(It appears I accidentally dropped the mailing list) Hi,
> On 08/19/2015 02:38 PM, DJ Delorie wrote: > > I've seen this on other targets too, sometimes so bad I write a quick > > target-specific "stupid move optimizer" pass to clean it up. > > > > A generic pass would be much harder, but very useful. > More important is to determine *why* we're getting these patterns. In > the IRA/LRA world, they should be a lot less common. > > Jeff AFAIU LRA is less likely to remove the moves if it didn't introduce itself. In one specific MIPS case for 64-bit, the moves are inserted for the sign-extension but IRA spills some of the allocnos and assigns different hard register for the output operand in the move as the initial register is call clobbered and the move proves to be difficult to remove later. I found tricky to remove the move in the register allocator and my current approach is to exploit the regname pass to link some of the chains and rename the input registers to turn the move into a no-op as Matthew already mentioned. I agree that it would be ideal to do the right thing in IRA/LRA but the heuristic is sensitive to changes. Regards, Robert
