On Fri, 8 Jun 2012, Bin.Cheng wrote: > For example, most c programs call printf to format output data, that > means floating point code get linked even the program only want to > output non-floating point numbers. Currently, we rely on end-user to > call iprintf if the program does not want floating point.
The name "iprintf" is in the user's namespace, not the implementation namespace, so it wouldn't be a particularly good idea for the compiler to generate calls to it (certainly not in standards modes; cf. bug 46926). But as I understand it you're suggesting something more complicated than generating a call to a special function. > I noticed that GCC now can check format string of printf functions, so > I am wondering if it is possible to take advantage of this utility, by > making gcc detect whether printf prints floating point number and then > generate assembly directive in backend to pull in floating point > functions only if necessary. Obviously this won't help if the program is using functions such as vprintf to print things with variable format strings.... > The problem is: > The check is done in front end, so how should I expose the check > result to back-end. Is there any hook utility? The front end should generate appropriate GIMPLE describing semantics of the translation unit. If you are simply calling some system-defined __iprintf this is a matter of rewriting function calls (given an appropriate C-family target hook to do the rewriting). But if you want e.g. an assembler directive causing a relocation against some magic symbol to cause certain code to be linked in, you could probably generate a call to __builtin_<arch>_printf_needs_float (for example), again given a suitable hook, and then have the back end handle such a call by generating a directive rather than code. -- Joseph S. Myers jos...@codesourcery.com
