[Mesa-dev] [PATCH 1/2] i965/fs: Force promotion of src0 immediates.

[Kenneth Graunke]

Commit 36bc5f06dd22 began allowing immediates in MAD and LRP sources,
in any position.  One unforeseen consequence is that opt_algebraic began
creating ADD and MUL instructions with src0 immediates.

For example,

   mad(8) vgrf86:F, 1.000000f, 1.000000f, vgrf84:F

would be optimized into:

   add(8) vgrf86:F, 1.000000f, vgrf84:F

which is illegal.

Fixes assert failures in steam/tiny-and-big-grandpas-leftovers/fp-19.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_fs_combine_constants.cpp | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Last night I was importing new shaders into shader-db, and came across
a shader that hit an assertion.  I started looking into it this morning,
and wrote these patches...before I caught up on mesa-dev and realized
that Tapani was also working on this.  Sorry for the collision!

I think this might be a more general solution, and should allow us to
propagate immediates into src0 on all instructions, if we want to.

diff --git a/src/mesa/drivers/dri/i965/brw_fs_combine_constants.cpp b/src/mesa/drivers/dri/i965/brw_fs_combine_constants.cpp
index 7ddb253..a3657e0 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_combine_constants.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_combine_constants.cpp
@@ -207,7 +207,8 @@ fs_visitor::opt_combine_constants()
    foreach_block_and_inst(block, fs_inst, inst, cfg) {
       ip++;
 
-      if (!could_coissue(brw, inst) && !must_promote_imm(inst))
+      if (!could_coissue(brw, inst) && !must_promote_imm(inst) &&
+          !(inst->sources > 1 && inst->src[0].file == IMM))
          continue;
 
       for (int i = 0; i < inst->sources; i++) {
@@ -225,7 +226,8 @@ fs_visitor::opt_combine_constants()
             imm->block = intersection;
             imm->uses->push_tail(link(const_ctx, &inst->src[i]));
             imm->uses_by_coissue += could_coissue(brw, inst);
-            imm->must_promote = imm->must_promote || must_promote_imm(inst);
+            imm->must_promote = imm->must_promote ||
+               must_promote_imm(inst) || (i == 0 && inst->sources > 1);
             imm->last_use_ip = ip;
          } else {
             imm = new_imm(&table, const_ctx);
@@ -235,7 +237,8 @@ fs_visitor::opt_combine_constants()
             imm->uses->push_tail(link(const_ctx, &inst->src[i]));
             imm->val = val;
             imm->uses_by_coissue = could_coissue(brw, inst);
-            imm->must_promote = must_promote_imm(inst);
+            imm->must_promote =
+               must_promote_imm(inst) || (i == 0 && inst->sources > 1);
             imm->first_use_ip = ip;
             imm->last_use_ip = ip;
          }
-- 
2.2.2