Address review comments.

This partially incorporates llvm#89552. I haven't exposed it on
canonicalizer pass as that could be distinct discussion.

Author: jpienaar

mlir/include/mlir/Transforms/GreedyPatternRewriteDriver.h

@@ -92,14 +92,13 @@ class GreedyRewriteConfig {
   /// An optional listener that should be notified about IR modifications.
   RewriterBase::Listener *listener = nullptr;
 
-  // Whether this should fold while greedily rewriting.
-  //
-  // Note: greedy here generally refers to two forms, 1) greedily applying
-  // patterns based purely on benefit and applying without backtracking using
-  // default cost model, 2) greedily folding where possible while attempting to
-  // match and rewrite using the provided patterns. With this option set to
-  // false it only does the former.
+  /// Whether this should fold while greedily rewriting. This also disables
+  /// CSE'ing constants.
   bool fold = true;
+
+  /// If set to "true", constants are CSE'd (even across multiple regions that
+  /// are in a parent-ancestor relationship).
+  bool cseConstants = true;
 };
 
 //===----------------------------------------------------------------------===//

mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp

@@ -840,11 +840,6 @@ LogicalResult RegionPatternRewriteDriver::simplify(bool *changed) && {
     // regions to enable more aggressive CSE'ing).
     OperationFolder folder(ctx, this);
     auto insertKnownConstant = [&](Operation *op) {
-      // This hoisting is to enable more folding, so skip checking if known
-      // constant, updating dense map etc if not doing folding.
-      if (!config.fold)
-        return false;
-
       // Check for existing constants when populating the worklist. This avoids
       // accidentally reversing the constant order during processing.
       Attribute constValue;
@@ -857,13 +852,13 @@ LogicalResult RegionPatternRewriteDriver::simplify(bool *changed) && {
     if (!config.useTopDownTraversal) {
       // Add operations to the worklist in postorder.
       region.walk([&](Operation *op) {
-        if (!insertKnownConstant(op))
+        if (!config.cseConstants || !insertKnownConstant(op))
           addToWorklist(op);
       });
     } else {
       // Add all nested operations to the worklist in preorder.
       region.walk<WalkOrder::PreOrder>([&](Operation *op) {
-        if (!insertKnownConstant(op)) {
+        if (!config.cseConstants || !insertKnownConstant(op)) {
           addToWorklist(op);
           return WalkResult::advance();
         }