[LLVMdev] [RFC] NoBuiltin Attribute

[Joerg Sonnenberger]

On Mon, Feb 18, 2013 at 06:10:48PM -0800, Chris Lattner wrote:
> Out of curiosity, how important is -fno-builtin-foo?

Depends, does that include alloca and the object size stuff?

> Isn't it enough to just have -fno-builtin-foo disable *all* builtin
> optimizations for the unit of code being compiled?  This is overly
> conservative - is that actually a problem for something?

Making -fno-builtin-foo imply -fno-builtin seems overly aggressively. I
can imagine wanting to use the former when implementing libc to get more
predictable behavior, but still wanting to get e.g. the string
optimisations.

As I mentioned on IRC, there is also the related issue of explicitly
requesting a builtin, i.e. a positive __attribute__((__builtin__)) for
freestanding code. I don't think that -fno-builtin-puts should imply
-fno-builtin-printf.  It should apply to function calls in this module,
but may be merged by adding the nobuiltin attribute to the prototypes in
all other modules during LTO.

Joerg