[LLVM] Accept noundef attribute in function definitions/calls

The `noundef` attribute indicates an argument or return value which
may never have an undef value representation.

This patch allows LLVM to parse the attribute.

Differential Revision: https://reviews.llvm.org/D83412

include/llvm/Bitcode/LLVMBitCodes.h

@@ -643,6 +643,7 @@ enum AttributeKindCodes {
   ATTR_KIND_PREALLOCATED = 65,
   ATTR_KIND_NO_MERGE = 66,
   ATTR_KIND_NULL_POINTER_IS_VALID = 67,
+  ATTR_KIND_NOUNDEF = 68,
 };
 
 enum ComdatSelectionKindCodes {

include/llvm/IR/Attributes.td

@@ -39,6 +39,9 @@ def Builtin : EnumAttr<"builtin">;
 /// Pass structure by value.
 def ByVal : TypeAttr<"byval">;
 
+/// Parameter or return value may not contain uninitialized or poison bits.
+def NoUndef : EnumAttr<"noundef">;
+
 /// Marks function as being in a cold path.
 def Cold : EnumAttr<"cold">;
 

lib/AsmParser/LLLexer.cpp

@@ -664,6 +664,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(noreturn);
   KEYWORD(nosync);
   KEYWORD(nocf_check);
+  KEYWORD(noundef);
   KEYWORD(nounwind);
   KEYWORD(null_pointer_is_valid);
   KEYWORD(optforfuzzing);

lib/AsmParser/LLParser.cpp

@@ -1374,6 +1374,7 @@ bool LLParser::ParseFnAttributeValuePairs(AttrBuilder &B,
     case lltok::kw_inalloca:
     case lltok::kw_nest:
     case lltok::kw_noalias:
+    case lltok::kw_noundef:
     case lltok::kw_nocapture:
     case lltok::kw_nonnull:
     case lltok::kw_returned:
@@ -1677,6 +1678,9 @@ bool LLParser::ParseOptionalParamAttrs(AttrBuilder &B) {
     case lltok::kw_inalloca:        B.addAttribute(Attribute::InAlloca); break;
     case lltok::kw_inreg:           B.addAttribute(Attribute::InReg); break;
     case lltok::kw_nest:            B.addAttribute(Attribute::Nest); break;
+    case lltok::kw_noundef:
+      B.addAttribute(Attribute::NoUndef);
+      break;
     case lltok::kw_noalias:         B.addAttribute(Attribute::NoAlias); break;
     case lltok::kw_nocapture:       B.addAttribute(Attribute::NoCapture); break;
     case lltok::kw_nofree:          B.addAttribute(Attribute::NoFree); break;
@@ -1774,6 +1778,9 @@ bool LLParser::ParseOptionalReturnAttrs(AttrBuilder &B) {
     }
     case lltok::kw_inreg:           B.addAttribute(Attribute::InReg); break;
     case lltok::kw_noalias:         B.addAttribute(Attribute::NoAlias); break;
+    case lltok::kw_noundef:
+      B.addAttribute(Attribute::NoUndef);
+      break;
     case lltok::kw_nonnull:         B.addAttribute(Attribute::NonNull); break;
     case lltok::kw_signext:         B.addAttribute(Attribute::SExt); break;
     case lltok::kw_zeroext:         B.addAttribute(Attribute::ZExt); break;

lib/AsmParser/LLToken.h

@@ -196,6 +196,7 @@ enum Kind {
   kw_naked,
   kw_nest,
   kw_noalias,
+  kw_noundef,
   kw_nobuiltin,
   kw_nocapture,
   kw_noduplicate,

lib/Bitcode/Reader/BitcodeReader.cpp

@@ -1530,6 +1530,8 @@ static Attribute::AttrKind getAttrFromCode(uint64_t Code) {
     return Attribute::SanitizeMemTag;
   case bitc::ATTR_KIND_PREALLOCATED:
     return Attribute::Preallocated;
+  case bitc::ATTR_KIND_NOUNDEF:
+    return Attribute::NoUndef;
   }
 }
 

lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -731,6 +731,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_SANITIZE_MEMTAG;
   case Attribute::Preallocated:
     return bitc::ATTR_KIND_PREALLOCATED;
+  case Attribute::NoUndef:
+    return bitc::ATTR_KIND_NOUNDEF;
   case Attribute::EndAttrKinds:
     llvm_unreachable("Can not encode end-attribute kinds marker.");
   case Attribute::None:

lib/IR/Attributes.cpp

@@ -443,6 +443,8 @@ std::string Attribute::getAsString(bool InAttrGrp) const {
     return "cold";
   if (hasAttribute(Attribute::ImmArg))
     return "immarg";
+  if (hasAttribute(Attribute::NoUndef))
+    return "noundef";
 
   if (hasAttribute(Attribute::ByVal)) {
     std::string Result;

lib/Transforms/Utils/CodeExtractor.cpp

@@ -877,6 +877,7 @@ Function *CodeExtractor::constructFunction(const ValueSet &inputs,
       case Attribute::NoMerge:
       case Attribute::NoReturn:
       case Attribute::NoSync:
+      case Attribute::NoUndef:
       case Attribute::None:
       case Attribute::NonNull:
       case Attribute::Preallocated:

test/Bitcode/attributes.ll

@@ -386,6 +386,12 @@ define void @f65() null_pointer_is_valid
   ret void;
 }
 
+; CHECK: define noundef i32 @f66(i32 noundef %a)
+define noundef i32 @f66(i32 noundef %a)
+{
+  ret i32 %a
+}
+
 ; CHECK: attributes #0 = { noreturn }
 ; CHECK: attributes #1 = { nounwind }
 ; CHECK: attributes #2 = { readnone }