r600/sfn: try all possible configurations when splitting multi-slot instructions

With that we can better schedule these instructions into groups.

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36921>

src/gallium/drivers/r600/sfn/sfn_scheduler.cpp

@@ -956,8 +956,31 @@ BlockScheduler::schedule_alu_multislot_to_group_vec(AluGroup *group, ValueFactor
    auto e = alu_multi_slot_ready.end();
 
    while (i != e && util_bitcount(group->free_slot_mask()) > 1) {
-      auto required_mask = (*i)->required_channels_mask();
-      if ((group->free_slot_mask() & required_mask) != required_mask) {
+
+      auto dest = (*i)->dest();
+      assert(dest);
+
+      bool can_merge = false;
+      unsigned allowed_dest_chan_mask = (*i)->allowed_dest_chan_mask();
+      while (allowed_dest_chan_mask) {
+
+         auto required_mask = (*i)->required_channels_mask();
+
+         if ((group->free_slot_mask() & required_mask) == required_mask) {
+            can_merge = true;
+            break;
+         }
+
+         allowed_dest_chan_mask &= ~BITFIELD_BIT((*i)->dest_chan());
+         int new_chan = u_bit_scan(&allowed_dest_chan_mask);
+
+         if (!dest->can_switch_to_chan(new_chan))
+            break;
+
+         dest->set_chan(new_chan);
+      }
+
+      if (!can_merge) {
          ++i;
          continue;
       }

src/gallium/drivers/r600/sfn/sfn_virtualvalues.cpp

@@ -241,6 +241,27 @@ Register::accept(ConstRegisterVisitor& visitor) const
    visitor.visit(*this);
 }
 
+bool
+Register::can_switch_to_chan(int c)
+{
+   if (pin() != pin_free && pin() != pin_group)
+      return false;
+
+   int free_mask = BITSET_BIT(c);
+   for (auto p : parents()) {
+      auto alu = p->as_alu();
+      if (alu)
+         free_mask &= alu->allowed_dest_chan_mask();
+   }
+
+   for (auto u : uses()) {
+      free_mask &= u->allowed_src_chan_mask();
+      if (!free_mask)
+         return false;
+   }
+   return true;
+}
+
 void
 Register::print(std::ostream& os) const
 {

src/gallium/drivers/r600/sfn/sfn_virtualvalues.h

@@ -169,6 +169,8 @@ public:
    bool has_uses() const { return !m_uses.empty() || pin() == pin_array; }
    void set_chan(int c) { do_set_chan(c); }
 
+   bool can_switch_to_chan(int c);
+
    virtual VirtualValue *addr() const { return nullptr; }
 
    int index() const { return m_index; }