[Mesa-dev] [PATCH v2 2/3] i965/fs: Change SEL and MOV types as needed to propagate source modifiers

[Jason Ekstrand]

SEL and MOV instructions, as long as they don't have source modifiers, are
just copying bits around.  This commit adds support to copy propagation to
switch the type of a SEL or MOV instruction as needed so that it can
propagate source modifiers.  This is needed because NIR generates integer
SEL and MOV instructions whenver it doesn't know what else to generate.

shader-db results with NIR:
total FS instructions in shared programs: 4360910 -> 4360186 (-0.02%)
FS instructions in affected programs:     59094 -> 58370 (-1.23%)
helped:                                   341
HURT:                                     0
GAINED:                                   2
LOST:                                     0
---
 .../drivers/dri/i965/brw_fs_copy_propagation.cpp   | 33 +++++++++++++++++++---
 1 file changed, 29 insertions(+), 4 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 e8d092c..d321509 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
@@ -275,6 +275,16 @@ is_logic_op(enum opcode opcode)
            opcode == BRW_OPCODE_NOT);
 }
 
+static bool
+can_change_source_types(fs_inst *inst)
+{
+   return !inst->src[0].abs && !inst->src[0].negate &&
+          (inst->opcode == BRW_OPCODE_MOV ||
+           (inst->opcode == BRW_OPCODE_SEL &&
+            inst->conditional_mod == BRW_CONDITIONAL_NONE &&
+            !inst->src[1].abs && !inst->src[1].negate));
+}
+
 bool
 fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
 {
@@ -346,7 +356,9 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
         type_sz(inst->src[arg].type)) % type_sz(entry->src.type) != 0)
       return false;
 
-   if (has_source_modifiers && entry->dst.type != inst->src[arg].type)
+   if (has_source_modifiers &&
+       entry->dst.type != inst->src[arg].type &&
+       !can_change_source_types(inst))
       return false;
 
    if (brw->gen >= 8 && (entry->src.negate || entry->src.abs) &&
@@ -412,9 +424,22 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
       break;
    }
 
-   if (!inst->src[arg].abs) {
-      inst->src[arg].abs = entry->src.abs;
-      inst->src[arg].negate ^= entry->src.negate;
+   if (has_source_modifiers) {
+      if (entry->dst.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 < inst->sources; i++)
+            inst->src[i].type = entry->dst.type;
+         inst->dst.type = entry->dst.type;
+      }
+
+      if (!inst->src[arg].abs) {
+         inst->src[arg].abs = entry->src.abs;
+         inst->src[arg].negate ^= entry->src.negate;
+      }
    }
 
    return true;
-- 
2.3.4