[Mesa-dev] [PATCH] i965/fs: Reset the register file to VGRF in lower_integer_multiplication

[Jason Ekstrand]

18fde36ced4279f2577097a1a7d31b55f2f5f141 changed the way temporary
registers were allocated in lower_integer_multiplication so that we
allocate regs_written(inst) space and keep the stride of the original
destination register.  This was to ensure that any MUL which originally
followed the CHV/BXT integer multiply regioning restrictions would
continue to follow those restrictions even after lowering.  This works
fine except that I forgot to reset the register file to VGRF so, even
though they were assigned a number from alloc.allocate(), they had the
wrong register file.  This caused some GLES 3.0 CTS tests to start
failing on Sandy Bridge due to attempted reads from the MRF:

    ES3-CTS.functional.shaders.precision.int.highp_mul_fragment.snbm64
    ES3-CTS.functional.shaders.precision.int.mediump_mul_fragment.snbm64
    ES3-CTS.functional.shaders.precision.int.lowp_mul_fragment.snbm64
    ES3-CTS.functional.shaders.precision.uint.highp_mul_fragment.snbm64
    ES3-CTS.functional.shaders.precision.uint.mediump_mul_fragment.snbm64
    ES3-CTS.functional.shaders.precision.uint.lowp_mul_fragment.snbm64

This commit remedies this problem by, instead of copying inst->dst and
overwriting nr, just make a new register and set the region to match
inst->dst.

Cc: Matt Turner <mattst88 at gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103626
Fixes: 18fde36ced4279f2577097a1a7d31b55f2f5f141
Cc: "17.3" <mesa-stable at lists.freedesktop.org>
---
 src/intel/compiler/brw_fs.cpp | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp
index 3717c50..db5468c 100644
--- a/src/intel/compiler/brw_fs.cpp
+++ b/src/intel/compiler/brw_fs.cpp
@@ -3631,13 +3631,18 @@ fs_visitor::lower_integer_multiplication()
                 regions_overlap(inst->dst, inst->size_written,
                                 inst->src[1], inst->size_read(1))) {
                needs_mov = true;
-               low.nr = alloc.allocate(regs_written(inst));
-               low.offset = low.offset % REG_SIZE;
+               /* Get a new VGRF but keep the same stride as inst->dst */
+               low = fs_reg(VGRF, alloc.allocate(regs_written(inst)),
+                            inst->dst.type);
+               low.stride = inst->dst.stride;
+               low.offset = inst->dst.offset % REG_SIZE;
             }
 
-            fs_reg high = inst->dst;
-            high.nr = alloc.allocate(regs_written(inst));
-            high.offset = high.offset % REG_SIZE;
+            /* Get a new VGRF but keep the same stride as inst->dst */
+            fs_reg high(VGRF, alloc.allocate(regs_written(inst)),
+                        inst->dst.type);
+            high.stride = inst->dst.stride;
+            high.offset = inst->dst.offset % REG_SIZE;
 
             if (devinfo->gen >= 7) {
                if (inst->src[1].file == IMM) {
-- 
2.5.0.400.gff86faf