intel/fs/bank_conflicts: Don't touch Gen7 MRF hack registers.

Fixes: af2c320190 "intel/fs: Implement GRF bank conflict mitigation pass."
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104199
Reported-by: Darius Spitznagel <d.spitznagel@goodbytez.de>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/intel/compiler/brw_fs.cpp

@@ -945,7 +945,7 @@ fs_inst::flags_written() const
  * instruction -- the FS opcodes often generate MOVs in addition.
  */
 int
-fs_visitor::implied_mrf_writes(fs_inst *inst)
+fs_visitor::implied_mrf_writes(fs_inst *inst) const
 {
    if (inst->mlen == 0)
       return 0;

src/intel/compiler/brw_fs.h

@@ -277,7 +277,7 @@ public:
 
    struct brw_reg interp_reg(int location, int channel);
 
-   int implied_mrf_writes(fs_inst *inst);
+   int implied_mrf_writes(fs_inst *inst) const;
 
    virtual void dump_instructions();
    virtual void dump_instructions(const char *name);

src/intel/compiler/brw_fs_bank_conflicts.cpp

@@ -530,12 +530,12 @@ namespace {
       for (unsigned reg = 0; reg < 2; reg++)
          constrained[p.atom_of_reg(reg)] = true;
 
+      foreach_block_and_inst(block, fs_inst, inst, v->cfg) {
          /* Assume that anything referenced via fixed GRFs is baked into the
           * hardware's fixed-function logic and may be unsafe to move around.
           * Also take into account the source GRF restrictions of EOT
           * send-message instructions.
           */
-      foreach_block_and_inst(block, fs_inst, inst, v->cfg) {
          if (inst->dst.file == FIXED_GRF)
             constrained[p.atom_of_reg(reg_of(inst->dst))] = true;
 
@@ -544,6 +544,18 @@ namespace {
                 (is_grf(inst->src[i]) && inst->eot))
                constrained[p.atom_of_reg(reg_of(inst->src[i]))] = 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.
+          */
+         if (v->devinfo->gen >= 7) {
+            assert(inst->dst.file != MRF);
+
+            for (int i = 0; i < v->implied_mrf_writes(inst); i++) {
+               const unsigned reg = GEN7_MRF_HACK_START + inst->base_mrf + i;
+               constrained[p.atom_of_reg(reg)] = true;
+            }
+         }
       }
 
       return constrained;