ArgumentPromotion: Drop sret attribute on functions that are only called directly.
If the first argument to a function is a 'this' argument and the second
has the sret attribute, the ArgumentPromotion pass may promote the 'this'
argument to more than one argument, violating the IR constraint that 'sret'
may only be applied to the first or second argument.
Although this IR constraint is arguably unnecessary, it highlighted the fact
that ArgPromotion does not need to preserve this attribute. Dropping the
attribute reduces register pressure in the backend by avoiding the register
copy required by sret. Because sret implies noalias, we also replace the
former with the latter.
Differential Revision: http://reviews.llvm.org/D10353
llvm-svn: 239488
diff --git a/llvm/lib/IR/Function.cpp b/llvm/lib/IR/Function.cpp
index cf8e3ed..2b439bb 100644
--- a/llvm/lib/IR/Function.cpp
+++ b/llvm/lib/IR/Function.cpp
@@ -154,10 +154,8 @@
/// it in its containing function.
bool Argument::hasStructRetAttr() const {
if (!getType()->isPointerTy()) return false;
- if (this != getParent()->arg_begin())
- return false; // StructRet param must be first param
return getParent()->getAttributes().
- hasAttribute(1, Attribute::StructRet);
+ hasAttribute(getArgNo()+1, Attribute::StructRet);
}
/// hasReturnedAttr - Return true if this argument has the returned attribute on