[mlir][Transforms] Dialect conversion: extra signature conversion check

mlir/lib/Transforms/Utils/DialectConversion.cpp

@@ -434,23 +434,25 @@ class MoveBlockRewrite : public BlockRewrite {
 class BlockTypeConversionRewrite : public BlockRewrite {
 public:
   BlockTypeConversionRewrite(ConversionPatternRewriterImpl &rewriterImpl,
-                             Block *block, Block *origBlock)
-      : BlockRewrite(Kind::BlockTypeConversion, rewriterImpl, block),
-        origBlock(origBlock) {}
+                             Block *origBlock, Block *newBlock)
+      : BlockRewrite(Kind::BlockTypeConversion, rewriterImpl, origBlock),
+        newBlock(newBlock) {}
 
   static bool classof(const IRRewrite *rewrite) {
     return rewrite->getKind() == Kind::BlockTypeConversion;
   }
 
-  Block *getOrigBlock() const { return origBlock; }
+  Block *getOrigBlock() const { return block; }
+
+  Block *getNewBlock() const { return newBlock; }
 
   void commit(RewriterBase &rewriter) override;
 
   void rollback() override;
 
 private:
-  /// The original block that was requested to have its signature converted.
-  Block *origBlock;
+  /// The new block that was created as part of this signature conversion.
+  Block *newBlock;
 };
 
 /// Replacing a block argument. This rewrite is not immediately reflected in the
@@ -721,6 +723,18 @@ static bool hasRewrite(R &&rewrites, Operation *op) {
   });
 }
 
+#ifndef NDEBUG
+/// Return "true" if there is a block rewrite that matches the specified
+/// rewrite type and block among the given rewrites.
+template <typename RewriteTy, typename R>
+static bool hasRewrite(R &&rewrites, Block *block) {
+  return any_of(std::forward<R>(rewrites), [&](auto &rewrite) {
+    auto *rewriteTy = dyn_cast<RewriteTy>(rewrite.get());
+    return rewriteTy && rewriteTy->getBlock() == block;
+  });
+}
+#endif // NDEBUG
+
 //===----------------------------------------------------------------------===//
 // ConversionPatternRewriterImpl
 //===----------------------------------------------------------------------===//
@@ -966,12 +980,12 @@ void BlockTypeConversionRewrite::commit(RewriterBase &rewriter) {
   // block.
   if (auto *listener =
           dyn_cast_or_null<RewriterBase::Listener>(rewriter.getListener()))
-    for (Operation *op : block->getUsers())
+    for (Operation *op : getNewBlock()->getUsers())
       listener->notifyOperationModified(op);
 }
 
 void BlockTypeConversionRewrite::rollback() {
-  block->replaceAllUsesWith(origBlock);
+  getNewBlock()->replaceAllUsesWith(getOrigBlock());
 }
 
 void ReplaceBlockArgRewrite::commit(RewriterBase &rewriter) {
@@ -1223,6 +1237,9 @@ Block *ConversionPatternRewriterImpl::applySignatureConversion(
     ConversionPatternRewriter &rewriter, Block *block,
     const TypeConverter *converter,
     TypeConverter::SignatureConversion &signatureConversion) {
+  // A block cannot be converted multiple times.
+  assert(!hasRewrite<BlockTypeConversionRewrite>(rewrites, block) &&
+         "block was already converted");
   OpBuilder::InsertionGuard g(rewriter);
 
   // If no arguments are being changed or added, there is nothing to do.
@@ -1308,7 +1325,7 @@ Block *ConversionPatternRewriterImpl::applySignatureConversion(
     appendRewrite<ReplaceBlockArgRewrite>(block, origArg, converter);
   }
 
-  appendRewrite<BlockTypeConversionRewrite>(newBlock, block);
+  appendRewrite<BlockTypeConversionRewrite>(/*origBlock=*/block, newBlock);
 
   // Erase the old block. (It is just unlinked for now and will be erased during
   // cleanup.)