add max length mode for dumps (if using custom opt passes) (#1289)

* add max length mode for dumps (if using custom opt passes)

* Apply suggestions from code review

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: wsmoses

src/mlir/IR/Pass.jl

@@ -98,6 +98,9 @@ function dump_mlir(
         if isempty(mode)
             fname *= ".mlir"
         else
+            if length(mode) > 100
+                mode = mode[1:100]
+            end
             fname *= "_$(mode).mlir"
         end
         MLIR_DUMP_COUNTER[] += 1