[llvm] Add new DI Flag IsZeroSize for D101237 [[no_unique_address]]

[jankratochvil]

Summary

It is non-trivial as I have tried to reuse the ReservedBit4 so posting as a separate patch for D101237.

[dblaikie]

DICompositeType has a "SizeInBits" field - can that be used to specify a size of 0, instead of adding a new flag to convey this?

[aprantl]

In C and Swift we express zero-sized types by just setting their bitsize to 0. Why doesn't this work for OCaml?

[deadalnix]

llvm/include/llvm-c/DebugInfo.h

34

If you change the C API, please make sure you add a note about it. It would also be preferable to add a test case.

Other already have asked question about the approach here, so I won't double down there.

llvm/bindings/ocaml/debuginfo/debuginfo_ocaml.c

 // This is identical to the definition in llvm_debuginfo.ml:DIFlag.t
 typedef enum {
   i_DIFlagZero,
   i_DIFlagPrivate,
   i_DIFlagProtected,
   i_DIFlagPublic,
   i_DIFlagFwdDecl,
   i_DIFlagAppleBlock,
-  i_DIFlagReservedBit4,
+  i_DIFlagIsZeroSize,
   i_DIFlagVirtual,
   i_DIFlagArtificial,
   i_DIFlagExplicit,
   i_DIFlagPrototyped,
   i_DIFlagObjcClassComplete,
   i_DIFlagObjectPointer,
   i_DIFlagVector,
   i_DIFlagStaticMember,
static LLVMDIFlags map_DIFlag(LLVMDIFlag_i DIF) {
   case i_DIFlagProtected:
     return LLVMDIFlagProtected;
   case i_DIFlagPublic:
     return LLVMDIFlagPublic;
   case i_DIFlagFwdDecl:
     return LLVMDIFlagFwdDecl;
   case i_DIFlagAppleBlock:
     return LLVMDIFlagAppleBlock;
-  case i_DIFlagReservedBit4:
-    return LLVMDIFlagReservedBit4;
+  case i_DIFlagIsZeroSize:
+    return LLVMDIFlagIsZeroSize;
   case i_DIFlagVirtual:
     return LLVMDIFlagVirtual;
   case i_DIFlagArtificial:
     return LLVMDIFlagArtificial;
   case i_DIFlagExplicit:
     return LLVMDIFlagExplicit;
   case i_DIFlagPrototyped:
     return LLVMDIFlagPrototyped;

llvm/bindings/ocaml/debuginfo/llvm_debuginfo.ml

 module DIFlag = struct
   type t =
     | Zero
     | Private
     | Protected
     | Public
     | FwdDecl
     | AppleBlock
-    | ReservedBit4
+    | IsZeroSize
     | Virtual
     | Artificial
     | Explicit
     | Prototyped
     | ObjcClassComplete
     | ObjectPointer
     | Vector
     | StaticMember

llvm/bindings/ocaml/debuginfo/llvm_debuginfo.mli

 module DIFlag : sig
   type t =
     | Zero
     | Private
     | Protected
     | Public
     | FwdDecl
     | AppleBlock
-    | ReservedBit4
+    | IsZeroSize
     | Virtual
     | Artificial
     | Explicit
     | Prototyped
     | ObjcClassComplete
     | ObjectPointer
     | Vector
     | StaticMember

llvm/include/llvm-c/DebugInfo.h

  */
 typedef enum {
   LLVMDIFlagZero = 0,
   LLVMDIFlagPrivate = 1,
   LLVMDIFlagProtected = 2,
   LLVMDIFlagPublic = 3,
   LLVMDIFlagFwdDecl = 1 << 2,
   LLVMDIFlagAppleBlock = 1 << 3,
-  LLVMDIFlagReservedBit4 = 1 << 4,
+  LLVMDIFlagIsZeroSize = 1 << 4,
   LLVMDIFlagVirtual = 1 << 5,
   LLVMDIFlagArtificial = 1 << 6,
   LLVMDIFlagExplicit = 1 << 7,
   LLVMDIFlagPrototyped = 1 << 8,
   LLVMDIFlagObjcClassComplete = 1 << 9,
   LLVMDIFlagObjectPointer = 1 << 10,
   LLVMDIFlagVector = 1 << 11,
   LLVMDIFlagStaticMember = 1 << 12,
typedef enum {
   LLVMDIFlagEnumClass = 1 << 24,
   LLVMDIFlagFixedEnum = LLVMDIFlagEnumClass, // Deprecated.
   LLVMDIFlagThunk = 1 << 25,
   LLVMDIFlagNonTrivial = 1 << 26,
   LLVMDIFlagBigEndian = 1 << 27,
   LLVMDIFlagLittleEndian = 1 << 28,
   LLVMDIFlagAllCallsDescribed = 1 << 29,
   LLVMDIFlagIndirectVirtualBase = (1 << 2) | (1 << 5),
-  LLVMDIFlagAccessibility = LLVMDIFlagPrivate | LLVMDIFlagProtected |
-                            LLVMDIFlagPublic,
+  LLVMDIFlagAccessibility =
+      LLVMDIFlagPrivate | LLVMDIFlagProtected | LLVMDIFlagPublic,
   LLVMDIFlagPtrToMemberRep = LLVMDIFlagSingleInheritance |
                              LLVMDIFlagMultipleInheritance |
                              LLVMDIFlagVirtualInheritance
 } LLVMDIFlags;
 
 /**
  * Source languages known by DWARF.
  */

llvm/include/llvm/IR/DebugInfoFlags.def

 
 HANDLE_DI_FLAG(0, Zero) // Use it as zero value.
                         // For example: void foo(DIFlags Flags = FlagZero).
 HANDLE_DI_FLAG(1, Private)
 HANDLE_DI_FLAG(2, Protected)
 HANDLE_DI_FLAG(3, Public)
 HANDLE_DI_FLAG((1 << 2), FwdDecl)
 HANDLE_DI_FLAG((1 << 3), AppleBlock)
-// Used to be BlockByRef, can be reused for anything except DICompositeType.
-HANDLE_DI_FLAG((1 << 4), ReservedBit4)
+// IsZeroSize is valid only for DIDerivedType.
+// This bit was used as BlockByrefStruct for DICompositeType (D67453), do not
+// reuse it for DICompositeType so that Verifier can detect old bitcode.
+HANDLE_DI_FLAG((1 << 4), IsZeroSize)
 HANDLE_DI_FLAG((1 << 5), Virtual)
 HANDLE_DI_FLAG((1 << 6), Artificial)
 HANDLE_DI_FLAG((1 << 7), Explicit)
 HANDLE_DI_FLAG((1 << 8), Prototyped)
 HANDLE_DI_FLAG((1 << 9), ObjcClassComplete)
 HANDLE_DI_FLAG((1 << 10), ObjectPointer)
 HANDLE_DI_FLAG((1 << 11), Vector)
 HANDLE_DI_FLAG((1 << 12), StaticMember)

llvm/lib/IR/Verifier.cpp

AssertDI(isType(N.getRawBaseType()), "invalid base type", &N,
            N.getRawBaseType());
 
   AssertDI(!N.getRawElements() || isa<MDTuple>(N.getRawElements()),
            "invalid composite elements", &N, N.getRawElements());
   AssertDI(isType(N.getRawVTableHolder()), "invalid vtable holder", &N,
            N.getRawVTableHolder());
   AssertDI(!hasConflictingReferenceFlags(N.getFlags()),
            "invalid reference flags", &N);
-  unsigned DIBlockByRefStruct = 1 << 4;
+  const unsigned DIBlockByRefStruct = 1 << 4;
+  static_assert(DIBlockByRefStruct == DINode::FlagIsZeroSize,
+                "DI Flag BlockByRefStruct == IsZeroSize");
   AssertDI((N.getFlags() & DIBlockByRefStruct) == 0,
            "DIBlockByRefStruct on DICompositeType is no longer supported", &N);
 
   if (N.isVector()) {
     const DINodeArray Elements = N.getElements();
     AssertDI(Elements.size() == 1 &&
              Elements[0]->getTag() == dwarf::DW_TAG_subrange_type,
              "invalid vector, expected one element of type subrange", &N);

llvm/test/Verifier/blockbyref.ll

 }
 
 declare void @llvm.dbg.declare(metadata, metadata, metadata)
 
 !llvm.module.flags = !{!0}
 !0 = !{i32 2, !"Debug Info Version", i32 3}
 !1 = distinct !DISubprogram()
 !2 = !DILocalVariable(scope: !1, type: !3)
-!3 = !DICompositeType(tag: DW_TAG_structure_type, flags: DIFlagReservedBit4)
+!3 = !DICompositeType(tag: DW_TAG_structure_type, flags: DIFlagIsZeroSize)