[IR] Since AttributeSets are sorted, binary search them.

Not likely to make a big difference, but there's a fair bit of pointer
chasing in large sets.

llvm/lib/IR/AttributeImpl.h

@@ -188,6 +188,7 @@ class AttributeSetNode final
 
   static AttributeSetNode *getSorted(LLVMContext &C,
                                      ArrayRef<Attribute> SortedAttrs);
+  Optional<Attribute> findEnumAttribute(Attribute::AttrKind Kind) const;
 
 public:
   // AttributesSetNode is uniqued, these should not be available.

llvm/lib/IR/Attributes.cpp

@@ -867,12 +867,26 @@ bool AttributeSetNode::hasAttribute(StringRef Kind) const {
   return StringAttrs.count(Kind);
 }
 
+Optional<Attribute>
+AttributeSetNode::findEnumAttribute(Attribute::AttrKind Kind) const {
+  // Do a quick presence check.
+  if (!hasAttribute(Kind))
+    return None;
+
+  // Attributes in a set are sorted by enum value, followed by string
+  // attributes. Binary search the one we want.
+  const Attribute *I =
+      std::lower_bound(begin(), end() - StringAttrs.size(), Kind,
+                       [](Attribute A, Attribute::AttrKind Kind) {
+                         return A.getKindAsEnum() < Kind;
+                       });
+  assert(I != end() && I->hasAttribute(Kind) && "Presence check failed?");
+  return *I;
+}
+
 Attribute AttributeSetNode::getAttribute(Attribute::AttrKind Kind) const {
-  if (hasAttribute(Kind)) {
-    for (const auto &I : *this)
-      if (I.hasAttribute(Kind))
-        return I;
-  }
+  if (auto A = findEnumAttribute(Kind))
+    return *A;
   return {};
 }
 
@@ -881,45 +895,39 @@ Attribute AttributeSetNode::getAttribute(StringRef Kind) const {
 }
 
 MaybeAlign AttributeSetNode::getAlignment() const {
-  for (const auto &I : *this)
-    if (I.hasAttribute(Attribute::Alignment))
-      return I.getAlignment();
+  if (auto A = findEnumAttribute(Attribute::Alignment))
+    return A->getAlignment();
   return None;
 }
 
 MaybeAlign AttributeSetNode::getStackAlignment() const {
-  for (const auto &I : *this)
-    if (I.hasAttribute(Attribute::StackAlignment))
-      return I.getStackAlignment();
+  if (auto A = findEnumAttribute(Attribute::StackAlignment))
+    return A->getStackAlignment();
   return None;
 }
 
 Type *AttributeSetNode::getByValType() const {
-  for (const auto &I : *this)
-    if (I.hasAttribute(Attribute::ByVal))
-      return I.getValueAsType();
+  if (auto A = findEnumAttribute(Attribute::ByVal))
+    return A->getValueAsType();
   return 0;
 }
 
 uint64_t AttributeSetNode::getDereferenceableBytes() const {
-  for (const auto &I : *this)
-    if (I.hasAttribute(Attribute::Dereferenceable))
-      return I.getDereferenceableBytes();
+  if (auto A = findEnumAttribute(Attribute::Dereferenceable))
+    return A->getDereferenceableBytes();
   return 0;
 }
 
 uint64_t AttributeSetNode::getDereferenceableOrNullBytes() const {
-  for (const auto &I : *this)
-    if (I.hasAttribute(Attribute::DereferenceableOrNull))
-      return I.getDereferenceableOrNullBytes();
+  if (auto A = findEnumAttribute(Attribute::DereferenceableOrNull))
+    return A->getDereferenceableOrNullBytes();
   return 0;
 }
 
 std::pair<unsigned, Optional<unsigned>>
 AttributeSetNode::getAllocSizeArgs() const {
-  for (const auto &I : *this)
-    if (I.hasAttribute(Attribute::AllocSize))
-      return I.getAllocSizeArgs();
+  if (auto A = findEnumAttribute(Attribute::AllocSize))
+    return A->getAllocSizeArgs();
   return std::make_pair(0, 0);
 }