Allow empty range attribute and add assert for full range

Author: andjo403

llvm/docs/LangRef.rst

@@ -1675,7 +1675,8 @@ Currently, only the following parameter attributes are defined:
     -  The pair ``a,b`` represents the range ``[a,b)``.
     -  Both ``a`` and ``b`` are constants.
     -  The range is allowed to wrap.
-    -  The range should not represent the full or empty set. That is, ``a!=b``.
+    -  Only for the empty set is ``a`` and ``b`` allowed to be equal and
+       only for the value 0.
 
     This attribute may only be applied to parameters or return values with integer 
     or vector of integer types.

llvm/include/llvm/IR/Attributes.h

@@ -160,6 +160,7 @@ class Attribute {
   static Attribute getWithUWTableKind(LLVMContext &Context, UWTableKind Kind);
   static Attribute getWithMemoryEffects(LLVMContext &Context, MemoryEffects ME);
   static Attribute getWithNoFPClass(LLVMContext &Context, FPClassTest Mask);
+  static Attribute getWithRange(LLVMContext &Context, const ConstantRange &CR);
 
   /// For a typed attribute, return the equivalent attribute with the type
   /// changed to \p ReplacementTy.

llvm/lib/AsmParser/LLParser.cpp

@@ -3109,8 +3109,8 @@ bool LLParser::parseRangeAttr(AttrBuilder &B) {
   if (ParseAPSInt(BitWidth, Lower) ||
       parseToken(lltok::comma, "expected ','") || ParseAPSInt(BitWidth, Upper))
     return true;
-  if (Lower == Upper)
-    return tokError("the range should not represent the full or empty set!");
+  if (Lower == Upper && !Lower.isMinValue())
+    return tokError("the range represent the empty set but limits aren't 0!");
 
   if (parseToken(lltok::rparen, "expected ')'"))
     return true;

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -2369,7 +2369,9 @@ Error BitcodeReader::parseAttributeGroupBlock() {
             return MaybeCR.takeError();
           i--;
 
-          B.addConstantRangeAttr(Kind, MaybeCR.get());
+          assert(Kind == Attribute::Range &&
+                 "Unhandled ConstantRangeAttribute");
+          B.addRangeAttr(MaybeCR.get());
         } else if (Record[i] == 8) {
           Attribute::AttrKind Kind;
 

llvm/lib/IR/Attributes.cpp

@@ -286,6 +286,12 @@ Attribute Attribute::getWithNoFPClass(LLVMContext &Context,
   return get(Context, NoFPClass, ClassMask);
 }
 
+Attribute Attribute::getWithRange(LLVMContext &Context,
+                                  const ConstantRange &CR) {
+  assert(!CR.isFullSet() && "Range must not be full!");
+  return get(Context, Range, CR);
+}
+
 Attribute
 Attribute::getWithAllocSizeArgs(LLVMContext &Context, unsigned ElemSizeArg,
                                 const std::optional<unsigned> &NumElemsArg) {
@@ -2024,7 +2030,10 @@ AttrBuilder &AttrBuilder::addConstantRangeAttr(Attribute::AttrKind Kind,
 }
 
 AttrBuilder &AttrBuilder::addRangeAttr(const ConstantRange &CR) {
-  return addConstantRangeAttr(Attribute::Range, CR);
+  if (CR.isFullSet())
+    return *this;
+
+  return addAttribute(Attribute::getWithRange(Ctx, CR));
 }
 
 AttrBuilder &

llvm/lib/IR/Core.cpp

@@ -191,11 +191,11 @@ LLVMAttributeRef LLVMCreateConstantRangeAttribute(LLVMContextRef C,
                                                   const uint64_t UpperWords[]) {
   auto &Ctx = *unwrap(C);
   auto AttrKind = (Attribute::AttrKind)KindID;
+  assert(AttrKind == Attribute::Range && "Unhandled ConstantRangeAttribute");
   unsigned NumWords = divideCeil(NumBits, 64);
-  return wrap(Attribute::get(
-      Ctx, AttrKind,
-      ConstantRange(APInt(NumBits, ArrayRef(LowerWords, NumWords)),
-                    APInt(NumBits, ArrayRef(UpperWords, NumWords)))));
+  return wrap(Attribute::getWithRange(
+      Ctx, ConstantRange(APInt(NumBits, ArrayRef(LowerWords, NumWords)),
+                         APInt(NumBits, ArrayRef(UpperWords, NumWords)))));
 }
 
 LLVMAttributeRef LLVMCreateStringAttribute(LLVMContextRef C,

llvm/test/Assembler/range-attribute-invalid-range.ll

@@ -1,6 +1,6 @@
 ; RUN: not llvm-as < %s -o /dev/null 2>&1 | FileCheck %s
 
-; CHECK: the range should not represent the full or empty set!
-define void @range_empty(i8 range(i8 0, 0) %a) {
+; CHECK: the range represent the empty set but limits aren't 0!
+define void @range_empty(i8 range(i8 1, 1) %a) {
   ret void
 }

llvm/test/Bitcode/attributes.ll

@@ -531,8 +531,8 @@ define range(i32 -1, 42) i32 @range_attribute(<4 x i32> range(i32 -1, 42) %a) {
   ret i32 0
 }
 
-; CHECK: define range(i32 0, 42) i32 @range_attribute_same_range_other_bitwidth(i8 range(i8 0, 42) %a)
-define range(i32 0, 42) i32 @range_attribute_same_range_other_bitwidth(i8 range(i8 0, 42) %a) {
+; CHECK: define range(i32 0, 0) i32 @range_attribute_same_range_other_bitwidth(i8 range(i8 0, 42) %a)
+define range(i32 0, 0) i32 @range_attribute_same_range_other_bitwidth(i8 range(i8 0, 42) %a) {
   ret i32 0
 }