[LLVMdev] [RFC] NoBuiltin Attribute

[Krzysztof Parzyszek]

On 2/19/2013 12:26 PM, Chris Lattner wrote:
>
> void foo() {
>    auto fp = printf;
>    fp("xyz\n");
> }
>
> With -fno-builtin-printf, we can't optimize the call to printf, even though it only becomes apparent after (trivial) devirtualization.

Ha.  Good example.
What would you expect to happen in this case?

--- a.cpp ---  (with -fno-builtin-printf)
pointer fptr;
void foo(bool x) {
   bar(x);
}
void set(bool x) {
   if (x) fptr = printf;
   else   fptr = vprintf;
}
-------------

--- b.cpp ---  (no restrictions)
extern pointer fptr;
void bar(bool x) {
   set(x);
   va_list ap = ...
   (*fptr)("haha", ap);
}
-------------

Also, with the options reversed.

-Krzysztof

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