[cfe-dev] Callee declarations and explicit casts

[John McCall]

On Sep 13, 2011, at 4:08 PM, John McCall wrote:
> Author: rjmccall
> Date: Tue Sep 13 18:08:34 2011
> New Revision: 139659
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=139659&view=rev
> Log:
> In general, don't look through explicit casts when trying
> to find the called declaration.  Explicit casts can radically
> change the semantics of a call, and it's no longer really a
> builtin call any more than it would be a builtin call if you stored
> the function pointer into a variable and called that.

I wanted to raise this issue here, partly to gain greater visibility
and partly to gauge people's opinions.  This commit arose out of
an IR generation bug (which I fixed separately in r139657) where
IR generation was assuming that the semantics of making a call
to a function were the same whether you evaluated the callee
normally or whether you evaluated it by directly taking the
address of the function.  Obviously, this is not true in the presence
of explicit casts.

Now, it struck me (and Doug) as pretty suspect for getCalleeDecl()
to ever look through an explicit cast, precisely because that's a
potentially very important change in the call behavior.  Ergo, this
change.  However, this is clearly a balance between clients who
really don't care about explicit casts (and therefore would prefer
getCalleeDecl() to look through them) and clients who haven't
considered whether their analysis is reasonable in the face of
explicit casts (and therefore would probably prefer
getCalleeDecl() to not look through them).

So consider this an opportunity to register your opinion and maybe
get this changed back.

John.