[llvm] [SelectionDAG] Salvage debug info for non-constant ADDs (PR #68981)

[via llvm-commits]

================
@@ -0,0 +1,60 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 3
+# RUN: llc -mtriple=sparcv9 %s -start-before=sparc-isel -o - -stop-after=sparc-isel | FileCheck %s
+--- |
+  target datalayout = "E-m:e-i64:64-n32:64-S128"
+  target triple = "sparcv9"
+
+  define void @pointer_add_unknown_offset(ptr %base, i32 %offset) !dbg !7 {
+  entry:
+    %idx.ext = sext i32 %offset to i64
+    %add.ptr = getelementptr inbounds i32, ptr %base, i64 %idx.ext
+    call void @llvm.dbg.value(metadata ptr %add.ptr, metadata !13, metadata !DIExpression()), !dbg !16
+    call void @llvm.dbg.value(metadata ptr %add.ptr, metadata !14, metadata !DIExpression(DW_OP_plus_uconst, 3, DW_OP_stack_value)), !dbg !16
+    call void @llvm.dbg.value(metadata !DIArgList(ptr %add.ptr, ptr %add.ptr), metadata !15, metadata !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus)), !dbg !16
+    store i32 42, ptr %add.ptr, align 4
+    ret void
+  }
+
+  declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!2, !3, !4, !5}
+  !llvm.ident = !{!6}
+
+  !0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+  !1 = !DIFile(filename: "test.c", directory: "/tmp", checksumkind: CSK_MD5, checksum: "4321633e52cefeee6e307c697a82574f")
+  !2 = !{i32 7, !"Dwarf Version", i32 5}
+  !3 = !{i32 2, !"Debug Info Version", i32 3}
+  !4 = !{i32 1, !"wchar_size", i32 4}
+  !5 = !{i32 7, !"debug-info-assignment-tracking", i1 true}
+  !6 = !{!"clang"}
+  !7 = distinct !DISubprogram(name: "pointer_add_unknown_offset", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !12)
+  !8 = !DISubroutineType(types: !9)
+  !9 = !{null, !10, !11}
+  !10 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !11, size: 64)
+  !11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !12 = !{!13, !14, !15}
+  !13 = !DILocalVariable(name: "p", scope: !7, file: !1, line: 2, type: !10)
+  !14 = !DILocalVariable(name: "q", scope: !7, file: !1, line: 2, type: !10)
+  !15 = !DILocalVariable(name: "r", scope: !7, file: !1, line: 2, type: !10)
+  !16 = !DILocation(line: 0, scope: !7)
+...
+---
+name:            pointer_add_unknown_offset
+alignment:       4
+tracksRegLiveness: true
+body:             |
+  ; CHECK-LABEL: name: pointer_add_unknown_offset
+  ; CHECK: bb.0.entry:
+  ; CHECK-NEXT:   liveins: $i0, $i1
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:i64regs = COPY $i1
+  ; CHECK-NEXT:   [[COPY1:%[0-9]+]]:i64regs = COPY $i0
+  ; CHECK-NEXT:   [[SRAri:%[0-9]+]]:i64regs = SRAri [[COPY]], 0
+  ; CHECK-NEXT:   [[SLLXri:%[0-9]+]]:i64regs = SLLXri killed [[SRAri]], 2
+  ; CHECK-NEXT:   DBG_VALUE_LIST !13, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_stack_value), [[COPY1]], [[SLLXri]], debug-location !16
+  ; CHECK-NEXT:   DBG_VALUE_LIST !14, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_plus_uconst, 3, DW_OP_stack_value), [[COPY1]], [[SLLXri]], debug-location !16
+  ; CHECK-NEXT:   DBG_VALUE_LIST !15, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 2, DW_OP_plus, DW_OP_LLVM_arg, 1, DW_OP_LLVM_arg, 3, DW_OP_plus, DW_OP_plus, DW_OP_stack_value), [[COPY1]], [[COPY1]], [[SLLXri]], [[SLLXri]], debug-location !16
----------------
dstenb wrote:

Yes, the debug values for "p" and "q" are still non-variadic when entering `SelectionDAG::salvageDebugInfo()`:

```
 DbgVal(Order=3)(SDNODE=t9:0):"p"
 DbgVal(Order=3)(SDNODE=t9:0):"q"!DIExpression(DW_OP_plus_uconst, 3, DW_OP_stack_value)
```

https://github.com/llvm/llvm-project/pull/68981