On Thu, 2008-01-10 at 19:16 -0500, DJ Delorie wrote: > IIRC, the bug happened building either libgcc or newlib. If you want > to revert my latest patch in a local source tree and just try a build, > it's likely to show you an example ;-)
It was unwind-dw2.c in the m32cm libgcc multilib. The problem lies with the var-tracking pass. It sees a QImode variable being held in an HImode hard-reg, and decides to track only the low QImode part. This happens in track_loc_p, when it decides to use DECL_MODE instead of the hard reg mode. We then have to create RTL to represent the part that we are tracking, which means we have to create an invalid QImode lowpart of a hard reg that can't hold QImode values. Since we will only use this for emitting debug info this seems perfectly harmless. Unfortunately, this does mean that HARD_REGNO_NREGS must work correctly for invalid register modes. We need that info in order to construct the lowpart/subreg. Nowhere does var-tracking check to see if it is creating a valid register references, nor do I think this is necessary. Hence, I now believe that your suggested doc change is correct, and is OK to check in to mainline. -- Jim Wilson, GNU Tools Support, http://www.specifix.com
