[DebugInfo] [SelectionDAG] Fix handling of duplicate dbg values

[Snowy1803]

Before this fix, a duplicate llvm.dbg.value intrinsic referring to an argument, after an alloca, would be generated with $noreg, losing debug information. Instead, we silently drop the second debug info, so it doesn't break the first one.

rdar://125375717

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[llvmbot]

@llvm/pr-subscribers-llvm-selectiondag

@llvm/pr-subscribers-debuginfo

Author: Emil Pedersen (Snowy1803)

Changes

Before this fix, a duplicate llvm.dbg.value intrinsic referring to an argument, after an alloca, would be generated with $noreg, losing debug information. Instead, we silently drop the second debug info, so it doesn't break the first one.

rdar://125375717

---

Full diff: https://github.com/llvm/llvm-project/pull/86598.diff

2 Files Affected:

• (modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (+1-1)
• (added) llvm/test/DebugInfo/X86/dbg-value-funcarg-duplicates.ll (+66)

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 84df98b8a613cc..9ded2bce39d37a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -6011,7 +6011,7 @@ bool SelectionDAGBuilder::EmitFuncArgumentDbgValue(
       if (ArgNo >= FuncInfo.DescribedArgs.size())
         FuncInfo.DescribedArgs.resize(ArgNo + 1, false);
       else if (!IsInPrologue && FuncInfo.DescribedArgs.test(ArgNo))
-        return false;
+        return !NodeMap[V].getNode();
       FuncInfo.DescribedArgs.set(ArgNo);
     }
   }
diff --git a/llvm/test/DebugInfo/X86/dbg-value-funcarg-duplicates.ll b/llvm/test/DebugInfo/X86/dbg-value-funcarg-duplicates.ll
new file mode 100644
index 00000000000000..a4d6b0aa3724b1
--- /dev/null
+++ b/llvm/test/DebugInfo/X86/dbg-value-funcarg-duplicates.ll
@@ -0,0 +1,66 @@
+; RUN: llc -mtriple=x86_64-unknown-linux-gnu -start-after=codegenprepare -stop-before=finalize-isel -o - bugpoint-reduced-simplified.ll -experimental-debug-variable-locations=false | FileCheck %s
+
+; Input to this test was created by reducing a Swift file using bugpoint
+
+; CHECK-DAG: ![[LHS:.*]] = !DILocalVariable(name: "lhs"
+
+define hidden i64 @"_wideDivide42"(ptr %0, ptr %1, ptr %2, i64 %3, i64 %4, i64 %5, i64 %6, i64 %7, i64 %8) local_unnamed_addr !dbg !16 {
+; CHECK-LABEL: name:            _wideDivide42
+; CHECK-NOT:  DBG_VALUE
+; CHECK:      DBG_VALUE $rcx, $noreg, ![[LHS]], !DIExpression(DW_OP_LLVM_fragment, 0, 64)
+; CHECK-NEXT: DBG_VALUE $r8, $noreg, ![[LHS]], !DIExpression(DW_OP_LLVM_fragment, 64, 64)
+; CHECK-NEXT: DBG_VALUE $r9, $noreg, ![[LHS]], !DIExpression(DW_OP_LLVM_fragment, 128, 64)
+; CHECK-NEXT: DBG_VALUE %fixed-stack.{{.+}}, ![[LHS]], !DIExpression(DW_OP_LLVM_fragment, 192, 64)
+; The duplicates should be removed:
+; CHECK-NOT:  DBG_VALUE
+
+entry:
+  %9 = alloca i64, align 8
+  call void @llvm.dbg.value(metadata i64 %3, metadata !24, metadata !DIExpression(DW_OP_LLVM_fragment, 0, 64)), !dbg !67
+  call void @llvm.dbg.value(metadata i64 %4, metadata !24, metadata !DIExpression(DW_OP_LLVM_fragment, 64, 64)), !dbg !67
+  call void @llvm.dbg.value(metadata i64 %3, metadata !24, metadata !DIExpression(DW_OP_LLVM_fragment, 0, 64)), !dbg !67
+  call void @llvm.dbg.value(metadata i64 %4, metadata !24, metadata !DIExpression(DW_OP_LLVM_fragment, 64, 64)), !dbg !67
+  call void @llvm.dbg.value(metadata i64 %5, metadata !24, metadata !DIExpression(DW_OP_LLVM_fragment, 128, 64)), !dbg !67
+  call void @llvm.dbg.value(metadata i64 %6, metadata !24, metadata !DIExpression(DW_OP_LLVM_fragment, 192, 64)), !dbg !67
+  br i1 poison, label %11, label %10, !dbg !68, !prof !69
+
+10:                                               ; preds = %entry
+  tail call void asm sideeffect "", "n"(i32 7) #7
+  unreachable
+
+11:                                               ; preds = %entry
+  tail call void @abort()
+  unreachable
+}
+
+declare void @abort()
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+attributes #7 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!13}
+!llvm.linker.options = !{!14, !15}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_Swift, file: !1, producer: "Swift", isOptimized: true, runtimeVersion: 6, emissionKind: FullDebug)
+!1 = !DIFile(filename: "Int128.swift", directory: "")
+!13 = !{i32 2, !"Debug Info Version", i32 3}
+!14 = !{!"-lswiftCore"}
+!15 = !{!"-lobjc"}
+!16 = distinct !DISubprogram(name: "_wideDivide42", scope: !0, file: !1, line: 222, type: !17, scopeLine: 222, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !23)
+!17 = !DISubroutineType(types: !18)
+!18 = !{!19, !20, !20, !20, !20, !20, !20}
+!19 = !DICompositeType(tag: DW_TAG_structure_type, name: "4 x UInt64", flags: DIFlagFwdDecl, runtimeLang: DW_LANG_Swift)
+!20 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "UInt64", scope: !1, file: !1, size: 64, elements: !22, runtimeLang: DW_LANG_Swift)
+!22 = !{}
+!23 = !{!24, !27}
+!24 = !DILocalVariable(name: "lhs", arg: 1, scope: !16, file: !1, line: 223, type: !25, flags: DIFlagArtificial)
+!25 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !26)
+!26 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "2 x 2 x UInt64", file: !1, size: 256, elements: !22, runtimeLang: DW_LANG_Swift)
+!27 = !DILocalVariable(name: "rhs", arg: 2, scope: !16, file: !1, line: 223, type: !28, flags: DIFlagArtificial)
+!28 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !29)
+!29 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "2 x UInt64", file: !1, size: 128, elements: !22, runtimeLang: DW_LANG_Swift)
+!67 = !DILocation(line: 0, scope: !16)
+!68 = !DILocation(line: 225, column: 9, scope: !16)
+!69 = !{!"branch_weights", i32 1, i32 2000}

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