Mesa (master): aco: try to better align 8+ dword SGPR vectors

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Module: Mesa
Branch: master
Commit: f8c7661ecaa782fdde105a4bf756023eb88ea780
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=f8c7661ecaa782fdde105a4bf756023eb88ea780

Author: Rhys Perry <pendingchaos02 at gmail.com>
Date:   Tue Aug 25 19:10:52 2020 +0100

aco: try to better align 8+ dword SGPR vectors

This doesn't have much of an effect, but it helps avoid a
pathological case for Assassin's Creed Valhalla and a RDR2 shader with a
future change.

fossil-db (Sienna):
Totals from 55074 (39.51% of 139391) affected shaders:
SGPRs: 3515076 -> 3567744 (+1.50%); split: -0.01%, +1.51%
CodeSize: 206942120 -> 206941868 (-0.00%); split: -0.00%, +0.00%
Instrs: 39625900 -> 39625837 (-0.00%); split: -0.00%, +0.00%
Cycles: 1640088780 -> 1640088828 (+0.00%); split: -0.00%, +0.00%

Signed-off-by: Rhys Perry <pendingchaos02 at gmail.com>
Reviewed-by: Daniel Schürmann <daniel at schuermann.dev>
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/4070
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8416>

---

 src/amd/compiler/aco_register_allocation.cpp | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/src/amd/compiler/aco_register_allocation.cpp b/src/amd/compiler/aco_register_allocation.cpp
index 3f0f44b6bf6..2fadcef4a72 100644
--- a/src/amd/compiler/aco_register_allocation.cpp
+++ b/src/amd/compiler/aco_register_allocation.cpp
@@ -632,16 +632,18 @@ std::pair<PhysReg, bool> get_reg_simple(ra_ctx& ctx,
    uint32_t stride = info.rc.is_subdword() ? DIV_ROUND_UP(info.stride, 4) : info.stride;
    RegClass rc = info.rc;
 
+   DefInfo new_info = info;
+   for (unsigned new_stride = 16; new_stride > stride; new_stride /= 2) {
+      if (size % new_stride)
+         continue;
+      new_info.stride = new_stride;
+      std::pair<PhysReg, bool> res = get_reg_simple(ctx, reg_file, new_info);
+      if (res.second)
+         return res;
+   }
+
    if (stride == 1) {
       info.rc = RegClass(rc.type(), size);
-      for (unsigned new_stride = 8; new_stride > 1; new_stride /= 2) {
-         if (size % new_stride)
-            continue;
-         info.stride = new_stride;
-         std::pair<PhysReg, bool> res = get_reg_simple(ctx, reg_file, info);
-         if (res.second)
-            return res;
-      }
 
       /* best fit algorithm: find the smallest gap to fit in the variable */
       unsigned best_pos = 0xFFFF;