nak: Implement discard and demote

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24998>

src/nouveau/compiler/nak_encode_sm75.rs

@@ -1536,6 +1536,11 @@ impl SM75Instr {
         self.set_field(72..80, op.idx);
     }
 
+    fn encode_kill(&mut self, op: &OpKill) {
+        self.set_opcode(0x95b);
+        self.set_pred_src(87..90, 90, SrcRef::True.into());
+    }
+
     fn encode_pixld(&mut self, op: &OpPixLd) {
         self.set_opcode(0x925);
         self.set_dst(op.dst);
@@ -1621,6 +1626,7 @@ impl SM75Instr {
             Op::Exit(op) => si.encode_exit(&op),
             Op::Bar(op) => si.encode_bar(&op),
             Op::CS2R(op) => si.encode_cs2r(&op),
+            Op::Kill(op) => si.encode_kill(&op),
             Op::PixLd(op) => si.encode_pixld(&op),
             Op::S2R(op) => si.encode_s2r(&op),
             _ => panic!("Unhandled instruction"),

src/nouveau/compiler/nak_from_nir.rs

@@ -1110,6 +1110,13 @@ impl<'a> ShaderFromNir<'a> {
                     data: data,
                 });
             }
+            nir_intrinsic_demote | nir_intrinsic_discard => {
+                b.push_op(OpKill {});
+            }
+            nir_intrinsic_demote_if | nir_intrinsic_discard_if => {
+                let cond = self.get_ssa(&srcs[0].as_def())[0];
+                b.predicate(cond.into()).push_op(OpKill {});
+            }
             nir_intrinsic_global_atomic => {
                 let bit_size = intrin.def.bit_size();
                 let (addr, offset) = self.get_io_addr_offset(&srcs[0], 24);

src/nouveau/compiler/nak_ir.rs

@@ -3277,6 +3277,16 @@ impl fmt::Display for OpCS2R {
     }
 }
 
+#[repr(C)]
+#[derive(SrcsAsSlice, DstsAsSlice)]
+pub struct OpKill {}
+
+impl fmt::Display for OpKill {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "KILL")
+    }
+}
+
 pub enum PixVal {
     MsCount,
     CovMask,
@@ -3685,6 +3695,7 @@ pub enum Op {
     Exit(OpExit),
     Bar(OpBar),
     CS2R(OpCS2R),
+    Kill(OpKill),
     PixLd(OpPixLd),
     S2R(OpS2R),
     Undef(OpUndef),
@@ -4002,6 +4013,7 @@ impl Instr {
             | Op::Atom(_)
             | Op::AtomCas(_)
             | Op::MemBar(_)
+            | Op::Kill(_)
             | Op::Bra(_)
             | Op::Exit(_)
             | Op::Bar(_)
@@ -4074,7 +4086,11 @@ impl Instr {
             Op::Bra(_) | Op::Exit(_) => true,
 
             // Miscellaneous ops
-            Op::Bar(_) | Op::CS2R(_) | Op::PixLd(_) | Op::S2R(_) => false,
+            Op::Bar(_)
+            | Op::CS2R(_)
+            | Op::Kill(_)
+            | Op::PixLd(_)
+            | Op::S2R(_) => false,
 
             // Virtual ops
             Op::Undef(_)