[DebugInfo][InstrRef] Account for additional indirection from dbg.declares in SelectionDAG

[jmorse]

Summary

Usually dbg.declares get translated into either entries in an MF side-table, or a DBG_VALUE on entry to the function with IsIndirect set (including in instruction referencing mode). Much rarer is a dbg.declare attached to a non-argument value, such as in the test added in this patch where there's a variable-length-array. Such dbg.declares become SDDbgValue nodes with InIndirect=true.

As it happens, we weren't correctly emitting DBG_INSTR_REFs with the additional indirection. This patch adds the extra indirection, encoded as adding an additional DW_OP_deref to the expression. Adds test too.

[Orlando]

LGTM

llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp

 }
 
 MachineInstr *
 InstrEmitter::EmitDbgInstrRef(SDDbgValue *SD,
                               DenseMap<SDValue, Register> &VRBaseMap) {
   assert(!SD->isVariadic());
   SDDbgOperand DbgOperand = SD->getLocationOps()[0];
   MDNode *Var = SD->getVariable();
-  MDNode *Expr = SD->getExpression();
+  DIExpression *Expr = (DIExpression*)SD->getExpression();
   DebugLoc DL = SD->getDebugLoc();
   const MCInstrDesc &RefII = TII->get(TargetOpcode::DBG_INSTR_REF);
 
   // Handle variable locations that don't actually depend on the instructions
   // in the program: constants and stack locations.
   if (DbgOperand.getKind() == SDDbgOperand::FRAMEIX ||
       DbgOperand.getKind() == SDDbgOperand::CONST)
     return EmitDbgValueFromSingleOp(SD, VRBaseMap);
 
+  // Immediately fold any indirectness from the LLVM-IR intrinsic into the
+  // expression:
+  if (SD->isIndirect()) {
+    std::vector<uint64_t> Elts = {dwarf::DW_OP_deref};
+    Expr = DIExpression::append(Expr, Elts);
+  }
+
   // It may not be immediately possible to identify the MachineInstr that
   // defines a VReg, it can depend for example on the order blocks are
   // emitted in. When this happens, or when further analysis is needed later,
   // produce an instruction like this:
   //
   //    DBG_INSTR_REF %0:gr64, 0, !123, !456
   //
   // i.e., point the instruction at the vreg, and patch it up later in

llvm/test/DebugInfo/X86/instr-ref-dbg-declare.ll

+; RUN: llc %s -stop-before=finalize-isel -o - \
+; RUN:     -experimental-debug-variable-locations=true \
+; RUN:  | FileCheck %s
+
+;; Copy of DebugInfo/COFF/types-array-advanced.ll. This features a dbg.declare 
+;; of something (dynamic alloca) that isn't an argument, causing a SDDbgValue
+;; with the indirect flag set to be emitted. Test that it's preserved in
+;; instruction referencing mode -- we don't have an IsIndirect flag on
+;; DBG_INSTR_REF, so it gets encoded as an additional DW_OP_deref.
+;;
+;; NB: the original test has an additional spurious DW_OP_deref in the
+;; dbg.declare's arguments, which is preserved here, translating to two derefs.
+
+; CHECK: DBG_INSTR_REF 1, 2, !{{[0-9]+}}, !DIExpression(DW_OP_deref, DW_OP_deref)
+
+source_filename = "test/DebugInfo/COFF/types-array-advanced.ll"
+target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
+target triple = "i686-pc-windows-msvc18.0.31101"
+
+%struct.incomplete_struct = type { i32 }
+
+@"\01?multi_dim_arr@@3PAY146DA" = global [2 x [5 x [7 x i8]]] zeroinitializer, align 1, !dbg !0
+@"\01?p_incomplete_struct_arr@@3PAY02Uincomplete_struct@@A" = global [3 x i8]* null, align 4, !dbg !6
+@"\01?incomplete_struct_arr@@3PAUincomplete_struct@@A" = global [3 x %struct.incomplete_struct] zeroinitializer, align 4, !dbg !16
+@"\01?typedef_arr@@3SDHD" = constant [4 x i32] zeroinitializer, align 4, !dbg !18
+
+; Function Attrs: nounwind
+define void @"\01?foo@@YAXH@Z"(i32 %x) #0 !dbg !35 {
+entry:
+  %x.addr = alloca i32, align 4
+  %saved_stack = alloca i8*, align 4
+  store i32 %x, i32* %x.addr, align 4
+  %0 = load i32, i32* %x.addr, align 4, !dbg !41
+  %1 = call i8* @llvm.stacksave(), !dbg !42
+  store i8* %1, i8** %saved_stack, align 4, !dbg !42
+  %vla = alloca i32, i32 %0, align 4, !dbg !42
+  ;; This dbg.declare turns into a DBG_INSTR_REF, rather than an argument
+  ;; DBG_VALUE. It needs to keep the extra indirectness.
+  call void @llvm.dbg.declare(metadata i32* %vla, metadata !43, metadata !47), !dbg !48
+  %arrayidx = getelementptr inbounds i32, i32* %vla, i32 0, !dbg !49
+  store i32 0, i32* %arrayidx, align 4, !dbg !50
+  %2 = load i8*, i8** %saved_stack, align 4, !dbg !51
+  call void @llvm.stackrestore(i8* %2), !dbg !51
+  ret void, !dbg !51
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+; Function Attrs: nounwind
+declare i8* @llvm.stacksave()
+
+; Function Attrs: nounwind
+declare void @llvm.stackrestore(i8*)
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!32, !33}
+!llvm.ident = !{!34}
+
+!0 = distinct !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = !DIGlobalVariable(name: "multi_dim_arr", linkageName: "\01?multi_dim_arr@@3PAY146DA", scope: !2, file: !3, line: 1, type: !26, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang version 3.9.0 (trunk 273874)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
+!3 = !DIFile(filename: "t.cpp", directory: "/")
+!4 = !{}
+!5 = !{!0, !6, !16, !18}
+!6 = distinct !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
+!7 = !DIGlobalVariable(name: "p_incomplete_struct_arr", linkageName: "\01?p_incomplete_struct_arr@@3PAY02Uincomplete_struct@@A", scope: !2, file: !3, line: 3, type: !8, isLocal: false, isDefinition: true)
+!8 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !9, size: 32, align: 32)
+!9 = !DICompositeType(tag: DW_TAG_array_type, baseType: !10, elements: !14)
+!10 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "incomplete_struct", file: !3, line: 4, size: 32, align: 32, elements: !11, identifier: ".?AUincomplete_struct@@")
+!11 = !{!12}
+!12 = !DIDerivedType(tag: DW_TAG_member, name: "s1", scope: !10, file: !3, line: 5, baseType: !13, size: 32, align: 32)
+!13 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!14 = !{!15}
+!15 = !DISubrange(count: 3)
+!16 = distinct !DIGlobalVariableExpression(var: !17, expr: !DIExpression())
+!17 = !DIGlobalVariable(name: "incomplete_struct_arr", linkageName: "\01?incomplete_struct_arr@@3PAUincomplete_struct@@A", scope: !2, file: !3, line: 6, type: !9, isLocal: false, isDefinition: true)
+!18 = distinct !DIGlobalVariableExpression(var: !19, expr: !DIExpression())
+!19 = !DIGlobalVariable(name: "typedef_arr", linkageName: "\01?typedef_arr@@3SDHD", scope: !2, file: !3, line: 14, type: !20, isLocal: false, isDefinition: true)
+!20 = !DICompositeType(tag: DW_TAG_array_type, baseType: !21, size: 128, align: 32, elements: !24)
+!21 = !DIDerivedType(tag: DW_TAG_typedef, name: "T_INT", file: !3, line: 13, baseType: !22)
+!22 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !23)
+!23 = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: !13)
+!24 = !{!25}
+!25 = !DISubrange(count: 4)
+!26 = !DICompositeType(tag: DW_TAG_array_type, baseType: !27, size: 560, align: 8, elements: !28)
+!27 = !DIBasicType(name: "char", size: 8, align: 8, encoding: DW_ATE_signed_char)
+!28 = !{!29, !30, !31}
+!29 = !DISubrange(count: 2)
+!30 = !DISubrange(count: 5)
+!31 = !DISubrange(count: 7)
+!32 = !{i32 2, !"CodeView", i32 1}
+!33 = !{i32 2, !"Debug Info Version", i32 3}
+!34 = !{!"clang version 3.9.0 (trunk 273874)"}
+!35 = distinct !DISubprogram(name: "foo", linkageName: "\01?foo@@YAXH@Z", scope: !3, file: !3, line: 8, type: !36, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: false, unit: !2, retainedNodes: !4)
+!36 = !DISubroutineType(types: !37)
+!37 = !{null, !13}
+!38 = !DILocalVariable(name: "x", arg: 1, scope: !35, file: !3, line: 8, type: !13)
+!39 = !DIExpression()
+!40 = !DILocation(line: 8, column: 14, scope: !35)
+!41 = !DILocation(line: 9, column: 21, scope: !35)
+!42 = !DILocation(line: 9, column: 4, scope: !35)
+!43 = !DILocalVariable(name: "dyn_size_arr", scope: !35, file: !3, line: 9, type: !44)
+!44 = !DICompositeType(tag: DW_TAG_array_type, baseType: !13, align: 32, elements: !45)
+!45 = !{!46}
+!46 = !DISubrange(count: -1)
+!47 = !DIExpression(DW_OP_deref)
+!48 = !DILocation(line: 9, column: 8, scope: !35)
+!49 = !DILocation(line: 10, column: 4, scope: !35)
+!50 = !DILocation(line: 10, column: 20, scope: !35)
+!51 = !DILocation(line: 11, column: 1, scope: !35)
+