[WIP] Allow entry values in complex expressions. NOT FOR COMMIT

llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp

if (HasComplexExpression && DwarfRegs.size() > 1) {
     LocationKind = Unknown;
     return false;
   }
 
   // Handle simple register locations. If we are supposed to emit
   // a call site parameter expression and if that expression is just a register
   // location, emit it with addBReg and offset 0, because we should emit a DWARF
   // expression representing a value, rather than a location.
-  if (!isMemoryLocation() && !HasComplexExpression && (!isParameterValue() ||
-                                                       isEntryValue())) {
+  if ((!isMemoryLocation() && !HasComplexExpression && !isParameterValue()) ||
+      isEntryValue()) {
     for (auto &Reg : DwarfRegs) {
       if (Reg.DwarfRegNo >= 0)
         addReg(Reg.DwarfRegNo, Reg.Comment);
       addOpPiece(Reg.Size);
     }
 
     if (isEntryValue())
       finalizeEntryValue();
 
-    if (isEntryValue() && !isParameterValue() && DwarfVersion >= 4)
-      emitOp(dwarf::DW_OP_stack_value);
+    if (isEntryValue() && !isParameterValue() && isRegisterLocation())
+      LocationKind = Implicit;
 
     DwarfRegs.clear();
     return true;
   }
 
   // Don't emit locations that cannot be expressed without DW_OP_stack_value.
   if (DwarfVersion < 4)
     if (any_of(ExprCursor, [](DIExpression::ExprOperand Op) -> bool {

llvm/lib/IR/DebugInfoMetadata.cpp

case dwarf::DW_OP_swap: {
       break;
     }
     case dwarf::DW_OP_LLVM_entry_value: {
       // An entry value operator must appear at the beginning and the number of
       // operations it cover can currently only be 1, because we support only
       // entry values of a simple register location. One reason for this is that
       // we currently can't calculate the size of the resulting DWARF block for
       // other expressions.
-      return I->get() == expr_op_begin()->get() && I->getArg(0) == 1 &&
-             getNumElements() == 2;
+      return I->get() == expr_op_begin()->get() && I->getArg(0) == 1;
     }
     case dwarf::DW_OP_LLVM_convert:
     case dwarf::DW_OP_LLVM_tag_offset:
     case dwarf::DW_OP_constu:
     case dwarf::DW_OP_plus_uconst:
     case dwarf::DW_OP_plus:
     case dwarf::DW_OP_minus:
     case dwarf::DW_OP_mul:

llvm/test/DebugInfo/MIR/X86/complex-entry-value.mir

+# RUN: llc -debug-entry-values -start-after=livedebugvalues -o - %s -filetype=obj | llvm-dwarfdump - | FileCheck %s
+
+# Based on the the following reproducer:
+#
+# extern void use_and_clobber(int);
+#
+# int callee(int p) {
+#   int local = p + 1;
+#   use_and_clobber(p);
+#   return 0;
+# }
+
+--- |
+  ; ModuleID = 'foo.c'
+  source_filename = "foo.c"
+  target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+  target triple = "x86_64-unknown-linux-gnu"
+
+  ; Function Attrs: nounwind uwtable
+  define dso_local i32 @callee(i32 %p) local_unnamed_addr #0 !dbg !12 {
+  entry:
+    call void @llvm.dbg.value(metadata i32 %p, metadata !16, metadata !DIExpression()), !dbg !18
+    call void @llvm.dbg.value(metadata i32 %p, metadata !17, metadata !DIExpression(DW_OP_plus_uconst, 1, DW_OP_stack_value)), !dbg !18
+    tail call void @use_and_clobber(i32 %p) #2, !dbg !19
+    ret i32 0, !dbg !20
+  }
+
+  declare !dbg !4 dso_local void @use_and_clobber(i32) local_unnamed_addr
+
+  ; Function Attrs: nounwind readnone speculatable willreturn
+  declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+  ; Function Attrs: nounwind
+  declare void @llvm.stackprotector(i8*, i8**) #2
+
+  attributes #0 = { nounwind uwtable }
+  attributes #1 = { nounwind readnone speculatable willreturn }
+  attributes #2 = { nounwind }
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!8, !9, !10}
+  !llvm.ident = !{!11}
+
+  !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
+  !1 = !DIFile(filename: "foo.c", directory: "/")
+  !2 = !{}
+  !3 = !{!4}
+  !4 = !DISubprogram(name: "use_and_clobber", scope: !1, file: !1, line: 1, type: !5, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+  !5 = !DISubroutineType(types: !6)
+  !6 = !{null, !7}
+  !7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !8 = !{i32 2, !"Dwarf Version", i32 4}
+  !9 = !{i32 2, !"Debug Info Version", i32 3}
+  !10 = !{i32 1, !"wchar_size", i32 4}
+  !11 = !{!"clang version 10.0.0"}
+  !12 = distinct !DISubprogram(name: "callee", scope: !1, file: !1, line: 3, type: !13, scopeLine: 3, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !15)
+  !13 = !DISubroutineType(types: !14)
+  !14 = !{!7, !7}
+  !15 = !{!16, !17}
+  !16 = !DILocalVariable(name: "p", arg: 1, scope: !12, file: !1, line: 3, type: !7, flags: DIFlagArgumentNotModified)
+  !17 = !DILocalVariable(name: "local", scope: !12, file: !1, line: 4, type: !7)
+  !18 = !DILocation(line: 0, scope: !12)
+  !19 = !DILocation(line: 5, scope: !12)
+  !20 = !DILocation(line: 6, scope: !12)
+
+...
+---
+name:            callee
+alignment:       16
+tracksRegLiveness: true
+liveins:
+  - { reg: '$edi' }
+frameInfo:
+  stackSize:       8
+  offsetAdjustment: -8
+  maxAlignment:    1
+  adjustsStack:    true
+  hasCalls:        true
+  maxCallFrameSize: 0
+callSites:
+  - { bb: 0, offset: 6, fwdArgRegs:
+      - { arg: 0, reg: '$edi' } }
+machineFunctionInfo: {}
+body:             |
+  bb.0.entry:
+    liveins: $edi
+
+    DBG_VALUE $edi, $noreg, !16, !DIExpression(), debug-location !18
+    DBG_VALUE $edi, $noreg, !16, !DIExpression(), debug-location !18
+    DBG_VALUE $edi, $noreg, !16, !DIExpression(), debug-location !18
+    frame-setup PUSH64r undef $rax, implicit-def $rsp, implicit $rsp
+    CFI_INSTRUCTION def_cfa_offset 16
+    DBG_VALUE $edi, $noreg, !17, !DIExpression(DW_OP_plus_uconst, 1, DW_OP_stack_value), debug-location !18
+    CALL64pcrel32 @use_and_clobber, csr_64, implicit $rsp, implicit $ssp, implicit $edi, implicit-def $rsp, implicit-def $ssp, debug-location !19
+    DBG_VALUE $edi, $noreg, !16, !DIExpression(DW_OP_LLVM_entry_value, 1), debug-location !18
+    DBG_VALUE $edi, $noreg, !17, !DIExpression(DW_OP_LLVM_entry_value, 1, DW_OP_plus_uconst, 1, DW_OP_stack_value), debug-location !18
+    $eax = XOR32rr undef $eax, undef $eax, implicit-def dead $eflags, debug-location !20
+    $rcx = frame-destroy POP64r implicit-def $rsp, implicit $rsp, debug-location !20
+    CFI_INSTRUCTION def_cfa_offset 8, debug-location !20
+    RETQ killed $eax, debug-location !20
+
+...
+
+# Verify that we emit a correct location list entry when local is described by an entry value.
+# The DBG_VALUE using the entry value has been manually added to this test.
+
+# CHECK: [0x0000000000000001,  0x0000000000000006): DW_OP_breg5 RDI+1, DW_OP_constu 0xffffffff, DW_OP_and, DW_OP_stack_value
+# CHECK: [0x0000000000000006,  0x000000000000000a): DW_OP_GNU_entry_value(DW_OP_reg5 RDI), DW_OP_constu 0xffffffff, DW_OP_and, DW_OP_plus_uconst 0x1, DW_OP_stack_value)