Mesa (master): aco: fix waiting for scalar stores before "writing back" data on GFX8-GFX9

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Module: Mesa
Branch: master
Commit: 34fd894e42ae1ec9d35bf9c4f05364b03dd4a223
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=34fd894e42ae1ec9d35bf9c4f05364b03dd4a223

Author: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Date:   Fri Feb  7 16:33:35 2020 +0100

aco: fix waiting for scalar stores before "writing back" data on GFX8-GFX9

Seems required also on GFX8-GFX9 to achieve correct behaviour. This
is an undocumented behaviour but it makes real sense to me.

pipeline-db on GFX9:
Totals from affected shaders:
SGPRS: 1018 -> 1018 (0.00 %)
VGPRS: 516 -> 516 (0.00 %)
Code Size: 40516 -> 40636 (0.30 %) bytes
Max Waves: 280 -> 280 (0.00 %)

This fixes some sort of sun flickering with Assassins Creed Origins.

Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2488
Cc: <mesa-stable at lists.freedesktop.org>
Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Reviewed-by: Daniel Schürmann <daniel at schuermann.dev>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3750>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3750>

---

 src/amd/compiler/aco_insert_waitcnt.cpp | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/amd/compiler/aco_insert_waitcnt.cpp b/src/amd/compiler/aco_insert_waitcnt.cpp
index 5ec9636752d..8d8024f5aa2 100644
--- a/src/amd/compiler/aco_insert_waitcnt.cpp
+++ b/src/amd/compiler/aco_insert_waitcnt.cpp
@@ -374,13 +374,16 @@ wait_imm kill(Instruction* instr, wait_ctx& ctx)
 
    imm.combine(parse_wait_instr(ctx, instr));
 
-   if (ctx.chip_class >= GFX10) {
-      /* Seems to be required on GFX10 to achieve correct behaviour.
-       * It shouldn't cost anything anyways since we're about to do s_endpgm.
-       */
-      if (ctx.lgkm_cnt && instr->opcode == aco_opcode::s_dcache_wb)
-         imm.lgkm = 0;
 
+   /* It's required to wait for scalar stores before "writing back" data.
+    * It shouldn't cost anything anyways since we're about to do s_endpgm.
+    */
+   if (ctx.lgkm_cnt && instr->opcode == aco_opcode::s_dcache_wb) {
+      assert(ctx.chip_class >= GFX8);
+      imm.lgkm = 0;
+   }
+
+   if (ctx.chip_class >= GFX10) {
       /* GFX10: A store followed by a load at the same address causes a problem because
        * the load doesn't load the correct values unless we wait for the store first.
        * This is NOT mitigated by an s_nop.