fix: prevent canonicalize looping for extremely long time

include/circt/Reduce/GenericReductions.h

@@ -10,13 +10,19 @@
 #define CIRCT_REDUCE_GENERICREDUCTIONS_H
 
 #include "circt/Reduce/Reduction.h"
+#include <optional>
 
 namespace circt {
 
 /// Populate reduction patterns that are not specific to certain operations or
-/// dialects
-void populateGenericReducePatterns(MLIRContext *context,
-                                   ReducePatternSet &patterns);
+/// dialects.
+///
+/// The optional `maxNumRewrites` parameter allows callers to override the
+/// greedy rewrite budget used by reductions that rely on the canonicalizer
+/// pass.
+void populateGenericReducePatterns(
+    MLIRContext *context, ReducePatternSet &patterns,
+    std::optional<int64_t> maxNumRewrites = std::nullopt);
 
 } // namespace circt
 

lib/Reduce/GenericReductions.cpp

@@ -96,18 +96,23 @@ struct MakeSymbolsPrivate : public Reduction {
 // Reduction Registration
 //===----------------------------------------------------------------------===//
 
-static std::unique_ptr<Pass> createSimpleCanonicalizerPass() {
+static std::unique_ptr<Pass>
+createSimpleCanonicalizerPass(std::optional<int64_t> maxNumRewrites) {
   GreedyRewriteConfig config;
   config.setUseTopDownTraversal(true);
   config.setRegionSimplificationLevel(
       mlir::GreedySimplifyRegionLevel::Disabled);
+  if (maxNumRewrites)
+    config.setMaxNumRewrites(*maxNumRewrites);
   return createCanonicalizerPass(config);
 }
 
-void circt::populateGenericReducePatterns(MLIRContext *context,
-                                          ReducePatternSet &patterns) {
+void circt::populateGenericReducePatterns(
+    MLIRContext *context, ReducePatternSet &patterns,
+    std::optional<int64_t> maxNumRewrites) {
   patterns.add<PassReduction, 103>(context, createSymbolDCEPass());
-  patterns.add<PassReduction, 102>(context, createSimpleCanonicalizerPass());
+  patterns.add<PassReduction, 102>(
+      context, createSimpleCanonicalizerPass(maxNumRewrites));
   patterns.add<PassReduction, 101>(context, createCSEPass());
   patterns.add<MakeSymbolsPrivate, 100>();
   patterns.add<UnusedSymbolPruner, 99>();

tools/circt-reduce/circt-reduce.cpp

@@ -104,6 +104,12 @@ static cl::opt<bool> verbose("v", cl::init(true),
                              cl::desc("Print reduction progress to stderr"),
                              cl::cat(mainCategory));
 
+cl::opt<int64_t> maxNumRewrites(
+    "max-num-rewrites", cl::init(-1),
+    cl::desc("Maximum number of rewrites GreedyPatternRewriteDriver may "
+             "apply (negative value keeps the default)"),
+    cl::cat(mainCategory));
+
 static cl::opt<unsigned>
     maxChunks("max-chunks", cl::init(0),
               cl::desc("Stop increasing granularity beyond this number of "
@@ -193,7 +199,10 @@ static LogicalResult execute(MLIRContext &context) {
 
   // Gather a list of reduction patterns that we should try.
   ReducePatternSet patterns;
-  populateGenericReducePatterns(&context, patterns);
+  std::optional<int64_t> maxNumRewritesOpt;
+  if (maxNumRewrites >= 0)
+    maxNumRewritesOpt = maxNumRewrites;
+  populateGenericReducePatterns(&context, patterns, maxNumRewritesOpt);
   ReducePatternInterfaceCollection reducePatternCollection(&context);
   reducePatternCollection.populateReducePatterns(patterns);
   auto reductionFilter = [&](const Reduction &reduction) {