[Attributes] Support int attributes with zero value

This regularly comes up as a stumbling stone when adding int
attributes: They currently need to be encoded in a way to avoids
the zero value.

This adds support for zero-value int attributes by a) making the
ctor determine int/enum attribute based on attribute kind, not
whether the value is non-zero and b) switching getRawIntAttr()
to return an Optional, so that it's possible to distinguish a zero
value from non-existence.

Differential Revision: https://reviews.llvm.org/D135572

1 files changed, 13 insertions, 9 deletions

diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index cbd299c..256d81f 100644
--- a/llvm/lib/IR/Attributes.cpp
+++ b/llvm/lib/IR/Attributes.cpp
@@ -89,15 +89,17 @@ unpackVScaleRangeArgs(uint64_t Value) {
 
 Attribute Attribute::get(LLVMContext &Context, Attribute::AttrKind Kind,
                          uint64_t Val) {
-  if (Val)
-    assert(Attribute::isIntAttrKind(Kind) && "Not an int attribute");
-  else
-    assert(Attribute::isEnumAttrKind(Kind) && "Not an enum attribute");
+  bool IsIntAttr = Attribute::isIntAttrKind(Kind);
+  assert((IsIntAttr || Attribute::isEnumAttrKind(Kind)) &&
+         "Not an enum or int attribute");
 
   LLVMContextImpl *pImpl = Context.pImpl;
   FoldingSetNodeID ID;
   ID.AddInteger(Kind);
-  if (Val) ID.AddInteger(Val);
+  if (IsIntAttr)
+    ID.AddInteger(Val);
+  else
+    assert(Val == 0 && "Value must be zero for enum attributes");
 
   void *InsertPoint;
   AttributeImpl *PA = pImpl->AttrsSet.FindNodeOrInsertPos(ID, InsertPoint);
@@ -105,7 +107,7 @@ Attribute Attribute::get(LLVMContext &Context, Attribute::AttrKind Kind,
   if (!PA) {
     // If we didn't find any existing attributes of the same shape then create a
     // new one and insert it.
-    if (!Val)
+    if (!IsIntAttr)
       PA = new (pImpl->Alloc) EnumAttributeImpl(Kind);
     else
       PA = new (pImpl->Alloc) IntAttributeImpl(Kind, Val);
@@ -1638,10 +1640,12 @@ AttrBuilder &AttrBuilder::removeAttribute(StringRef A) {
   return *this;
 }
 
-uint64_t AttrBuilder::getRawIntAttr(Attribute::AttrKind Kind) const {
+Optional<uint64_t> AttrBuilder::getRawIntAttr(Attribute::AttrKind Kind) const {
   assert(Attribute::isIntAttrKind(Kind) && "Not an int attribute");
   Attribute A = getAttribute(Kind);
-  return A.isValid() ? A.getValueAsInt() : 0;
+  if (A.isValid())
+    return A.getValueAsInt();
+  return None;
 }
 
 AttrBuilder &AttrBuilder::addRawIntAttr(Attribute::AttrKind Kind,
@@ -1650,7 +1654,7 @@ AttrBuilder &AttrBuilder::addRawIntAttr(Attribute::AttrKind Kind,
 }
 
 std::pair<unsigned, Optional<unsigned>> AttrBuilder::getAllocSizeArgs() const {
-  return unpackAllocSizeArgs(getRawIntAttr(Attribute::AllocSize));
+  return unpackAllocSizeArgs(getRawIntAttr(Attribute::AllocSize).value_or(0));
 }
 
 AttrBuilder &AttrBuilder::addAlignmentAttr(MaybeAlign Align) {