nak: Put the cycle count assert behind a debug flag

Fixes: c1d64053f2 ("nak: Assert instr_sched matches calc_instr_deps")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33573>

src/nouveau/compiler/nak/api.rs

@@ -25,6 +25,7 @@ enum DebugFlags {
     Spill,
     Annotate,
     NoUgpr,
+    Cycles,
 }
 
 pub struct Debug {
@@ -49,6 +50,7 @@ impl Debug {
                 "spill" => flags |= 1 << DebugFlags::Spill as u8,
                 "annotate" => flags |= 1 << DebugFlags::Annotate as u8,
                 "nougpr" => flags |= 1 << DebugFlags::NoUgpr as u8,
+                "cycles" => flags |= 1 << DebugFlags::Cycles as u8,
                 unk => eprintln!("Unknown NAK_DEBUG flag \"{}\"", unk),
             }
         }
@@ -78,6 +80,10 @@ pub trait GetDebugFlags {
     fn no_ugpr(&self) -> bool {
         self.debug_flags() & (1 << DebugFlags::NoUgpr as u8) != 0
     }
+
+    fn cycles(&self) -> bool {
+        self.debug_flags() & (1 << DebugFlags::Cycles as u8) != 0
+    }
 }
 
 pub static DEBUG: OnceLock<Debug> = OnceLock::new();

src/nouveau/compiler/nak/calc_instr_deps.rs

@@ -512,11 +512,16 @@ impl Shader<'_> {
                 min_num_static_cycles += calc_delays(f, self.sm);
             }
 
-            // Check that this file's model matches up with the model in
-            // opt_instr_sched_postpass. postpass includes an estimate of
-            // variable latency delays in its count, so we expect it to be >=
-            // the estimate here
-            assert!(self.info.num_static_cycles >= min_num_static_cycles);
+            if DEBUG.cycles() {
+                // This is useful for debugging differences in the scheduler
+                // cycle count model and the calc_delays() model.  However, it
+                // isn't totally valid since assign_barriers() can add extra
+                // dependencies for barrier re-use and those may add cycles.
+                // The chances of it doing this are low, thanks to our LRU
+                // allocation strategy, but it's still not an assert we want
+                // running in production.
+                assert!(self.info.num_static_cycles >= min_num_static_cycles);
+            }
         }
     }
 }