[Mesa-dev] [PATCH 1/2] i965/vec4: Change types as needed to propagate source modifiers using current instruction

[Alejandro Piñeiro]

SEL and MOV instructions, as long as they don't have source modifiers, are
just copying bits around.  So those kind of instruction could be propagated
even if there are type mismatches. This is needed because NIR generates
integer SEL and MOV instructions whenever it doesn't know what else to
generate.

This commit adds support for copy propagation using current instruction
as reference.

v2: check saturate too, as suggested by Jason Ekstrand
---

 .../drivers/dri/i965/brw_vec4_copy_propagation.cpp | 28 ++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
index 5a15eb8..6cd6f4f 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
@@ -249,6 +249,16 @@ try_constant_propagate(const struct brw_device_info *devinfo,
 }
 
 static bool
+can_change_source_types(vec4_instruction *inst)
+{
+   return !inst->src[0].abs && !inst->src[0].negate && !inst->saturate &&
+      (inst->opcode == BRW_OPCODE_MOV ||
+       (inst->opcode == BRW_OPCODE_SEL &&
+        inst->predicate != BRW_PREDICATE_NONE &&
+        !inst->src[1].abs && !inst->src[1].negate));
+}
+
+static bool
 try_copy_propagate(const struct brw_device_info *devinfo,
                    vec4_instruction *inst,
                    int arg, struct copy_entry *entry)
@@ -308,7 +318,9 @@ try_copy_propagate(const struct brw_device_info *devinfo,
         value.swizzle != BRW_SWIZZLE_XYZW) && !inst->can_do_source_mods(devinfo))
       return false;
 
-   if (has_source_modifiers && value.type != inst->src[arg].type)
+   if (has_source_modifiers &&
+       value.type != inst->src[arg].type &&
+       !can_change_source_types(inst))
       return false;
 
    if (has_source_modifiers &&
@@ -362,7 +374,19 @@ try_copy_propagate(const struct brw_device_info *devinfo,
       }
    }
 
-   value.type = inst->src[arg].type;
+   if (has_source_modifiers &&
+       value.type != inst->src[arg].type) {
+      /* We are propagating source modifiers from a MOV with a different
+       * type.  If we got here, then we can just change the source and
+       * destination types of the instruction and keep going.
+       */
+      assert(can_change_source_types(inst));
+      for (int i = 0; i < 3; i++) {
+         inst->src[i].type = value.type;
+      }
+      inst->dst.type = value.type;
+   } else
+      value.type = inst->src[arg].type;
    inst->src[arg] = value;
    return true;
 }
-- 
2.1.4