1 files changed, 95 insertions, 1 deletions

diff --git a/mlir/lib/Dialect/SCF/IR/SCF.cpp b/mlir/lib/Dialect/SCF/IR/SCF.cpp
index 9bd13f3..744a595 100644
--- a/mlir/lib/Dialect/SCF/IR/SCF.cpp
+++ b/mlir/lib/Dialect/SCF/IR/SCF.cpp
@@ -27,6 +27,7 @@
 #include "mlir/Interfaces/ValueBoundsOpInterface.h"
 #include "mlir/Transforms/InliningUtils.h"
 #include "llvm/ADT/MapVector.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/DebugLog.h"
@@ -291,9 +292,102 @@ struct MultiBlockExecuteInliner : public OpRewritePattern<ExecuteRegionOp> {
   }
 };
 
+// Pattern to eliminate ExecuteRegionOp results which forward external
+// values from the region. In case there are multiple yield operations,
+// all of them must have the same operands in order for the pattern to be
+// applicable.
+struct ExecuteRegionForwardingEliminator
+    : public OpRewritePattern<ExecuteRegionOp> {
+  using OpRewritePattern<ExecuteRegionOp>::OpRewritePattern;
+
+  LogicalResult matchAndRewrite(ExecuteRegionOp op,
+                                PatternRewriter &rewriter) const override {
+    if (op.getNumResults() == 0)
+      return failure();
+
+    SmallVector<Operation *> yieldOps;
+    for (Block &block : op.getRegion()) {
+      if (auto yield = dyn_cast<scf::YieldOp>(block.getTerminator()))
+        yieldOps.push_back(yield.getOperation());
+    }
+
+    if (yieldOps.empty())
+      return failure();
+
+    // Check if all yield operations have the same operands.
+    auto yieldOpsOperands = yieldOps[0]->getOperands();
+    for (auto *yieldOp : yieldOps) {
+      if (yieldOp->getOperands() != yieldOpsOperands)
+        return failure();
+    }
+
+    SmallVector<Value> externalValues;
+    SmallVector<Value> internalValues;
+    SmallVector<Value> opResultsToReplaceWithExternalValues;
+    SmallVector<Value> opResultsToKeep;
+    for (auto [index, yieldedValue] : llvm::enumerate(yieldOpsOperands)) {
+      if (isValueFromInsideRegion(yieldedValue, op)) {
+        internalValues.push_back(yieldedValue);
+        opResultsToKeep.push_back(op.getResult(index));
+      } else {
+        externalValues.push_back(yieldedValue);
+        opResultsToReplaceWithExternalValues.push_back(op.getResult(index));
+      }
+    }
+    // No yielded external values - nothing to do.
+    if (externalValues.empty())
+      return failure();
+
+    // There are yielded external values - create a new execute_region returning
+    // just the internal values.
+    SmallVector<Type> resultTypes;
+    for (Value value : internalValues)
+      resultTypes.push_back(value.getType());
+    auto newOp =
+        ExecuteRegionOp::create(rewriter, op.getLoc(), TypeRange(resultTypes));
+    newOp->setAttrs(op->getAttrs());
+
+    // Move old op's region to the new operation.
+    rewriter.inlineRegionBefore(op.getRegion(), newOp.getRegion(),
+                                newOp.getRegion().end());
+
+    // Replace all yield operations with a new yield operation with updated
+    // results. scf.execute_region must have at least one yield operation.
+    for (auto *yieldOp : yieldOps) {
+      rewriter.setInsertionPoint(yieldOp);
+      rewriter.replaceOpWithNewOp<scf::YieldOp>(yieldOp,
+                                                ValueRange(internalValues));
+    }
+
+    // Replace the old operation with the external values directly.
+    rewriter.replaceAllUsesWith(opResultsToReplaceWithExternalValues,
+                                externalValues);
+    // Replace the old operation's remaining results with the new operation's
+    // results.
+    rewriter.replaceAllUsesWith(opResultsToKeep, newOp.getResults());
+    rewriter.eraseOp(op);
+    return success();
+  }
+
+private:
+  bool isValueFromInsideRegion(Value value,
+                               ExecuteRegionOp executeRegionOp) const {
+    // Check if the value is defined within the execute_region
+    if (Operation *defOp = value.getDefiningOp())
+      return &executeRegionOp.getRegion() == defOp->getParentRegion();
+
+    // If it's a block argument, check if it's from within the region
+    if (BlockArgument blockArg = dyn_cast<BlockArgument>(value))
+      return &executeRegionOp.getRegion() == blockArg.getParentRegion();
+
+    return false; // Value is from outside the region
+  }
+};
+
 void ExecuteRegionOp::getCanonicalizationPatterns(RewritePatternSet &results,
                                                   MLIRContext *context) {
-  results.add<SingleBlockExecuteInliner, MultiBlockExecuteInliner>(context);
+  results.add<SingleBlockExecuteInliner, MultiBlockExecuteInliner,
+              ExecuteRegionForwardingEliminator>(context);
 }
 
 void ExecuteRegionOp::getSuccessorRegions(