intel/compiler: Don't cmod propagate into a saturated operation

Shader-db results on Sky Lake:

    total instructions in shared programs: 12954445 -> 12955125 (0.01%)
    instructions in affected programs: 141862 -> 142542 (0.48%)
    helped: 0
    HURT: 626

Reviewed-by: Matt Turner <[email protected]>
Cc: [email protected]

2 files changed, 16 insertions, 0 deletions

diff --git a/src/intel/compiler/brw_fs_cmod_propagation.cpp b/src/intel/compiler/brw_fs_cmod_propagation.cpp
index 2d50c92e9e3..db63e942b75 100644
--- a/src/intel/compiler/brw_fs_cmod_propagation.cpp
+++ b/src/intel/compiler/brw_fs_cmod_propagation.cpp
@@ -142,6 +142,14 @@ opt_cmod_propagation_local(const gen_device_info *devinfo, bblock_t *block)
                 scan_inst->opcode == BRW_OPCODE_CMPN)
                break;
 
+            /* From the Sky Lake PRM Vol. 7 "Assigning Conditional Mods":
+             *
+             *    * Note that the [post condition signal] bits generated at
+             *      the output of a compute are before the .sat.
+             */
+            if (scan_inst->saturate)
+               break;
+
             /* Otherwise, try propagating the conditional. */
             enum brw_conditional_mod cond =
                inst->src[0].negate ? brw_swap_cmod(inst->conditional_mod)
diff --git a/src/intel/compiler/brw_vec4_cmod_propagation.cpp b/src/intel/compiler/brw_vec4_cmod_propagation.cpp
index 4454cdbfc94..05e65168193 100644
--- a/src/intel/compiler/brw_vec4_cmod_propagation.cpp
+++ b/src/intel/compiler/brw_vec4_cmod_propagation.cpp
@@ -129,6 +129,14 @@ opt_cmod_propagation_local(bblock_t *block)
                 scan_inst->opcode == BRW_OPCODE_CMPN)
                break;
 
+            /* From the Sky Lake PRM Vol. 7 "Assigning Conditional Mods":
+             *
+             *    * Note that the [post condition signal] bits generated at
+             *      the output of a compute are before the .sat.
+             */
+            if (scan_inst->saturate)
+               break;
+
             /* Otherwise, try propagating the conditional. */
             enum brw_conditional_mod cond =
                inst->src[0].negate ? brw_swap_cmod(inst->conditional_mod)