Module: Mesa
Branch: main
Commit: 8f8cde4c6050d1e91101ec66e8982036da9d7700
URL:
http://cgit.freedesktop.org/mesa/mesa/commit/?id=8f8cde4c6050d1e91101ec66e8982036da9d7700
Author: Sviatoslav Peleshko <sviatoslav.peles...@globallogic.com>
Date: Fri Oct 13 05:02:22 2023 +0300
intel/fs: Don't optimize DW*1 MUL if it stores value to the accumulator
Fixes: a8b86459 ("i965/fs: Optimize a * 1.0 -> a.")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/9570
Signed-off-by: Sviatoslav Peleshko <sviatoslav.peles...@globallogic.com>
Reviewed-by: Ian Romanick <ian.d.roman...@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25710>
---
src/intel/compiler/brw_fs.cpp | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp
index 9dd660a1a81..ce43e53f2d3 100644
--- a/src/intel/compiler/brw_fs.cpp
+++ b/src/intel/compiler/brw_fs.cpp
@@ -2444,6 +2444,29 @@ fs_visitor::opt_algebraic()
if (brw_reg_type_is_floating_point(inst->src[1].type))
break;
+ /* From the BDW PRM, Vol 2a, "mul - Multiply":
+ *
+ * "When multiplying integer datatypes, if src0 is DW and src1
+ * is W, irrespective of the destination datatype, the
+ * accumulator maintains full 48-bit precision."
+ * ...
+ * "When multiplying integer data types, if one of the sources
+ * is a DW, the resulting full precision data is stored in
+ * the accumulator."
+ *
+ * There are also similar notes in earlier PRMs.
+ *
+ * The MOV instruction can copy the bits of the source, but it
+ * does not clear the higher bits of the accumulator. So, because
+ * we might use the full accumulator in the MUL/MACH macro, we
+ * shouldn't replace such MULs with MOVs.
+ */
+ if ((brw_reg_type_to_size(inst->src[0].type) == 4 ||
+ brw_reg_type_to_size(inst->src[1].type) == 4) &&
+ (inst->dst.is_accumulator() ||
+ inst->writes_accumulator_implicitly(devinfo)))
+ break;
+
/* a * 1.0 = a */
if (inst->src[1].is_one()) {
inst->opcode = BRW_OPCODE_MOV;
