[llvm-branch-commits] [mlir] [mlir][SCF] Fold unused `index_switch` results (PR #173560)

[lonely eagle via llvm-branch-commits]

================
@@ -4797,9 +4797,59 @@ struct FoldConstantCase : OpRewritePattern<scf::IndexSwitchOp> {
   }
 };
 
+/// Canonicalization patterns that folds away dead results of
+/// "scf.index_switch" ops.
+struct FoldUnusedIndexSwitchResults : OpRewritePattern<IndexSwitchOp> {
+  using OpRewritePattern<IndexSwitchOp>::OpRewritePattern;
+
+  LogicalResult matchAndRewrite(IndexSwitchOp op,
+                                PatternRewriter &rewriter) const override {
+    // Find dead results.
+    BitVector deadResults(op.getNumResults(), false);
+    SmallVector<Type> newResultTypes;
+    for (auto [idx, result] : llvm::enumerate(op.getResults())) {
+      if (!result.use_empty()) {
+        newResultTypes.push_back(result.getType());
+      } else {
+        deadResults[idx] = true;
+      }
+    }
+    if (!deadResults.any())
+      return rewriter.notifyMatchFailure(op, "no dead results to fold");
+
+    // Create new op without dead results and inline case regions.
+    auto newOp = IndexSwitchOp::create(rewriter, op.getLoc(), newResultTypes,
+                                       op.getArg(), op.getCases(),
+                                       op.getCaseRegions().size());
+    auto inlineCaseRegion = [&](Region &oldRegion, Region &newRegion) {
+      rewriter.inlineRegionBefore(oldRegion, newRegion, newRegion.begin());
+      // Remove respective operands from yield op.
+      Operation *terminator = newRegion.front().getTerminator();
+      assert(isa<YieldOp>(terminator) && "expected yield op");
+      rewriter.modifyOpInPlace(
+          terminator, [&]() { terminator->eraseOperands(deadResults); });
+    };
+    for (auto [oldRegion, newRegion] :
+         llvm::zip_equal(op.getCaseRegions(), newOp.getCaseRegions()))
+      inlineCaseRegion(oldRegion, newRegion);
+    inlineCaseRegion(op.getDefaultRegion(), newOp.getDefaultRegion());
+
+    // Replace op with new op.
+    SmallVector<Value> newResults(op.getNumResults(), Value());
+    unsigned nextNewResult = 0;
+    for (unsigned idx = 0; idx < op.getNumResults(); ++idx) {
----------------
linuxlonelyeagle wrote:

```suggestion
    for (unsigned idx = 0, e = op.getNumResults(); idx < e; ++idx) {
```

https://github.com/llvm/llvm-project/pull/173560