On Fri, Apr 3, 2015 at 2:06 PM, Jason Ekstrand <ja...@jlekstrand.net> wrote: > There can be problems with floats and conditional modifiers when > copy-propagating a negated UD source. Previously, we checked the source to > be copied for the negate and then checked the source being propagated to for > the type. This isn't quite what we want because we are really just looking > for negated UD sources. A check later in the file ensures that both ends > of the propagate have the right type so it works. However, if we relax the > restriction that both ends of the propagation have the same type, it ends > up causing us to bail early in cases we don't want. > --- > src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp > b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp > index 764741d..e8d092c 100644 > --- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp > +++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp > @@ -307,7 +307,7 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, > acp_entry *entry) > * instead. See also resolve_ud_negate() and comment in > * fs_generator::generate_code. > */ > - if (inst->src[arg].type == BRW_REGISTER_TYPE_UD && > + if (entry->src.type == BRW_REGISTER_TYPE_UD && > entry->src.negate) > return false; > > --
I think the claim is that we're mistakenly preventing something like mov tmp:D, -src:D cmp ..., tmp:UD, ... from being handled by copy propagation? If it were propagated, it would turn into cmp ..., -src:UD, ... (By the way, an example like this in the commit message would make review a lot easier) Same page so far? As far as I can tell that transformation would be wrong. As I understand it, negating a UD value generates a value that potentially needs 33 bits to represent, and the comparison handles that temporary value properly, but if you negate and copy to a register (like the mov is doing) you lose the top bit. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
