[mlir] Dialect conversion: Print note when replacement types do not match legalized types (#161802)

When running with `-debug`, print a note when the replacement types
(during a `ConversionPatternRewriter::replaceOp`) do not match the
legalized types of the current type converter. That's not an API
violation, but it could indicate a bug in user code.

Example output:
```
[dialect-conversion:1]     ** Replace : 'test.multiple_1_to_n_replacement'(0x56b745f99470)
[dialect-conversion:1]        Note: Replacing op result of type f16 with value(s) of type (f16, f16), but the legalized type(s) is/are (f16)
```

Author: matthias-springer

mlir/lib/Transforms/Utils/DialectConversion.cpp

@@ -1856,6 +1856,44 @@ void ConversionPatternRewriterImpl::replaceOp(
     Operation *op, SmallVector<SmallVector<Value>> &&newValues) {
   assert(newValues.size() == op->getNumResults() &&
          "incorrect number of replacement values");
+  LLVM_DEBUG({
+    logger.startLine() << "** Replace : '" << op->getName() << "'(" << op
+                       << ")\n";
+    if (currentTypeConverter) {
+      // If the user-provided replacement types are different from the
+      // legalized types, as per the current type converter, print a note.
+      // In most cases, the replacement types are expected to match the types
+      // produced by the type converter, so this could indicate a bug in the
+      // user code.
+      for (auto [result, repls] :
+           llvm::zip_equal(op->getResults(), newValues)) {
+        Type resultType = result.getType();
+        auto logProlog = [&, repls = repls]() {
+          logger.startLine() << "   Note: Replacing op result of type "
+                             << resultType << " with value(s) of type (";
+          llvm::interleaveComma(repls, logger.getOStream(), [&](Value v) {
+            logger.getOStream() << v.getType();
+          });
+          logger.getOStream() << ")";
+        };
+        SmallVector<Type> convertedTypes;
+        if (failed(currentTypeConverter->convertTypes(resultType,
+                                                      convertedTypes))) {
+          logProlog();
+          logger.getOStream() << ", but the type converter failed to legalize "
+                                 "the original type.\n";
+          continue;
+        }
+        if (TypeRange(convertedTypes) != TypeRange(ValueRange(repls))) {
+          logProlog();
+          logger.getOStream() << ", but the legalized type(s) is/are (";
+          llvm::interleaveComma(convertedTypes, logger.getOStream(),
+                                [&](Type t) { logger.getOStream() << t; });
+          logger.getOStream() << ")\n";
+        }
+      }
+    }
+  });
 
   if (!config.allowPatternRollback) {
     // Pattern rollback is not allowed: materialize all IR changes immediately.
@@ -2072,10 +2110,6 @@ void ConversionPatternRewriter::replaceOp(Operation *op, Operation *newOp) {
 void ConversionPatternRewriter::replaceOp(Operation *op, ValueRange newValues) {
   assert(op->getNumResults() == newValues.size() &&
          "incorrect # of replacement values");
-  LLVM_DEBUG({
-    impl->logger.startLine()
-        << "** Replace : '" << op->getName() << "'(" << op << ")\n";
-  });
 
   // If the current insertion point is before the erased operation, we adjust
   // the insertion point to be after the operation.
@@ -2093,10 +2127,6 @@ void ConversionPatternRewriter::replaceOpWithMultiple(
     Operation *op, SmallVector<SmallVector<Value>> &&newValues) {
   assert(op->getNumResults() == newValues.size() &&
          "incorrect # of replacement values");
-  LLVM_DEBUG({
-    impl->logger.startLine()
-        << "** Replace : '" << op->getName() << "'(" << op << ")\n";
-  });
 
   // If the current insertion point is before the erased operation, we adjust
   // the insertion point to be after the operation.