A different approach to shifting Attributes forward

src/codegen.cpp

@@ -5172,24 +5172,41 @@ static Function* gen_cfun_wrapper(
  std::vector<Type*> fargt_sig(sig.fargt_sig);
 
  fargt_sig.insert(fargt_sig.begin() + sig.sret, T_pprjlvalue);
+
  // Shift LLVM attributes for parameters one to the right, as
  // we are adding the extra nest parameter after sret arg.
- // AttributeList has function attributes and return value
- // attributes before the parameter attributes.
- if (attributes.getNumAttrSets() > static_cast<unsigned>(2 + sig.sret)) {
- AttrBuilder toShift;
-  // Skip past function and return and sret attributes to the first real parameter
-  for (auto it = attributes.index_begin() + 2 + sig.sret; it != attributes.index_end(); ++it) {
-  AttrBuilder toShiftTemp(attributes.getAttributes(it));
-  attributes = attributes.removeAttributes(jl_LLVMContext, it);
- attributes = attributes.addAttributes(jl_LLVMContext, it, toShift);
- toShift = std::move(toShiftTemp);
+ std::vector<std::pair<unsigned, AttributeSet>> newAttributes;
+ newAttributes.reserve(attributes.getNumAttrSets() + 1);
+ auto it = attributes.index_begin();
+
+ // Skip past non-parameter attributes (and perhaps parameter return)
+ // Beware that function index is ~0U, so can't just replace with <
+ for (;it != attributes.index_end(); ++it) {
+ if (it != AttributeList::AttrIndex::FunctionIndex &&
+ it >= AttributeList::AttrIndex::FirstArgIndex + sig.sret) {
+ break;
  }
- attributes = attributes.addAttributes(jl_LLVMContext, attributes.index_end(), toShift);
+ newAttributes.push_back(std::make_pair(it, attributes.getAttributes(it)));
+ }
+
+ // Skip ahead to first parameter (where we may already be, but aren't necessarily)
+ it = AttributeList::AttrIndex::FirstArgIndex + sig.sret;
+
+ // Add the new nest attribute
+ AttrBuilder attrBuilder;
+ attrBuilder.addAttribute(Attribute::Nest);
+ AttributeSet set(AttributeSet::get(jl_LLVMContext, attrBuilder));
+ newAttributes.push_back(std::make_pair(it, set));
+
+ // Shift forward the rest of the attributes
+ // We are now past the magic numbers, so < is ok here.
+ for(;it < attributes.index_end(); ++it) {
+ newAttributes.push_back(std::make_pair(it + 1, attributes.getAttributes(it)));
  }
 
+ // Create the new AttributeList
+ attributes = AttributeList::get(jl_LLVMContext, newAttributes);
  functype = FunctionType::get(sig.sret ? T_void : sig.prt, fargt_sig, /*isVa*/false);
- attributes = attributes.addAttribute(jl_LLVMContext, 1 + sig.sret, Attribute::Nest);
  }
  else {
  functype = sig.functype();