[MLIR] Add an option to disable maxIterations in greedy pattern rewrites

This option is needed for passes that are known to reach a fix point, but may
need many iterations depending on the size of the input IR.

Differential Revision: https://reviews.llvm.org/D111058

Author: frgossen

mlir/include/mlir/Transforms/GreedyPatternRewriteDriver.h

@@ -33,8 +33,11 @@ class GreedyRewriteConfig {
   bool enableRegionSimplification = true;
 
   /// This specifies the maximum number of times the rewriter will iterate
-  /// between applying patterns and simplifying regions.
-  unsigned maxIterations = 10;
+  /// between applying patterns and simplifying regions. Use `kNoIterationLimit`
+  /// to disable this iteration limit.
+  int64_t maxIterations = 10;
+
+  static constexpr int64_t kNoIterationLimit = -1;
 };
 
 //===----------------------------------------------------------------------===//

mlir/include/mlir/Transforms/Passes.td

@@ -378,7 +378,7 @@ def Canonicalizer : Pass<"canonicalize"> {
     Option<"enableRegionSimplification", "region-simplify", "bool",
            /*default=*/"true",
            "Seed the worklist in general top-down order">,
-    Option<"maxIterations", "max-iterations", "unsigned",
+    Option<"maxIterations", "max-iterations", "int64_t",
            /*default=*/"10",
            "Seed the worklist in general top-down order">
   ] # RewritePassUtils.options;

mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp

@@ -222,7 +222,9 @@ bool GreedyPatternRewriteDriver::simplify(MutableArrayRef<Region> regions) {
     // is kept up to date.
     if (config.enableRegionSimplification)
       changed |= succeeded(simplifyRegions(*this, regions));
-  } while (changed && ++iteration < config.maxIterations);
+  } while (changed &&
+           (++iteration < config.maxIterations ||
+            config.maxIterations == GreedyRewriteConfig::kNoIterationLimit));
 
   // Whether the rewrite converges, i.e. wasn't changed in the last iteration.
   return !changed;
@@ -345,7 +347,9 @@ LogicalResult OpPatternRewriteDriver::simplifyLocally(Operation *op,
     changed |= succeeded(matcher.matchAndRewrite(op, *this));
     if ((erased = opErasedViaPatternRewrites))
       return success();
-  } while (changed && ++iterations < maxIterations);
+  } while (changed &&
+           (++iterations < maxIterations ||
+            maxIterations == GreedyRewriteConfig::kNoIterationLimit));
 
   // Whether the rewrite converges, i.e. wasn't changed in the last iteration.
   return failure(changed);