Add remove method to operate on AttrBuilder instead of AttributeSet.

Prior to this change we would have to construct a temporary AttributeSet (which isn't temporary at all given that its allocated on the context), just to contain the attributes in the builder, then call remove on that.

Now we can just remove any attributes from the (lightweight and really temporary) builder itself.

Will be used in a future commit to remove some temporary attributes sets.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236666 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/Attributes.h

@@ -289,6 +289,12 @@ public:
   AttributeSet removeAttributes(LLVMContext &C, unsigned Index, 
                                 AttributeSet Attrs) const;
 
+  /// \brief Remove the specified attributes at the specified index from this
+  /// attribute list. Because attribute lists are immutable, this returns the
+  /// new list.
+  AttributeSet removeAttributes(LLVMContext &C, unsigned Index,
+                                const AttrBuilder &Attrs) const;
+
   /// \brief Add the dereferenceable attribute to the attribute set at the given
   /// index. Since attribute sets are immutable, this returns a new set.
   AttributeSet addDereferenceableAttr(LLVMContext &C, unsigned Index,
@@ -464,6 +470,13 @@ public:
   /// \brief Add the attributes from the builder.
   AttrBuilder &merge(const AttrBuilder &B);
 
+  /// \brief Remove the attributes from the builder.
+  AttrBuilder &remove(const AttrBuilder &B);
+
+  /// \brief \brief Return true if the builder has any attribute that's in the
+  /// specified builder.
+  bool overlaps(const AttrBuilder &B) const;
+
   /// \brief Return true if the builder has the specified attribute.
   bool contains(Attribute::AttrKind A) const {
     assert((unsigned)A < Attribute::EndAttrKinds && "Attribute out of range!");

lib/IR/Attributes.cpp

@@ -857,6 +857,42 @@ AttributeSet AttributeSet::removeAttributes(LLVMContext &C, unsigned Index,
   return get(C, AttrSet);
 }
 
+AttributeSet AttributeSet::removeAttributes(LLVMContext &C, unsigned Index,
+                                            const AttrBuilder &Attrs) const {
+  if (!pImpl) return AttributeSet();
+
+  // FIXME it is not obvious how this should work for alignment.
+  // For now, say we can't pass in alignment, which no current use does.
+  assert(!Attrs.hasAlignmentAttr() && "Attempt to change alignment!");
+
+  // Add the attribute slots before the one we're trying to add.
+  SmallVector<AttributeSet, 4> AttrSet;
+  uint64_t NumAttrs = pImpl->getNumAttributes();
+  AttributeSet AS;
+  uint64_t LastIndex = 0;
+  for (unsigned I = 0, E = NumAttrs; I != E; ++I) {
+    if (getSlotIndex(I) >= Index) {
+      if (getSlotIndex(I) == Index) AS = getSlotAttributes(LastIndex++);
+      break;
+    }
+    LastIndex = I + 1;
+    AttrSet.push_back(getSlotAttributes(I));
+  }
+
+  // Now remove the attribute from the correct slot. There may already be an
+  // AttributeSet there.
+  AttrBuilder B(AS, Index);
+  B.remove(Attrs);
+
+  AttrSet.push_back(AttributeSet::get(C, Index, B));
+
+  // Add the remaining attribute slots.
+  for (unsigned I = LastIndex, E = NumAttrs; I < E; ++I)
+    AttrSet.push_back(getSlotAttributes(I));
+
+  return get(C, AttrSet);
+}
+
 AttributeSet AttributeSet::addDereferenceableAttr(LLVMContext &C, unsigned Index,
                                                   uint64_t Bytes) const {
   llvm::AttrBuilder B;
@@ -1211,15 +1247,52 @@ AttrBuilder &AttrBuilder::merge(const AttrBuilder &B) {
   if (!DerefBytes)
     DerefBytes = B.DerefBytes;
 
+  if (!DerefOrNullBytes)
+    DerefOrNullBytes = B.DerefOrNullBytes;
+
   Attrs |= B.Attrs;
 
-  for (td_const_iterator I = B.TargetDepAttrs.begin(),
-         E = B.TargetDepAttrs.end(); I != E; ++I)
-    TargetDepAttrs[I->first] = I->second;
+  for (auto I : B.td_attrs())
+    TargetDepAttrs[I.first] = I.second;
 
   return *this;
 }
 
+AttrBuilder &AttrBuilder::remove(const AttrBuilder &B) {
+  // FIXME: What if both have alignments, but they don't match?!
+  if (B.Alignment)
+    Alignment = 0;
+
+  if (B.StackAlignment)
+    StackAlignment = 0;
+
+  if (B.DerefBytes)
+    DerefBytes = 0;
+
+  if (B.DerefOrNullBytes)
+    DerefOrNullBytes = 0;
+
+  Attrs &= ~B.Attrs;
+
+  for (auto I : B.td_attrs())
+    TargetDepAttrs.erase(I.first);
+
+  return *this;
+}
+
+bool AttrBuilder::overlaps(const AttrBuilder &B) const {
+  // First check if any of the target independent attributes overlap.
+  if ((Attrs & B.Attrs).any())
+    return true;
+
+  // Then check if any target dependent ones do.
+  for (auto I : td_attrs())
+    if (B.contains(I.first))
+      return true;
+
+  return false;
+}
+
 bool AttrBuilder::contains(StringRef A) const {
   return TargetDepAttrs.find(A) != TargetDepAttrs.end();
 }