[IR] Make AttributeSetNode public, avoid temporary AttributeList copies

Summary:
AttributeList::get(Fn|Ret|Param)Attributes no longer creates a temporary
AttributeList just to hide the AttributeSetNode type.

I've also added a factory method to create AttributeLists from a
parallel array of AttributeSetNodes. I think this simplifies
construction of AttributeLists when rewriting function prototypes.
Previously we would test if a particular index had attributes, and
conditionally add a temporary attribute list to a vector. Now the
attribute set vector is parallel to the argument vector already that
these passes already construct.

My long term vision is to wrap AttributeSetNode* inside an AttributeSet
type that holds the enum attributes, but that will come in a follow up
change.

I haven't done any performance measurements for this change because
profiling hasn't shown that any of the affected code is hot.

Reviewers: pete, chandlerc, sanjoy, hfinkel

Reviewed By: pete

Subscribers: jfb, llvm-commits

Differential Revision: https://reviews.llvm.org/D31198

llvm-svn: 299875

1 files changed, 1 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index dc7390232c5..5d41ca9f9fc 100644
--- a/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -439,8 +439,7 @@ void MergeFunctions::replaceDirectCallers(Function *Old, Function *New) {
           Context, AttributeList::ReturnIndex, NewFuncAttrs.getRetAttributes());
 
       for (unsigned argIdx = 0; argIdx < CS.arg_size(); argIdx++) {
-        AttributeList Attrs = NewFuncAttrs.getParamAttributes(argIdx);
-        if (Attrs.getNumSlots())
+        if (AttributeSetNode *Attrs = NewFuncAttrs.getParamAttributes(argIdx))
           CallSiteAttrs = CallSiteAttrs.addAttributes(Context, argIdx, Attrs);
       }