[Mlir-commits] [mlir] [MLIR][SCF] fix scf.index_switch fold convergence (#98535) (PR #98680)

[Mehdi Amini]

================
@@ -4297,33 +4297,38 @@ void IndexSwitchOp::getRegionInvocationBounds(
     bounds.emplace_back(/*lb=*/0, /*ub=*/i == liveIndex);
 }
 
-LogicalResult IndexSwitchOp::fold(FoldAdaptor adaptor,
-                                  SmallVectorImpl<OpFoldResult> &results) {
-  std::optional<int64_t> maybeCst = getConstantIntValue(getArg());
-  if (!maybeCst.has_value())
-    return failure();
-  int64_t cst = *maybeCst;
-  int64_t caseIdx, e = getNumCases();
-  for (caseIdx = 0; caseIdx < e; ++caseIdx) {
-    if (cst == getCases()[caseIdx])
-      break;
-  }
+struct FoldConstantCase : OpRewritePattern<scf::IndexSwitchOp> {
+  using OpRewritePattern<scf::IndexSwitchOp>::OpRewritePattern;
 
-  Region &r = (caseIdx < getNumCases()) ? getCaseRegions()[caseIdx]
-                                        : getDefaultRegion();
-  Block &source = r.front();
-  results.assign(source.getTerminator()->getOperands().begin(),
-                 source.getTerminator()->getOperands().end());
+  LogicalResult matchAndRewrite(scf::IndexSwitchOp op,
+                                PatternRewriter &rewriter) const override {
+    std::optional<int64_t> maybeCst = getConstantIntValue(op.getArg());
+    if (!maybeCst.has_value())
+      return failure();
+    int64_t cst = *maybeCst;
+    int64_t caseIdx, e = op.getNumCases();
+    for (caseIdx = 0; caseIdx < e; ++caseIdx) {
+      if (cst == op.getCases()[caseIdx])
+        break;
+    }
 
-  Block *pDestination = (*this)->getBlock();
-  if (!pDestination)
-    return failure();
-  Block::iterator insertionPoint = (*this)->getIterator();
-  pDestination->getOperations().splice(insertionPoint, source.getOperations(),
-                                       source.getOperations().begin(),
-                                       std::prev(source.getOperations().end()));
+    Region &r = (caseIdx < op.getNumCases()) ? op.getCaseRegions()[caseIdx]
+                                             : op.getDefaultRegion();
+    Block &source = r.front();
+    Operation *terminator = source.getTerminator();
+    SmallVector<Value> results = terminator->getOperands();
 
-  return success();
+    rewriter.inlineBlockBefore(&source, op);
+    rewriter.eraseOp(terminator);
+    rewriter.replaceOp(op, results);
+
+    return success();
+  }
----------------
joker-eph wrote:

Can we add some comment in here?
Otherwise this seems OK.


https://github.com/llvm/llvm-project/pull/98680