nak: Disallow isetp.x pre-Volta

Fixes: a33507d621 ("nak/sm50: Set the .x bit for isetp")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30402>

src/nouveau/compiler/nak/hw_tests.rs

@@ -711,6 +711,10 @@ fn test_op_isetp() {
 
         let ex = i != 0;
 
+        if ex && RunSingleton::get().sm.sm() < 70 {
+            continue;
+        }
+
         let op = OpISetP {
             dst: Dst::None,
             set_op,

src/nouveau/compiler/nak/ir.rs

@@ -3699,32 +3699,18 @@ impl Foldable for OpISetP {
             }
         };
 
-        let dst = if sm.sm() >= 70 {
+        let cmp = if self.ex && x == y {
-            let cmp = if self.ex && x == y { low_cmp } else { cmp };
+            // Pre-Volta, isetp.x takes the accumulator into account.  If we
-            self.set_op.eval(cmp, accum)
+            // want to support this, we need to take an an accumulator into
+            // account.  Disallow it for now.
+            assert!(sm.sm() >= 70);
+            low_cmp
         } else {
-            if self.ex && x == y {
+            cmp
-                match self.cmp_op {
-                    IntCmpOp::Eq | IntCmpOp::Gt | IntCmpOp::Ge => {
-                        match &self.set_op {
-                            PredSetOp::And => false,
-                            PredSetOp::Or => accum,
-                            PredSetOp::Xor => accum,
-                        }
-                    }
-                    IntCmpOp::Ne | IntCmpOp::Lt | IntCmpOp::Le => {
-                        match &self.set_op {
-                            PredSetOp::And => accum,
-                            PredSetOp::Or => true,
-                            PredSetOp::Xor => !accum,
-                        }
-                    }
-                }
-            } else {
-                self.set_op.eval(cmp, accum)
-            }
         };
 
+        let dst = self.set_op.eval(cmp, accum);
+
         f.set_pred_dst(self, &self.dst, dst);
     }
 }

src/nouveau/compiler/nak/sm50.rs

@@ -1437,6 +1437,9 @@ impl SM50Op for OpISetP {
         e.set_reg_src(8..16, self.srcs[0]);
         e.set_pred_src(39..42, 42, self.accum);
 
+        // isetp.x seems to take the accumulator into account and we don't fully
+        // understand how.  Until we do, disallow it.
+        assert!(!self.ex);
         e.set_bit(43, self.ex);
         e.set_pred_set_op(45..47, self.set_op);