[Mesa-dev] [PATCH 04/23] i965/fs: fix requirements to allow type change in copy-propagation

[Samuel Iglesias Gonsálvez]

From: Iago Toral Quiroga <itoral at igalia.com>

When source modifiers are present and the types of the source and
the entry's source are different, there are certain cases in which
we allow copy-propagation to change the type of source by the type
of the entry's source we are copy propagating from.

However, it is not generally safe to do this if the types involved
have different sizes, since parameters like the stride would change
the semantics of the resulting instruction.

Prevents that we turn this:

load_payload(8) vgrf17:DF, |vgrf4+0.0|:DF 1sthalf
mov(8) vgrf18:DF, vgrf17:DF 1sthalf
load_payload(8) vgrf5:DF, vgrf18:DF, vgrf20:DF NoMask 1sthalf WE_all
load_payload(8) vgrf21:UD, vgrf5+0.4<2>:UD 1sthalf
mov(8) vgrf22:UD, vgrf21:UD 1sthalf

into:

load_payload(8) vgrf17:DF, |vgrf4+0.0|:DF 1sthalf
mov(8) vgrf18:DF, |vgrf4+0.0|:DF 1sthalf
load_payload(8) vgrf5:DF, |vgrf4+0.0|:DF, |vgrf4+2.0|:DF NoMask 1sthalf WE_all
load_payload(8) vgrf21:UD, vgrf5+0.4<2>:UD 1sthalf
mov(8) vgrf22:DF, |vgrf4+0.4|<2>:DF 1sthalf

where the semantics of the last instruccion have changed.
---
 src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

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 abc68c8..aa4c9c9 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
@@ -411,8 +411,9 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
       return false;
 
    if (has_source_modifiers &&
-       entry->dst.type != inst->src[arg].type &&
-       !inst->can_change_types())
+       ((entry->dst.type != inst->src[arg].type &&
+         !inst->can_change_types()) ||
+        (type_sz(entry->dst.type) != type_sz(inst->src[arg].type))))
       return false;
 
    if (devinfo->gen >= 8 && (entry->src.negate || entry->src.abs) &&
-- 
2.5.0