intel/compiler: Don't propagate cmod into integer multiplies

No shader-db change on Sky Lake.

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

1 files changed, 17 insertions, 0 deletions

diff --git a/src/intel/compiler/brw_fs_cmod_propagation.cpp b/src/intel/compiler/brw_fs_cmod_propagation.cpp
index db63e942b75..4625d69f89e 100644
--- a/src/intel/compiler/brw_fs_cmod_propagation.cpp
+++ b/src/intel/compiler/brw_fs_cmod_propagation.cpp
@@ -150,6 +150,23 @@ opt_cmod_propagation_local(const gen_device_info *devinfo, bblock_t *block)
             if (scan_inst->saturate)
                break;
 
+            /* From the Sky Lake PRM, Vol 2a, "Multiply":
+             *
+             *    "When multiplying integer data types, if one of the sources
+             *     is a DW, the resulting full precision data is stored in
+             *     the accumulator. However, if the destination data type is
+             *     either W or DW, the low bits of the result are written to
+             *     the destination register and the remaining high bits are
+             *     discarded. This results in undefined Overflow and Sign
+             *     flags. Therefore, conditional modifiers and saturation
+             *     (.sat) cannot be used in this case."
+             *
+             * We just disallow cmod propagation on all integer multiplies.
+             */
+            if (!brw_reg_type_is_floating_point(scan_inst->dst.type) &&
+                scan_inst->opcode == BRW_OPCODE_MUL)
+               break;
+
             /* Otherwise, try propagating the conditional. */
             enum brw_conditional_mod cond =
                inst->src[0].negate ? brw_swap_cmod(inst->conditional_mod)