[llvm-dev] [cfe-dev] Zero length function pointer equality

[Hans Wennborg via llvm-dev]

Maybe we can just expand this to always apply: https://reviews.llvm.org/D32330

On Fri, Jul 24, 2020 at 2:46 AM David Blaikie via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
>
> LLVM can produce zero length functions from cases like this (when
> optimizations are enabled):
>
> void f1() { __builtin_unreachable(); }
> int f2() { /* missing return statement */ }
>
> This code is valid, so long as the functions are never called.
>
> I believe C++ requires that all functions have a distinct address (ie:
> &f1 != &f2) and LLVM optimizes code on this basis (assert(f1 == f2)
> gets optimized into an unconditional assertion failure)
>
> But these zero length functions can end up with identical addresses.
>
> I'm unaware of anything in the C++ spec (or the LLVM langref) that
> would indicate that would allow distinct functions to have identical
> addresses - so should we do something about this in the LLVM backend?
> add a little padding? a nop instruction? (if we're adding an
> instruction anyway, perhaps we might as well make it an int3?)
>
> (I came across this due to DWARF issues with zero length functions &
> thinking about if/how this should be supported)
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev