Attributes: add a new allocalign attribute

This will let us start moving away from hard-coded attributes in
MemoryBuiltins.cpp and put the knowledge about various attribute
functions in the compilers that emit those calls where it probably
belongs.

Differential Revision: https://reviews.llvm.org/D117921

Author: durin42

llvm/docs/LangRef.rst

@@ -1379,6 +1379,14 @@ Currently, only the following parameter attributes are defined:
     information that is not mapped to base types in the backend (for example,
     over-alignment specification through language attributes).
 
+``allocalign``
+    The function parameter marked with this attribute is is the alignment in bytes of the
+    newly allocated block returned by this function. The returned value must either have
+    the specified alignment or be the null pointer. The return value MAY be more aligned
+    than the requested alignment, but not less aligned.  Invalid (e.g. non-power-of-2)
+    alignments are permitted for the allocalign parameter, so long as the returned pointer
+    is null. This attribute may only be applied to integer parameters.
+
 .. _gc:
 
 Garbage Collector Strategy Names

llvm/include/llvm/AsmParser/LLToken.h

@@ -177,6 +177,7 @@ enum Kind {
 
   // Attributes:
   kw_attributes,
+  kw_allocalign,
   kw_allocsize,
   kw_alwaysinline,
   kw_argmemonly,

llvm/include/llvm/Bitcode/LLVMBitCodes.h

@@ -678,6 +678,7 @@ enum AttributeKindCodes {
   ATTR_KIND_ELEMENTTYPE = 77,
   ATTR_KIND_DISABLE_SANITIZER_INSTRUMENTATION = 78,
   ATTR_KIND_NO_SANITIZE_BOUNDS = 79,
+  ATTR_KIND_ALLOC_ALIGN = 80,
 };
 
 enum ComdatSelectionKindCodes {

llvm/include/llvm/IR/Attributes.td

@@ -47,6 +47,10 @@ class StrBoolAttr<string S> : Attr<S, []>;
 /// 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]>;
+
 /// 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

@@ -634,6 +634,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(attributes);
 
   KEYWORD(alwaysinline);
+  KEYWORD(allocalign);
   KEYWORD(allocsize);
   KEYWORD(argmemonly);
   KEYWORD(builtin);

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -1520,6 +1520,8 @@ static Attribute::AttrKind getAttrFromCode(uint64_t Code) {
     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_SIZE:
     return Attribute::AllocSize;
   case bitc::ATTR_KIND_NO_RED_ZONE:

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -610,6 +610,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
   switch (Kind) {
   case Attribute::Alignment:
     return bitc::ATTR_KIND_ALIGNMENT;
+  case Attribute::AllocAlign:
+    return bitc::ATTR_KIND_ALLOC_ALIGN;
   case Attribute::AllocSize:
     return bitc::ATTR_KIND_ALLOC_SIZE;
   case Attribute::AlwaysInline:

llvm/lib/IR/Attributes.cpp

@@ -1780,7 +1780,8 @@ AttributeMask AttributeFuncs::typeIncompatible(Type *Ty) {
   if (!Ty->isIntegerTy())
     // Attributes that only apply to integers.
     Incompatible.addAttribute(Attribute::SExt)
-      .addAttribute(Attribute::ZExt);
+        .addAttribute(Attribute::ZExt)
+        .addAttribute(Attribute::AllocAlign);
 
   if (!Ty->isPointerTy())
     // Attributes that only apply to pointers.

llvm/lib/Transforms/Utils/CodeExtractor.cpp

@@ -962,6 +962,7 @@ Function *CodeExtractor::constructFunction(const ValueSet &inputs,
         break;
       // These attributes cannot be applied to functions.
       case Attribute::Alignment:
+      case Attribute::AllocAlign:
       case Attribute::ByVal:
       case Attribute::Dereferenceable:
       case Attribute::DereferenceableOrNull:

llvm/test/Bitcode/compatibility.ll

@@ -560,6 +560,8 @@ declare void @f.param.swiftasync(i8* swiftasync)
 ; CHECK: declare void @f.param.swiftasync(i8* swiftasync)
 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)
 
 ; Functions -- unnamed_addr and local_unnamed_addr
 declare void @f.unnamed_addr() unnamed_addr