = !DISubroutineType(types: !16)
+!16 = !{null}
+!17 = !{!18}
+!18 = !DILocalVariable(name: "d", scope: !19, file: !3, line: 9, type: !20)
+!19 = distinct !DILexicalBlock(scope: !14, file: !3, line: 9)
+!20 = !DIBasicType(name: "_BitInt", size: 256, encoding: DW_ATE_signed)
+!21 = !DILocation(line: 9, scope: !19)
+!22 = !DILocation(line: 0, scope: !19)
+!23 = !DILocation(line: 9, scope: !14)

[OCHyams]

Ah, nice find. LGTM, thanks.

[felipepiovezan]

An instcombine test in order to test a change to DIEExpression::append operation feels like the wrong granularity. Not to mention this test could start failing for other reasons in the future.

Suggestion: could you have a look at unittests and check if you can build a DIEExpression manually there, and then call appendToStack?

[OCHyams]

+1, seems reasonable to explore putting this in a unittest instead

[dstenb]

Sure! I have changed this to a unit test now.

[felipepiovezan]

LGTM! Thanks for improving the test

[dstenb]

Thanks for the reviews!