Samuel Iglesias Gonsálvez <sigles...@igalia.com> writes: > From: Iago Toral Quiroga <ito...@igalia.com> > > Because the stride is in units for the type, if we copy-propagate from > a another instruction using a larger type, then we need to make sure > that the source in that instruction, the one we will be copy-propagating > from, sources consecutive elements, otherwise, when sourced using a > a smaller type, the actual elements read would change. > > Prevents that we turn this: > mov(8) vgrf3+2.0:DF, vgrf11<0>:DF > load_payload(8) vgrf15:UD, ..., vgrf3+2.0<0>:D, vgrf3+3.0<0>:D > > Into: > mov(8) vgrf3+2.0:DF, vgrf11<0>:DF > load_payload(8) vgrf15:UD, ..., vgrf11<0>:D, vgrf11<0>:D >
Sorry but I don't see the problem, the two assembly examples look fully equivalent to me. > In the original instructions, vgrf3+2.0<0>:D reads a replicated 64-bit > value, while the result after copy propagation only reads the first > 32-bit of the value. > --- > src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp | 9 +++++++++ > 1 file changed, 9 insertions(+) > > 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 9fc06cb..f98ab41 100644 > --- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp > +++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp > @@ -400,6 +400,15 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, > acp_entry *entry) > if (type_sz(entry->dst.type) < type_sz(inst->src[arg].type)) > return false; > > + /* Bail if the instruction type is larger than the execution type of the > + * copy and the stride of the source we would be copy propagating from > + * has a stride other than 1. Otherwise, since the stride is in units of > + * the type, we would be changing the region effectively sourced. > + */ > + if (type_sz(entry->dst.type) > type_sz(inst->src[arg].type) && > + entry->src.stride != 1) > + return false; NAK, there is a more accurate condition just a few lines below making sure that the strides can be composed correctly when the original entry->src.stride is not one. Some special cases of 'type_sz(entry->dst.type) > type_sz(inst->src[arg].type) && entry->src.stride != 1' are handled by copy propagation, and the cases that are not should already be caught by the check immediately below. > + > /* Bail if the result of composing both strides cannot be expressed > * as another stride. This avoids, for example, trying to transform > * this: > -- > 2.5.0 > > _______________________________________________ > mesa-dev mailing list > mesa-dev@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/mesa-dev
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