[xls][mlir] Sort spawns regions topologically after OptimizeSpawns fi…

…nishes

We apply patterns that modify two regions, the next and spawns regions. The edits
to the next region always obey dominance rules, but the changes to the spawns regions
are not guaranteed to (we don't have a perfect place to insert our new spawn instruction).

Rather than trying to guarantee it which may be hard, simply sort the spawns regions after
the optimization runs.

PiperOrigin-RevId: 701078946

xls/contrib/mlir/BUILD

@@ -483,6 +483,7 @@ cc_library(
     deps = [
         ":mlir_xls",
         ":xls_transforms_passes_inc_gen",
+        "@llvm-project//mlir:Analysis",
         "@llvm-project//mlir:FuncDialect",
         "@llvm-project//mlir:IR",
         "@llvm-project//mlir:Pass",

xls/contrib/mlir/transforms/optimize_spawns.cc

@@ -16,6 +16,7 @@
 #include <cstdint>
 #include <utility>
 
+#include "mlir/include/mlir/Analysis/TopologicalSortUtils.h"
 #include "mlir/include/mlir/Dialect/Func/IR/FuncOps.h"
 #include "mlir/include/mlir/IR/PatternMatch.h"
 #include "mlir/include/mlir/IR/Value.h"
@@ -115,6 +116,10 @@ class OptimizeSpawnsPass
                                             std::move(patterns)))) {
       signalPassFailure();
     }
+
+    // Ensure that all spawns regions are topologically sorted; given the order
+    // in which the pattern is applied, this is not currently guaranteed.
+    sortTopologically(&getOperation().getSpawns().front());
   }
 };