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``.
+    -  The empty range is represented using ``0,0``.
+    -  Otherwise, ``a`` and ``b` are not allowed to be equal.
 
     This attribute may only be applied to parameters or return values with integer 
     or vector of integer types.

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.isZero())
+    return tokError("the range represent the empty set but limits aren't 0!");
 
   if (parseToken(lltok::rparen, "expected ')'"))
     return true;

llvm/lib/IR/Attributes.cpp

@@ -171,6 +171,7 @@ Attribute Attribute::get(LLVMContext &Context, Attribute::AttrKind Kind,
                          const ConstantRange &CR) {
   assert(Attribute::isConstantRangeAttrKind(Kind) &&
          "Not a ConstantRange attribute");
+  assert(!CR.isFullSet() && "ConstantRange attribute must not be full");
   LLVMContextImpl *pImpl = Context.pImpl;
   FoldingSetNodeID ID;
   ID.AddInteger(Kind);
@@ -2020,6 +2021,9 @@ AttrBuilder &AttrBuilder::addInAllocaAttr(Type *Ty) {
 
 AttrBuilder &AttrBuilder::addConstantRangeAttr(Attribute::AttrKind Kind,
                                                const ConstantRange &CR) {
+  if (CR.isFullSet())
+    return *this;
+
   return addAttribute(Attribute::get(Ctx, Kind, CR));
 }
 

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
 }