Intrinsics for signed arithmetic with well-defined overflow/underflow?

Clang Frontend
1

Hi cfe-dev,

I'm doing a bit of a crazy project where I compile an IR to
'Clang-flavored C99'. The IR guarantees sane overflow/underflow
semantics for signed arithmetic, but as far as I can tell, Clang
doesn't (which is in line with the standard). Does Clang provide any
intrinsics to achieve this, which the optimizers in LLVM will respect?

Thanks!

Regards,
Alex

2

What exactly does "sane" mean, in your context? If you want wrapping,
you can just write (int)((unsigned)x+(unsigned)y).

-Eli

3

-fwrapv should permit signed overflow as well, just like in GCC. Not sure if we pass this flag all the way down, but a quick look at CodeGen does look like we're using the same Add as unsigned integers when -fwrapv is passed.

Jordan

4

Wrapping is indeed the behavior I'd like.

It does look like -fwrapv will do the job without any casts, so I'll
try with that.

Thanks folks!

Regards,
Alex