On Thu, Jan 18, 2018 at 12:39:05PM -0600, Segher Boessenkool wrote: > On Wed, Jan 17, 2018 at 06:40:12PM -0500, Michael Meissner wrote: > > On Wed, Jan 17, 2018 at 04:09:57PM -0600, Segher Boessenkool wrote: > > > On Tue, Jan 16, 2018 at 10:55:43PM -0500, Michael Meissner wrote: > > > > PR target/83862 pointed out a problem I put into the 128-bit floating > > > > point > > > > type signbit optimization. The issue is we want to avoid doing a load > > > > to a > > > > floating point/vector register and then a direct move to do signbit, so > > > > we > > > > change the load to load the upper 64-bits of the floating point value > > > > to get > > > > the sign bit. Unfortunately, if the type is IEEE 128-bit and memory is > > > > addressed with an indexed address on a little endian system, it > > > > generates an > > > > illegal address and generates an internal compiler error. > > > > > > So all this is caused by these splitters running after reload. Why do > > > we have to do that? Do we? We should be able to just change it to a > > > subreg and shift, early already? > > > > The part that is failing is trying to optimize the case: > > > > x = signbit (*p) > > > > Doing the code with just registers means that you will get: > > > > vr = load *p > > gr = diret move from vr > > shift > > > > With the optimization you get: > > > > gr = 'upper' word > > shift > > > > If the address is: > > > > base + index > > > > In little endian, the compiler tried to generate: > > > > (base + index) + 8 > > > > And it didn't have a temporary register to put base+index. > > Yes, but you won't have this problem if you do this before RA. Is there > any good reason to do it only after RA?
Yes you will, because it is a memory address not a register. > If you do it before RA you immediately get > > some_di = load upper from *p > shift > > just as you want (and things might even be optimised further). And in my experience, splitting such loads and changing the type before RA, often times leads to error. -- Michael Meissner, IBM IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA email: meiss...@linux.vnet.ibm.com, phone: +1 (978) 899-4797
