On Oct 24, 2012, at 7:37 PM, John McCall <[email protected]> wrote: > On Oct 24, 2012, at 7:06 PM, Bill Wendling wrote: >> Yeah. I realize the text of the warning wasn't super. I'm rethinking the >> whole patch though. As it turns out, people write bad ASM all the time, like >> >> asm("foo %0", "=r" :); >> >> I don't know if it's profitable to warn in this situation or the like. > > We actually reject that as syntactically ill-formed. :) > As we should. But it's used a lot, for instance in our tests: tools/clang/test/CodeGen/mult-alt-x86.c. :-)
> I'm not totally sure what your example is getting at. Trying to guess, if > you mean that people use asm constraints that aren't consistent with how the > assembly is used — e.g. if they use an =r constraint and then obviously rely > on the existing value in that register in the assembly — then by all means > warn about that. It needs to be under a warning flag, of course, so that > people can suppress it if they're really sure they know what they're doing; > and of course it's going to be even more false-positive-prone than a normal > warning, because assembly is not semantically rich, so you'd need to watch > out for (say) idioms that technically read the value but actually don't > depend on it in any way (like xor %0, %0). But if you're seriously > interested in putting the time into making a high-quality warning there, I > think that could be very valuable for users who do rely on inline asm. > That's basically what I'm getting at, yes. Why I reverted the patch was because it needs to be thought through a bit more before I and I assume others are happy with it. :) -bw _______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
