Mesa (master): intel/fs/gen6: Constrain barycentric source of LINTERP during bank conflict mitigation.

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Module: Mesa
Branch: master
Commit: 0db4455c1f2f3cff76f3c15081c020c0fb229a47
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=0db4455c1f2f3cff76f3c15081c020c0fb229a47

Author: Francisco Jerez <currojerez at riseup.net>
Date:   Mon Dec 30 16:34:22 2019 -0800

intel/fs/gen6: Constrain barycentric source of LINTERP during bank conflict mitigation.

This avoids regressions on SNB due to the bank conflict mitigation
pass moving a VGRF-allocated barycentric vector to a misaligned
location, which would prevent the PLN instruction from being used.

Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

---

 src/intel/compiler/brw_fs_bank_conflicts.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/intel/compiler/brw_fs_bank_conflicts.cpp b/src/intel/compiler/brw_fs_bank_conflicts.cpp
index e908d0e38fc..f10caf249d0 100644
--- a/src/intel/compiler/brw_fs_bank_conflicts.cpp
+++ b/src/intel/compiler/brw_fs_bank_conflicts.cpp
@@ -567,6 +567,14 @@ namespace {
                constrained[p.atom_of_reg(reg_of(inst->src[i]))] = true;
          }
 
+         /* Preserve the original allocation of VGRFs used by the barycentric
+          * source of the LINTERP instruction on Gen6, since pair-aligned
+          * barycentrics allow the PLN instruction to be used.
+          */
+         if (v->devinfo->has_pln && v->devinfo->gen <= 6 &&
+             inst->opcode == FS_OPCODE_LINTERP)
+            constrained[p.atom_of_reg(reg_of(inst->src[0]))] = true;
+
          /* The location of the Gen7 MRF hack registers is hard-coded in the
           * rest of the compiler back-end.  Don't attempt to move them around.
           */