attributes: introduce allockind attr for describing allocator fn behavior

[durin42]

Summary

I chose to encode the allockind information in a string constant because
otherwise we would get a bit of an explosion of keywords to deal with
the possible permutations of allocation function types.

I'm not sure that CodeGen.h is the correct place for this enum, but it
seemed to kind of match the UWTableKind enum so I put it in the same
place. Constructive suggestions on a better location most certainly
encouraged.

[aykevl]

Not a real review but I found this which looks like a bug.

llvm/lib/AsmParser/LLParser.cpp

2061–2062

This looks incorrect to me.

[durin42]

llvm/lib/AsmParser/LLParser.cpp

2061–2062

Good catch, thanks!

[nikic]

llvm/docs/LangRef.rst

1576 ↗

(On Diff #425839)

I think I'd prefer using alloc rather than new terminology here. new is a C++ism.

1578 ↗

(On Diff #425839)

I think this needs to be a bit more precise. This function a) return a new block of memory or null, b) if the result is non-null, the memory contents from the start of the new block up to the minimum of the original allocation size and new allocation size match that of the allocptr argument and c) the allocptr argument is invalidated (in the sense of losing provenance) even if the function returns the same address.

1580 ↗

(On Diff #425839)

Can this be used only in conjunction with new or also with resize (where, in the latter case, it would refer only to memory past the original allocation size).

1583 ↗

(On Diff #425839)

Can only be used in conjunction with new and resize, presumably?

llvm/include/llvm/AsmParser/LLParser.h

23

Unnecessary include.

llvm/include/llvm/Support/CodeGen.h

111

I don't think CodeGen.h is a good fit for this, this doesn't really have anything to do with codegen. Maybe placing it directly in Attributes.h is fine (we can't have it in MemoryBuiltins.h due to layering).

llvm/lib/AsmParser/LLParser.cpp

2072

Include A in message? I'd also expect a test case for at least this error condition.

llvm/lib/IR/Attributes.cpp

458

SmallVector

[durin42]

I also renamed the enum entry from New to Alloc, hopefully that's what you had in mind.

[nikic]

llvm/docs/LangRef.rst

1581 ↗

(On Diff #426407)

"string is" -> "string contains"?

1584 ↗

(On Diff #426407)

Should reference "alloc" now. Also, I'd suggest to rename resize -> realloc to fully stick with the usual alloc/realloc/free terminology.

1601 ↗

(On Diff #426407)

Would it be preferable to forbid them (in the IR verifier) instead?

llvm/include/llvm/Support/CodeGen.h

19

Changes no longer needed.

llvm/lib/IR/Attributes.cpp

461

Can drop the braces from these, as they're single-line.

llvm/test/Assembler/allockind-missing.ll

4 ↗

(On Diff #426407)

Oh, fancy. TIL about #@LINE-1.

[durin42]

llvm/docs/LangRef.rst

1601 ↗

(On Diff #426407)

I guess. I've talked myself out of that a few times, because I could envision an allocator where free() needs the alignment passed in for some reason and then it might be nice to mark it as allocalign? I dunno.

I've added the validation now, and tweaked the langref. I guess we can always relax it...

[nikic]

llvm/docs/LangRef.rst

1592 ↗

(On Diff #426774)

"new" -> "alloc" here

llvm/include/llvm/IR/Attributes.h

49

Space before comment is off here.

llvm/lib/IR/Attributes.cpp

458

Can use StringRef here, as strings are constant?

llvm/lib/IR/Verifier.cpp

2091 ↗

(On Diff #426774)

This enumeration of different combinations seems a bit awkward, maybe we can do something along these lines instead?

AllocFnKind Type = K & (AllocFnKind::Alloc | AllocFnKind::Realloc | AllocFnKind::Free);
if (!is_contained(Type, {AllocFnKind::Alloc, AllocFnKind::Realloc, AllocFnKind::Free))
  CheckFailed(...);

2094 ↗

(On Diff #426774)

The != AllocFnKind::Unknown checks here aren't really necessary, and imho don't really add to readability either. (K & AllocFnKind::Free) should be directly usable as a boolean. (Though I don't care strongly about this.)

[aykevl]

llvm/docs/LangRef.rst

1584 ↗

(On Diff #426774)

Is it worth saying something about alloc(0)? C malloc(0) may or may not return NULL depending on the implementation:

If the size of the space requested is zero, the behavior is implementation-defined: either a null pointer is returned to indicate an error, or the behavior is as if the size were some nonzero value, except that the returned pointer shall not be used to access an object.

[nikic]

llvm/docs/LangRef.rst

1584 ↗

(On Diff #426774)

I guess we may want to omit the "if the allocation fails" here (and just make null a valid value -- unless the return is nonnull of course), but I don't think a more specific guarantee on the behavior of zero-sized allocations is needed for the kinds of optimizations we're interested in performing. Or do you have something in mind where this would matter?

For reference, the wording for allocsize is:

This attribute indicates that the annotated function will always return at least a given number of bytes (or null)

It does not further specify in which cases null/non-null may be returned.

[durin42]

llvm/lib/IR/Verifier.cpp

2091 ↗

(On Diff #426774)

Very nice, I like it. Thanks!

2094 ↗

(On Diff #426774)

It's not: error: could not convert ‘llvm::BitmaskEnumDetail::operator&<llvm::AllocFnKind>(Kind, llvm::AllocFnKind::Free)’ from ‘llvm::AllocFnKind’ to ‘bool’

I think the BitmaskEnum stuff is getting in the way, and it's beyond my C++-fu to figure out how to allow them to be convertible to bool.

[nikic]

LGTM

llvm/docs/LangRef.rst

1589 ↗

(On Diff #427088)

Missing period at end of sentence.

llvm/include/llvm/Analysis/MemoryBuiltins.h

110

You don't define this function -- or at least not in this patch.

llvm/lib/IR/Verifier.cpp

2094 ↗

(On Diff #426774)

Oh yeah, BitmaskEnum is doing some serious magic here...

[durin42]

llvm/include/llvm/Analysis/MemoryBuiltins.h

110

Oh good catch, this prototype was in the wrong patch. I've moved it to the correct one. Thanks!

llvm/include/llvm/Analysis/MemoryBuiltins.h

 bool isAllocRemovable(const CallBase *V, const TargetLibraryInfo *TLI);
 
 /// Gets the alignment argument for an aligned_alloc-like function, using either
 /// built-in knowledge based on fuction names/signatures or allocalign
 /// attributes. Note: the Value returned may not indicate a valid alignment, per
 /// the definition of the allocalign attribute.
 Value *getAllocAlignment(const CallBase *V, const TargetLibraryInfo *TLI);
 
+/// Gets the AllocKind information for a function.
+AllocFnKind getAllocKind(const CallBase *CB, const TargetLibraryInfo *TLI);
+
 /// Return the size of the requested allocation.  With a trivial mapper, this is
 /// identical to calling getObjectSize(..., Exact).  A mapper function can be
 /// used to replace one Value* (operand to the allocation) with another.  This
 /// is useful when doing abstract interpretation.
 Optional<APInt> getAllocSize(const CallBase *CB,
                              const TargetLibraryInfo *TLI,
                              std::function<const Value*(const Value*)> Mapper);
 

llvm/include/llvm/AsmParser/LLParser.h

 
 #include "LLLexer.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/AsmParser/Parser.h"
 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/FMF.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/ModuleSummaryIndex.h"
+#include <cstdint>
 #include <map>
 
 namespace llvm {
   class Module;
   class ConstantRange;
   class FunctionType;
   class GlobalObject;
   class SMDiagnostic;
private:
     void parseOptionalDSOLocal(bool &DSOLocal);
     void parseOptionalVisibility(unsigned &Res);
     void parseOptionalDLLStorageClass(unsigned &Res);
     bool parseOptionalCallingConv(unsigned &CC);
     bool parseOptionalAlignment(MaybeAlign &Alignment,
                                 bool AllowParens = false);
     bool parseOptionalDerefAttrBytes(lltok::Kind AttrKind, uint64_t &Bytes);
     bool parseOptionalUWTableKind(UWTableKind &Kind);
+    bool parseAllocKind(AllocFnKind &Kind);
     bool parseScopeAndOrdering(bool IsAtomic, SyncScope::ID &SSID,
                                AtomicOrdering &Ordering);
     bool parseScope(SyncScope::ID &SSID);
     bool parseOrdering(AtomicOrdering &Ordering);
     bool parseOptionalStackAlignment(unsigned &Alignment);
     bool parseOptionalCommaAlign(MaybeAlign &Alignment, bool &AteExtraComma);
     bool parseOptionalCommaAddrSpace(unsigned &AddrSpace, LocTy &Loc,
                                      bool &AteExtraComma);

llvm/include/llvm/AsmParser/LLToken.h

enum Kind {
   kw_amdgpu_cs,
   kw_amdgpu_kernel,
   kw_amdgpu_gfx,
   kw_tailcc,
 
   // Attributes:
   kw_attributes,
   kw_allocalign,
+  kw_allockind,
   kw_allocsize,
   kw_alwaysinline,
   kw_argmemonly,
   kw_sanitize_address,
   kw_sanitize_hwaddress,
   kw_sanitize_memtag,
   kw_builtin,
   kw_byval,

llvm/include/llvm/Bitcode/LLVMBitCodes.h

enum AttributeKindCodes {
   ATTR_KIND_VSCALE_RANGE = 74,
   ATTR_KIND_SWIFT_ASYNC = 75,
   ATTR_KIND_NO_SANITIZE_COVERAGE = 76,
   ATTR_KIND_ELEMENTTYPE = 77,
   ATTR_KIND_DISABLE_SANITIZER_INSTRUMENTATION = 78,
   ATTR_KIND_NO_SANITIZE_BOUNDS = 79,
   ATTR_KIND_ALLOC_ALIGN = 80,
   ATTR_KIND_ALLOCATED_POINTER = 81,
+  ATTR_KIND_ALLOC_KIND = 82,
 };
 
 enum ComdatSelectionKindCodes {
   COMDAT_SELECTION_KIND_ANY = 1,
   COMDAT_SELECTION_KIND_EXACT_MATCH = 2,
   COMDAT_SELECTION_KIND_LARGEST = 3,
   COMDAT_SELECTION_KIND_NO_DUPLICATES = 4,
   COMDAT_SELECTION_KIND_SAME_SIZE = 5,

llvm/include/llvm/IR/Attributes.h

 class FoldingSetNodeID;
 class Function;
 class LLVMContext;
 class Type;
 
 //===----------------------------------------------------------------------===//
 /// \class
 /// Functions, function parameters, and return types can have attributes
 /// to indicate how they should be treated by optimizations and code
 /// generation. This class represents one of those attributes. It's light-weight
 /// and should be passed around by-value.
 class Attribute {
 public:
   /// This enumeration lists the attributes that can be associated with
   /// parameters, function results, or the function itself.
   ///
   /// Note: The `uwtable' attribute is about the ABI or the user mandating an
public:
 
   /// Returns the maximum value for the vscale_range attribute or None when
   /// unknown.
   Optional<unsigned> getVScaleRangeMax() const;
 
   // Returns the unwind table kind.
   UWTableKind getUWTableKind() const;
 
+  // Returns the allocator function kind.
+  AllocFnKind getAllocKind() const;
+
   /// The Attribute is converted to a string of equivalent mnemonic. This
   /// is, presumably, for writing out the mnemonics for the assembly writer.
   std::string getAsString(bool InAttrGrp = false) const;
 
   /// Return true if this attribute belongs to the LLVMContext.
   bool hasParentContext(LLVMContext &C) const;
 
   /// Equality and non-equality operators.
public:
   Type *getByRefType() const;
   Type *getPreallocatedType() const;
   Type *getInAllocaType() const;
   Type *getElementType() const;
   std::pair<unsigned, Optional<unsigned>> getAllocSizeArgs() const;
   unsigned getVScaleRangeMin() const;
   Optional<unsigned> getVScaleRangeMax() const;
   UWTableKind getUWTableKind() const;
+  AllocFnKind getAllocKind() const;
   std::string getAsString(bool InAttrGrp = false) const;
 
   /// Return true if this attribute set belongs to the LLVMContext.
   bool hasParentContext(LLVMContext &C) const;
 
   using iterator = const Attribute *;
 
   iterator begin() const;
public:
 
   /// Get the number of dereferenceable_or_null bytes (or zero if unknown) of an
   /// arg.
   uint64_t getParamDereferenceableOrNullBytes(unsigned ArgNo) const;
 
   /// Get the unwind table kind requested for the function.
   UWTableKind getUWTableKind() const;
 
+  AllocFnKind getAllocKind() const;
+
   /// Return the attributes at the index as a string.
   std::string getAsString(unsigned Index, bool InAttrGrp = false) const;
 
   /// Return true if this attribute list belongs to the LLVMContext.
   bool hasParentContext(LLVMContext &C) const;
 
   //===--------------------------------------------------------------------===//
   // AttributeList Introspection
public:
   /// Add a vscale_range attribute, using the representation returned by
   /// Attribute.getIntValue().
   AttrBuilder &addVScaleRangeAttrFromRawRepr(uint64_t RawVScaleRangeRepr);
 
   /// This turns the unwind table kind into the form used internally in
   /// Attribute.
   AttrBuilder &addUWTableAttr(UWTableKind Kind);
 
+  // This turns the allocator kind into the form used internally in Attribute.
+  AttrBuilder &addAllocKindAttr(AllocFnKind Kind);
+
   ArrayRef<Attribute> attrs() const { return Attrs; }
 
   bool operator==(const AttrBuilder &B) const;
   bool operator!=(const AttrBuilder &B) const { return !(*this == B); }
 };
 
 namespace AttributeFuncs {
 

llvm/include/llvm/IR/Attributes.td

 /// Alignment of parameter (5 bits) stored as log2 of alignment with +1 bias.
 /// 0 means unaligned (different from align(1)).
 def Alignment : IntAttr<"align", [ParamAttr, RetAttr]>;
 
 /// Parameter of a function that tells us the alignment of an allocation, as in
 /// aligned_alloc and aligned ::operator::new.
 def AllocAlign: EnumAttr<"allocalign", [ParamAttr]>;
 
+/// Describes behavior of an allocator function in terms of known properties.
+def AllocKind: IntAttr<"allockind", [FnAttr]>;
+
 /// Parameter is the pointer to be maniuplated by the allocator function.
 def AllocatedPointer : EnumAttr<"allocptr", [ParamAttr]>;
 
 /// The result of the function is guaranteed to point to a number of bytes that
 /// we can determine if we know the value of the function's arguments.
 def AllocSize : IntAttr<"allocsize", [FnAttr]>;
 
 /// inline=always.

llvm/include/llvm/Support/CodeGen.h

 //===-- llvm/Support/CodeGen.h - CodeGen Concepts ---------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file define some types which define code generation concepts. For
 // example, relocation model.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_CODEGEN_H
 #define LLVM_SUPPORT_CODEGEN_H
 
+#include <cstdint>
+
+#include "llvm/ADT/BitmaskEnum.h"
+
 namespace llvm {
 
   // Relocation model types.
   namespace Reloc {
     // Cannot be named PIC due to collision with -DPIC
     enum Model { Static, PIC_, DynamicNoPIC, ROPI, RWPI, ROPI_RWPI };
   }
 
namespace llvm {
   } // namespace ZeroCallUsedRegs
 
   enum class UWTableKind {
     None = 0,  ///< No unwind table requested
     Sync = 1,  ///< "Synchronous" unwind tables
     Async = 2, ///< "Asynchronous" unwind tables (instr precise)
     Default = 2,
   };
+
+  enum class AllocFnKind : uint64_t {
+    Unknown = 0,
+    New = 1 << 0,    // Allocator function returns a new allocation
+    Resize = 1 << 1, // Allocator function resizes the `allocptr` argument
+    Free = 1 << 2,   // Allocator function frees the `allocptr` argument
+    Uninitialized = 1 << 3, // Allocator function returns uninitialized memory
+    Zeroed = 1 << 4,        // Allocator function returns zeroed memory
+    Aligned = 1 << 5,       // Allocator function aligns allocations per the
+                            // `allocalign` argument
+    LLVM_MARK_AS_BITMASK_ENUM(/* LargestValue = */ Aligned)
+  };
+
   } // namespace llvm
 
 #endif

llvm/lib/AsmParser/LLLexer.cpp

#define KEYWORD(STR)                                                           \
 
   KEYWORD(cc);
   KEYWORD(c);
 
   KEYWORD(attributes);
 
   KEYWORD(alwaysinline);
   KEYWORD(allocalign);
+  KEYWORD(allockind);
   KEYWORD(allocsize);
   KEYWORD(argmemonly);
   KEYWORD(builtin);
   KEYWORD(byval);
   KEYWORD(inalloca);
   KEYWORD(cold);
   KEYWORD(convergent);
   KEYWORD(dereferenceable);

llvm/lib/AsmParser/LLParser.cpp

bool LLParser::parseEnumAttribute(Attribute::AttrKind Attr, AttrBuilder &B,
   }
   case Attribute::UWTable: {
     UWTableKind Kind;
     if (parseOptionalUWTableKind(Kind))
       return true;
     B.addUWTableAttr(Kind);
     return false;
   }
+  case Attribute::AllocKind: {
+    AllocFnKind Kind = AllocFnKind::Unknown;
+    if (parseAllocKind(Kind))
+      return true;
+    B.addAllocKindAttr(Kind);
+    return false;
+  }
   default:
     B.addAttribute(Attr);
     Lex.Lex();
     return false;
   }
 }
 
 /// parseFnAttributeValuePairs
bool LLParser::parseOptionalUWTableKind(UWTableKind &Kind) {
   else if (Lex.getKind() == lltok::kw_async)
     Kind = UWTableKind::Async;
   else
     return error(KindLoc, "expected unwind table kind");
   Lex.Lex();
   return parseToken(lltok::rparen, "expected ')'");
 }
 
+bool LLParser::parseAllocKind(AllocFnKind &Kind) {
+  Lex.Lex();
+  LocTy ParenLoc = Lex.getLoc();
+  if (!EatIfPresent(lltok::lparen))
+    return error(ParenLoc, "expected '('");
+  LocTy KindLoc = Lex.getLoc();
+  std::string Arg;
+  if (parseStringConstant(Arg))
+    return error(KindLoc, "expected allockind value");
+  for (StringRef A : llvm::split(Arg, ",")) {
+    if (A == "new") {
+      Kind |= AllocFnKind::New;
+    } else if (A == "resize") {
+      Kind |= AllocFnKind::Free;
+    } else if (A == "free") {
+      Kind |= AllocFnKind::Free;
+    } else if (A == "uninitialized") {
+      Kind |= AllocFnKind::Uninitialized;
+    } else if (A == "zeroed") {
+      Kind |= AllocFnKind::Zeroed;
+    } else if (A == "aligned") {
+      Kind |= AllocFnKind::Aligned;
+    } else {
+      return error(KindLoc, "unknown allockind");
+    }
+  }
+  ParenLoc = Lex.getLoc();
+  if (!EatIfPresent(lltok::rparen))
+    return error(ParenLoc, "expected ')'");
+  if (Kind == AllocFnKind::Unknown)
+    return error(KindLoc, "expected allockind value");
+  return false;
+}
+
 /// parseOptionalCommaAlign
 ///   ::=
 ///   ::= ',' align 4
 ///
 /// This returns with AteExtraComma set to true if it ate an excess comma at the
 /// end.
 bool LLParser::parseOptionalCommaAlign(MaybeAlign &Alignment,
                                        bool &AteExtraComma) {

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

static Attribute::AttrKind getAttrFromCode(uint64_t Code) {
   case bitc::ATTR_KIND_NON_NULL:
     return Attribute::NonNull;
   case bitc::ATTR_KIND_DEREFERENCEABLE:
     return Attribute::Dereferenceable;
   case bitc::ATTR_KIND_DEREFERENCEABLE_OR_NULL:
     return Attribute::DereferenceableOrNull;
   case bitc::ATTR_KIND_ALLOC_ALIGN:
     return Attribute::AllocAlign;
+  case bitc::ATTR_KIND_ALLOC_KIND:
+    return Attribute::AllocKind;
   case bitc::ATTR_KIND_ALLOC_SIZE:
     return Attribute::AllocSize;
   case bitc::ATTR_KIND_ALLOCATED_POINTER:
     return Attribute::AllocatedPointer;
   case bitc::ATTR_KIND_NO_RED_ZONE:
     return Attribute::NoRedZone;
   case bitc::ATTR_KIND_NO_RETURN:
     return Attribute::NoReturn;
case bitc::PARAMATTR_GRP_CODE_ENTRY: { // ENTRY: [grpid, idx, a0, a1, ...]
           else if (Kind == Attribute::DereferenceableOrNull)
             B.addDereferenceableOrNullAttr(Record[++i]);
           else if (Kind == Attribute::AllocSize)
             B.addAllocSizeAttrFromRawRepr(Record[++i]);
           else if (Kind == Attribute::VScaleRange)
             B.addVScaleRangeAttrFromRawRepr(Record[++i]);
           else if (Kind == Attribute::UWTable)
             B.addUWTableAttr(UWTableKind(Record[++i]));
+          else if (Kind == Attribute::AllocKind)
+            B.addAllocKindAttr(static_cast<AllocFnKind>(Record[++i]));
         } else if (Record[i] == 3 || Record[i] == 4) { // String attribute
           bool HasValue = (Record[i++] == 4);
           SmallString<64> KindStr;
           SmallString<64> ValStr;
 
           while (Record[i] != 0 && i != e)
             KindStr += Record[i++];
           assert(Record[i] == 0 && "Kind string not null terminated");

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
   case Attribute::InReg:
     return bitc::ATTR_KIND_IN_REG;
   case Attribute::JumpTable:
     return bitc::ATTR_KIND_JUMP_TABLE;
   case Attribute::MinSize:
     return bitc::ATTR_KIND_MIN_SIZE;
   case Attribute::AllocatedPointer:
     return bitc::ATTR_KIND_ALLOCATED_POINTER;
+  case Attribute::AllocKind:
+    return bitc::ATTR_KIND_ALLOC_KIND;
   case Attribute::Naked:
     return bitc::ATTR_KIND_NAKED;
   case Attribute::Nest:
     return bitc::ATTR_KIND_NEST;
   case Attribute::NoAlias:
     return bitc::ATTR_KIND_NO_ALIAS;
   case Attribute::NoBuiltin:
     return bitc::ATTR_KIND_NO_BUILTIN;

llvm/lib/IR/AttributeImpl.h

public:
   MaybeAlign getAlignment() const;
   MaybeAlign getStackAlignment() const;
   uint64_t getDereferenceableBytes() const;
   uint64_t getDereferenceableOrNullBytes() const;
   std::pair<unsigned, Optional<unsigned>> getAllocSizeArgs() const;
   unsigned getVScaleRangeMin() const;
   Optional<unsigned> getVScaleRangeMax() const;
   UWTableKind getUWTableKind() const;
+  AllocFnKind getAllocKind() const;
   std::string getAsString(bool InAttrGrp) const;
   Type *getAttributeType(Attribute::AttrKind Kind) const;
 
   using iterator = const Attribute *;
 
   iterator begin() const { return getTrailingObjects<Attribute>(); }
   iterator end() const { return begin() + NumAttrs; }
 

llvm/lib/IR/Attributes.cpp

 }
 
 UWTableKind Attribute::getUWTableKind() const {
   assert(hasAttribute(Attribute::UWTable) &&
          "Trying to get unwind table kind from non-uwtable attribute");
   return UWTableKind(pImpl->getValueAsInt());
 }
 
+AllocFnKind Attribute::getAllocKind() const {
+  assert(hasAttribute(Attribute::AllocKind) &&
+         "Trying to get allockind value from non-allockind attribute");
+  return AllocFnKind(pImpl->getValueAsInt());
+}
+
 std::string Attribute::getAsString(bool InAttrGrp) const {
   if (!pImpl) return {};
 
   if (isEnumAttribute())
     return getNameFromAttrKind(getKindAsEnum()).str();
 
   if (isTypeAttribute()) {
     std::string Result = getNameFromAttrKind(getKindAsEnum()).str();
if (Kind != UWTableKind::None) {
       return Kind == UWTableKind::Default
                  ? "uwtable"
                  : ("uwtable(" +
                     Twine(Kind == UWTableKind::Sync ? "sync" : "async") + ")")
                        .str();
     }
   }
 
+  if (hasAttribute(Attribute::AllocKind)) {
+    AllocFnKind Kind = getAllocKind();
+    std::vector<std::string> parts;
+    if ((Kind & AllocFnKind::New) != AllocFnKind::Unknown) {
+      parts.push_back("new");
+    }
+    if ((Kind & AllocFnKind::Resize) != AllocFnKind::Unknown) {
+      parts.push_back("resize");
+    }
+    if ((Kind & AllocFnKind::Free) != AllocFnKind::Unknown) {
+      parts.push_back("free");
+    }
+    if ((Kind & AllocFnKind::Uninitialized) != AllocFnKind::Unknown) {
+      parts.push_back("uninitialized");
+    }
+    if ((Kind & AllocFnKind::Zeroed) != AllocFnKind::Unknown) {
+      parts.push_back("zeroed");
+    }
+    if ((Kind & AllocFnKind::Aligned) != AllocFnKind::Unknown) {
+      parts.push_back("aligned");
+    }
+    return ("allockind(\"" +
+            Twine(llvm::join(parts.begin(), parts.end(), ",")) + "\")")
+        .str();
+  }
+
   // Convert target-dependent attributes to strings of the form:
   //
   //   "kind"
   //   "kind" = "value"
   //
   if (isStringAttribute()) {
     std::string Result;
     {

 Optional<unsigned> AttributeSet::getVScaleRangeMax() const {
   return SetNode ? SetNode->getVScaleRangeMax() : None;
 }
 
 UWTableKind AttributeSet::getUWTableKind() const {
   return SetNode ? SetNode->getUWTableKind() : UWTableKind::None;
 }
 
+AllocFnKind AttributeSet::getAllocKind() const {
+  return SetNode ? SetNode->getAllocKind() : AllocFnKind::Unknown;
+}
+
 std::string AttributeSet::getAsString(bool InAttrGrp) const {
   return SetNode ? SetNode->getAsString(InAttrGrp) : "";
 }
 
 bool AttributeSet::hasParentContext(LLVMContext &C) const {
   assert(hasAttributes() && "empty AttributeSet doesn't refer to any context");
   FoldingSetNodeID ID;
   SetNode->Profile(ID);

 }
 
 UWTableKind AttributeSetNode::getUWTableKind() const {
   if (auto A = findEnumAttribute(Attribute::UWTable))
     return A->getUWTableKind();
   return UWTableKind::None;
 }
 
+AllocFnKind AttributeSetNode::getAllocKind() const {
+  if (auto A = findEnumAttribute(Attribute::AllocKind))
+    return A->getAllocKind();
+  return AllocFnKind::Unknown;
+}
+
 std::string AttributeSetNode::getAsString(bool InAttrGrp) const {
   std::string Str;
   for (iterator I = begin(), E = end(); I != E; ++I) {
     if (I != begin())
       Str += ' ';
     Str += I->getAsString(InAttrGrp);
   }
   return Str;

 AttributeList::getParamDereferenceableOrNullBytes(unsigned Index) const {
   return getParamAttrs(Index).getDereferenceableOrNullBytes();
 }
 
 UWTableKind AttributeList::getUWTableKind() const {
   return getFnAttrs().getUWTableKind();
 }
 
+AllocFnKind AttributeList::getAllocKind() const {
+  return getFnAttrs().getAllocKind();
+}
+
 std::string AttributeList::getAsString(unsigned Index, bool InAttrGrp) const {
   return getAttributes(Index).getAsString(InAttrGrp);
 }
 
 AttributeSet AttributeList::getAttributes(unsigned Index) const {
   Index = attrIdxToArrayIdx(Index);
   if (!pImpl || Index >= getNumAttrSets())
     return {};

 }
 
 AttrBuilder &AttrBuilder::addUWTableAttr(UWTableKind Kind) {
   if (Kind == UWTableKind::None)
     return *this;
   return addRawIntAttr(Attribute::UWTable, uint64_t(Kind));
 }
 
+AttrBuilder &AttrBuilder::addAllocKindAttr(AllocFnKind Kind) {
+  return addRawIntAttr(Attribute::AllocKind, static_cast<uint64_t>(Kind));
+}
+
 Type *AttrBuilder::getTypeAttr(Attribute::AttrKind Kind) const {
   assert(Attribute::isTypeAttrKind(Kind) && "Not a type attribute");
   Attribute A = getAttribute(Kind);
   return A.isValid() ? A.getValueAsType() : nullptr;
 }
 
 AttrBuilder &AttrBuilder::addTypeAttr(Attribute::AttrKind Kind, Type *Ty) {
   return addAttribute(Attribute::get(Ctx, Kind, Ty));

llvm/lib/Transforms/Utils/CodeExtractor.cpp

if (Attr.isStringAttribute()) {
       case Attribute::NoSync:
       case Attribute::ReadNone:
       case Attribute::ReadOnly:
       case Attribute::ReturnsTwice:
       case Attribute::Speculatable:
       case Attribute::StackAlignment:
       case Attribute::WillReturn:
       case Attribute::WriteOnly:
+      case Attribute::AllocKind:
         continue;
       // Those attributes should be safe to propagate to the extracted function.
       case Attribute::AlwaysInline:
       case Attribute::Cold:
       case Attribute::DisableSanitizerInstrumentation:
       case Attribute::Hot:
       case Attribute::NoRecurse:
       case Attribute::InlineHint:

llvm/test/Bitcode/compatibility.ll

exit:
   ; CHECK: phi i32 [ %v1, %L1 ], [ %v2, %L2 ], [ %op1, %entry ]
 
   select i1 true, i32 0, i32 1
   ; CHECK: select i1 true, i32 0, i32 1
   select <2 x i1> <i1 true, i1 false>, <2 x i8> <i8 2, i8 3>, <2 x i8> <i8 3, i8 2>
   ; CHECK: select <2 x i1> <i1 true, i1 false>, <2 x i8> <i8 2, i8 3>, <2 x i8> <i8 3, i8 2>
 
   call void @f.nobuiltin() builtin
-  ; CHECK: call void @f.nobuiltin() #49
+  ; CHECK: call void @f.nobuiltin() #50
 
   call fastcc noalias i32* @f.noalias() noinline
   ; CHECK: call fastcc noalias i32* @f.noalias() #12
   tail call ghccc nonnull i32* @f.nonnull() minsize
   ; CHECK: tail call ghccc nonnull i32* @f.nonnull() #7
 
   freeze i32 %op1
   ; CHECK: freeze i32 %op1

 ; CHECK: Function Attrs: allocsize(0)
 ; CHECK: declare void @f.allocsize_one(i32)
 ; CHECK: Function Attrs: allocsize(1,0)
 ; CHECK: declare void @f.allocsize_two(i32, i32)
 
 declare void @f.nosanitize_bounds() nosanitize_bounds
 ; CHECK: declare void @f.nosanitize_bounds() #48
 
+declare void @f.allockind() allockind("new,uninitialized")
+; CHECK: declare void @f.allockind() #49
+
 ; CHECK: attributes #0 = { alignstack=4 }
 ; CHECK: attributes #1 = { alignstack=8 }
 ; CHECK: attributes #2 = { alwaysinline }
 ; CHECK: attributes #3 = { cold }
 ; CHECK: attributes #4 = { convergent }
 ; CHECK: attributes #5 = { inlinehint }
 ; CHECK: attributes #6 = { jumptable }
 ; CHECK: attributes #7 = { minsize }

 ; CHECK: attributes #41 = { writeonly }
 ; CHECK: attributes #42 = { speculatable }
 ; CHECK: attributes #43 = { strictfp }
 ; CHECK: attributes #44 = { nosanitize_coverage }
 ; CHECK: attributes #45 = { disable_sanitizer_instrumentation }
 ; CHECK: attributes #46 = { allocsize(0) }
 ; CHECK: attributes #47 = { allocsize(1,0) }
 ; CHECK: attributes #48 = { nosanitize_bounds }
-; CHECK: attributes #49 = { builtin }
+; CHECK: attributes #49 = { allockind("new,uninitialized") }
+; CHECK: attributes #50 = { builtin }
 
 ;; Metadata
 
 ; Metadata -- Module flags
 !llvm.module.flags = !{!0, !1, !2, !4, !5, !6}
 ; CHECK: !llvm.module.flags = !{!0, !1, !2, !4, !5, !6}
 
 !0 = !{i32 1, !"mod1", i32 0}