[Mlir-commits] [mlir] [MLIR][Conversion] Remove func dialect dependency for CF to SCF conversion (PR #222594)

[Tobias Gysi]

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@@ -421,15 +421,35 @@ class ReturnLikeExitCombiner {
   /// Transforms `returnLikeOp` to a branch to the only block in the
   /// region with an instance of `returnLikeOp`s kind.
   void combineExit(Operation *returnLikeOp,
-                   function_ref<Value(unsigned)> getSwitchValue) {
-    auto [iter, inserted] = returnLikeToCombinedExit.try_emplace(returnLikeOp);
-    if (!inserted && iter->first == returnLikeOp)
+                   function_ref<Value(unsigned)> getSwitchValue,
+                   function_ref<Value(Type)> getUndefValue) {
+    auto existing = returnLikeToCombinedExit.find(returnLikeOp);
+    if (existing != returnLikeToCombinedExit.end() &&
+        existing->first == returnLikeOp)
       return;
 
+    // If `returnLikeOp` is an unreachable terminator and an exit block of
+    // another return-like operation already exists, it is turned into a branch
+    // to that exit block with undefined operands instead of getting an exit
+    // block of its own.
+    if (interface.isUnreachableTerminator(returnLikeOp) &&
+        !orderedExitBlocks.empty()) {
+      Block *exitBlock = orderedExitBlocks.front();
+      auto builder = OpBuilder::atBlockTerminator(returnLikeOp->getBlock());
+      interface.createSingleDestinationBranch(
+          returnLikeOp->getLoc(), builder, getSwitchValue(0), exitBlock,
+          llvm::map_to_vector(exitBlock->getArgumentTypes(), getUndefValue));
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gysit wrote:

nit: it could make sense to rename `getUndefValue` to `getPoisonValue`. It seems like it changed from producing undef to producing poison at some time but the helper itself was never renamed. 

https://github.com/llvm/llvm-project/pull/222594