DAG: Cleanup assertion in EmitFuncArgumentDbgValue

[cdevadas]

Summary

Removing an assertion introduced with D68945. The
patch was later reverted with 6531a78ac4b5, but failed
to remove this assertion. It causes a problem while
trying to split a 64-bit argument into sub registers.

[arsenm]

llvm/test/CodeGen/AMDGPU/sret-arg-dbg-value.ll

5 ↗

(On Diff #341765)

I'm prefer this not use an sret argument since this IR is broken and the verifier should reject it since the pointer has the wrong address space

[cdevadas]

Test re-written with a pointer argument instead of sret arg.

[arsenm]

llvm/test/CodeGen/AMDGPU/ptr-arg-dbg-value.ll

5

Add a comment explaining what this tests

15

Maybe also add a case where the pointer ends up passed in memory, and another where half is in memory and half in a register

[cdevadas]

Added a comment in the lit test.
This test is sufficient to prove that the assertion is really broken.

[cdevadas]

Captured more use cases of pointer argument split between register and memory or argument fully in memory.
Also, put a note for the incomplete/missing Debug value handling for the cases involved with memory.

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

auto splitMultiRegDbgValue = [&](ArrayRef<std::pair<unsigned, TypeSize>>
         // If a valid fragment expression cannot be created, the variable's
         // correct value cannot be determined and so it is set as Undef.
         if (!FragmentExpr) {
           SDDbgValue *SDV = DAG.getConstantDbgValue(
               Variable, Expr, UndefValue::get(V->getType()), DL, SDNodeOrder);
           DAG.AddDbgValue(SDV, false);
           continue;
         }
-        assert(!IsDbgDeclare && "DbgDeclare operand is not in memory?");
         FuncInfo.ArgDbgValues.push_back(
           BuildMI(MF, DL, TII->get(TargetOpcode::DBG_VALUE), IsDbgDeclare,
                   RegAndSize.first, Variable, *FragmentExpr));
       }
     };
 
     // Check if ValueMap has reg number.
     DenseMap<const Value *, Register>::const_iterator

llvm/test/CodeGen/AMDGPU/ptr-arg-dbg-value.ll

+; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx908 < %s | FileCheck %s
+
+; For AMDGPU the 64-bit pointer argument %arg will get split into two registers
+; and for its llvm.dbg.declare, DAG should emit two DBG_VALUE instructions
+; with the fragment expressions.
+
+%struct.A = type { [100 x i32] }
+
+define hidden void @ptr_arg_dbg_value(%struct.A* %arg) #0 !dbg !9 {
+; CHECK-LABEL: ptr_arg_dbg_value:
+; CHECK:    ;DEBUG_VALUE: ptr_arg_dbg_value:a <- [DW_OP_LLVM_fragment 32 32] [$vgpr1+0]
+; CHECK:    ;DEBUG_VALUE: ptr_arg_dbg_value:a <- [DW_OP_LLVM_fragment 0 32] [$vgpr0+0]
+  call void @llvm.dbg.declare(metadata %struct.A* %arg, metadata !20, metadata !DIExpression()), !dbg !21
+  %gep = getelementptr inbounds %struct.A, %struct.A* %arg, i32 0, i32 0, i32 99, !dbg !22
+  store i32 1, i32* %gep, align 4, !dbg !23
+  ret void, !dbg !24
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #0
+
+attributes #0 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6, !7}
+!llvm.ident = !{!8}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 13.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "example.cpp", directory: "temp")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{i32 7, !"uwtable", i32 1}
+!7 = !{i32 7, !"frame-pointer", i32 2}
+!8 = !{!"clang version 13.0.0"}
+!9 = distinct !DISubprogram(name: "ptr_arg_dbg_value", linkageName: "_Z4ptr_arg_dbg_valuev", scope: !10, file: !10, line: 5, type: !11, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!10 = !DIFile(filename: "example.cpp", directory: "temp")
+!11 = !DISubroutineType(types: !12)
+!12 = !{!13}
+!13 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "A", file: !10, line: 1, size: 3200, flags: DIFlagTypePassByValue, elements: !14, identifier: "_ZTS1A")
+!14 = !{!15}
+!15 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !13, file: !10, line: 2, baseType: !16, size: 3200)
+!16 = !DICompositeType(tag: DW_TAG_array_type, baseType: !17, size: 3200, elements: !18)
+!17 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!18 = !{!19}
+!19 = !DISubrange(count: 100)
+!20 = !DILocalVariable(name: "a", scope: !9, file: !10, line: 6, type: !13)
+!21 = !DILocation(line: 6, column: 7, scope: !9)
+!22 = !DILocation(line: 7, column: 7, scope: !9)
+!23 = !DILocation(line: 7, column: 13, scope: !9)
+!24 = !DILocation(line: 8, column: 5, scope: !9)