Attributes: add a new `allocptr` attribute

This continues the push away from hard-coded knowledge about functions
towards attributes. We'll use this to annotate free(), realloc() and
cousins and obviate the hard-coded list of free functions.

Differential Revision: https://reviews.llvm.org/D123083

llvm/docs/LangRef.rst

@@ -1392,6 +1392,13 @@ Currently, only the following parameter attributes are defined:
     alignments are permitted for the allocalign parameter, so long as the returned pointer
     is null. This attribute may only be applied to integer parameters.
 
+``allocptr``
+    The function parameter marked with this attribute is the pointer
+    that will be manipulated by the allocator. For a realloc-like
+    function the pointer will be invalidated upon success (but the
+    same address may be returned), for a free-like function the
+    pointer will always be invalidated.
+
 .. _gc:
 
 Garbage Collector Strategy Names

llvm/include/llvm/AsmParser/LLToken.h

@@ -199,6 +199,7 @@ enum Kind {
   kw_inreg,
   kw_jumptable,
   kw_minsize,
+  kw_allocptr,
   kw_naked,
   kw_nest,
   kw_noalias,

llvm/include/llvm/Bitcode/LLVMBitCodes.h

@@ -683,6 +683,7 @@ enum AttributeKindCodes {
   ATTR_KIND_DISABLE_SANITIZER_INSTRUMENTATION = 78,
   ATTR_KIND_NO_SANITIZE_BOUNDS = 79,
   ATTR_KIND_ALLOC_ALIGN = 80,
+  ATTR_KIND_ALLOCATED_POINTER = 81,
 };
 
 enum ComdatSelectionKindCodes {

llvm/include/llvm/IR/Attributes.td

@@ -51,6 +51,9 @@ def Alignment : IntAttr<"align", [ParamAttr, RetAttr]>;
 /// aligned_alloc and aligned ::operator::new.
 def AllocAlign: EnumAttr<"allocalign", [ParamAttr]>;
 
+/// Parameter is the pointer to be manipulated 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]>;

llvm/lib/AsmParser/LLLexer.cpp

@@ -652,6 +652,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(inreg);
   KEYWORD(jumptable);
   KEYWORD(minsize);
+  KEYWORD(allocptr);
   KEYWORD(naked);
   KEYWORD(nest);
   KEYWORD(noalias);

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -1538,6 +1538,8 @@ static Attribute::AttrKind getAttrFromCode(uint64_t Code) {
     return Attribute::AllocAlign;
   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:

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -647,6 +647,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     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::Naked:
     return bitc::ATTR_KIND_NAKED;
   case Attribute::Nest:

llvm/lib/IR/Attributes.cpp

@@ -1803,7 +1803,8 @@ AttributeMask AttributeFuncs::typeIncompatible(Type *Ty,
           .addAttribute(Attribute::ByVal)
           .addAttribute(Attribute::StructRet)
           .addAttribute(Attribute::ByRef)
-          .addAttribute(Attribute::ElementType);
+          .addAttribute(Attribute::ElementType)
+          .addAttribute(Attribute::AllocatedPointer);
   }
 
     // Attributes that only apply to pointers or vectors of pointers.

llvm/lib/Transforms/Utils/CodeExtractor.cpp

@@ -963,6 +963,7 @@ Function *CodeExtractor::constructFunction(const ValueSet &inputs,
         break;
       // These attributes cannot be applied to functions.
       case Attribute::Alignment:
+      case Attribute::AllocatedPointer:
       case Attribute::AllocAlign:
       case Attribute::ByVal:
       case Attribute::Dereferenceable:

llvm/test/Bitcode/compatibility.ll

@@ -562,6 +562,8 @@ declare void @f.param.swifterror(i8** swifterror)
 ; CHECK: declare void @f.param.swifterror(i8** swifterror)
 declare void @f.param.allocalign(i32 allocalign)
 ; CHECK: declare void @f.param.allocalign(i32 allocalign)
+declare void @f.param.allocptr(i32* allocptr)
+; CHECK: declare void @f.param.allocptr(i32* allocptr)
 
 ; Functions -- unnamed_addr and local_unnamed_addr
 declare void @f.unnamed_addr() unnamed_addr