On Thu, May 3, 2018 at 12:29 AM, Richard Biener <richard.guent...@gmail.com> wrote: > Just as a note, IIRC all the SUBREG_PROMOTED_* stuff is quite fragile > - I remember > Eric fixing things up a bit but some verification would be nice to > have (instrumentation > at RTL level that for SUBREG_PROMOTED_* the bits are as expected).
If you are using SUBREG_PROMOTED_* in a late optimization pass like combine, then this requires that all earlier optimization passes propagate the info correctly. I suppose there could be issues there. But that isn't what this patch is doing. This is code called during initial RTL generation. The SUBREG_PROMOTED_* bits are set during this process because we know that arguments are passed sign-extended to full register size. We are then consuming the info while still in the RTL generation phase. I think that there is little that can go wrong here. Verifying this info in RTL generation would effectively be verifying that the argument passing conventions are implemented correctly, and we already have other ways to do that. It might be useful to try to verify this info before combine where it is more likely to be wrong. I don't think there is any easy way to verify this at compile time. This would probably require emitting code to check at application run-time that a promoted subreg actually has a properly promoted value, and call abort if it doesn't. This would likely be an expensive check that we don't want enabled by default, but might be useful for debugging purposes. I don't think we have any --enable-checking code like this at present. We have compiler compile-time checking and compiler run-time checking, but I don't think that we have application run-time checking. This would be more like a sanitizer option, except to validate info in the RTL. Is this what you are asking for? Jim
