[mlir][Transforms][NFC] Decouple ConversionPatternRewriterImpl from ConversionPatternRewriter

`ConversionPatternRewriterImpl` no longer maintains a reference to the respective `ConversionPatternRewriter`. An `MLIRContext` is sufficient. This commit simplifies the internal state of `ConversionPatternRewriterImpl`.

Author: matthias-springer

mlir/lib/Transforms/Utils/DialectConversion.cpp

@@ -725,10 +725,9 @@ static RewriteTy *findSingleRewrite(R &&rewrites, Block *block) {
 namespace mlir {
 namespace detail {
 struct ConversionPatternRewriterImpl : public RewriterBase::Listener {
-  explicit ConversionPatternRewriterImpl(PatternRewriter &rewriter,
+  explicit ConversionPatternRewriterImpl(MLIRContext *ctx,
                                          const ConversionConfig &config)
-      : rewriter(rewriter), eraseRewriter(rewriter.getContext()),
-        config(config) {}
+      : eraseRewriter(ctx), config(config) {}
 
   //===--------------------------------------------------------------------===//
   // State Management
@@ -823,8 +822,8 @@ struct ConversionPatternRewriterImpl : public RewriterBase::Listener {
                                        Type origOutputType,
                                        const TypeConverter *converter);
 
-  Value buildUnresolvedArgumentMaterialization(PatternRewriter &rewriter,
-                                               Location loc, ValueRange inputs,
+  Value buildUnresolvedArgumentMaterialization(Block *block, Location loc,
+                                               ValueRange inputs,
                                                Type origOutputType,
                                                Type outputType,
                                                const TypeConverter *converter);
@@ -903,8 +902,6 @@ struct ConversionPatternRewriterImpl : public RewriterBase::Listener {
   // State
   //===--------------------------------------------------------------------===//
 
-  PatternRewriter &rewriter;
-
   /// This rewriter must be used for erasing ops/blocks.
   SingleEraseRewriter eraseRewriter;
 
@@ -1008,8 +1005,12 @@ void BlockTypeConversionRewrite::rollback() {
 
 LogicalResult BlockTypeConversionRewrite::materializeLiveConversions(
     function_ref<Operation *(Value)> findLiveUser) {
+  auto builder = OpBuilder::atBlockBegin(block, /*listener=*/&rewriterImpl);
+
   // Process the remapping for each of the original arguments.
   for (unsigned i = 0, e = origBlock->getNumArguments(); i != e; ++i) {
+    OpBuilder::InsertionGuard g(builder);
+
     // If the type of this argument changed and the argument is still live, we
     // need to materialize a conversion.
     BlockArgument origArg = origBlock->getArgument(i);
@@ -1021,14 +1022,12 @@ LogicalResult BlockTypeConversionRewrite::materializeLiveConversions(
 
     Value replacementValue = rewriterImpl.mapping.lookupOrDefault(origArg);
     bool isDroppedArg = replacementValue == origArg;
-    if (isDroppedArg)
-      rewriterImpl.rewriter.setInsertionPointToStart(getBlock());
-    else
-      rewriterImpl.rewriter.setInsertionPointAfterValue(replacementValue);
+    if (!isDroppedArg)
+      builder.setInsertionPointAfterValue(replacementValue);
     Value newArg;
     if (converter) {
       newArg = converter->materializeSourceConversion(
-          rewriterImpl.rewriter, origArg.getLoc(), origArg.getType(),
+          builder, origArg.getLoc(), origArg.getType(),
           isDroppedArg ? ValueRange() : ValueRange(replacementValue));
       assert((!newArg || newArg.getType() == origArg.getType()) &&
              "materialization hook did not provide a value of the expected "
@@ -1293,6 +1292,8 @@ LogicalResult ConversionPatternRewriterImpl::convertNonEntryRegionTypes(
 Block *ConversionPatternRewriterImpl::applySignatureConversion(
     Block *block, const TypeConverter *converter,
     TypeConverter::SignatureConversion &signatureConversion) {
+  MLIRContext *ctx = block->getParentOp()->getContext();
+
   // If no arguments are being changed or added, there is nothing to do.
   unsigned origArgCount = block->getNumArguments();
   auto convertedTypes = signatureConversion.getConvertedTypes();
@@ -1309,7 +1310,7 @@ Block *ConversionPatternRewriterImpl::applySignatureConversion(
 
   // Map all new arguments to the location of the argument they originate from.
   SmallVector<Location> newLocs(convertedTypes.size(),
-                                rewriter.getUnknownLoc());
+                                Builder(ctx).getUnknownLoc());
   for (unsigned i = 0; i < origArgCount; ++i) {
     auto inputMap = signatureConversion.getInputMapping(i);
     if (!inputMap || inputMap->replacementValue)
@@ -1328,8 +1329,6 @@ Block *ConversionPatternRewriterImpl::applySignatureConversion(
   SmallVector<std::optional<ConvertedArgInfo>, 1> argInfo;
   argInfo.resize(origArgCount);
 
-  OpBuilder::InsertionGuard guard(rewriter);
-  rewriter.setInsertionPointToStart(newBlock);
   for (unsigned i = 0; i != origArgCount; ++i) {
     auto inputMap = signatureConversion.getInputMapping(i);
     if (!inputMap)
@@ -1372,7 +1371,7 @@ Block *ConversionPatternRewriterImpl::applySignatureConversion(
         outputType = legalOutputType;
 
       newArg = buildUnresolvedArgumentMaterialization(
-          rewriter, origArg.getLoc(), replArgs, origOutputType, outputType,
+          newBlock, origArg.getLoc(), replArgs, origOutputType, outputType,
           converter);
     }
 
@@ -1410,12 +1409,11 @@ Value ConversionPatternRewriterImpl::buildUnresolvedMaterialization(
   return convertOp.getResult(0);
 }
 Value ConversionPatternRewriterImpl::buildUnresolvedArgumentMaterialization(
-    PatternRewriter &rewriter, Location loc, ValueRange inputs,
-    Type origOutputType, Type outputType, const TypeConverter *converter) {
-  return buildUnresolvedMaterialization(
-      MaterializationKind::Argument, rewriter.getInsertionBlock(),
-      rewriter.getInsertionPoint(), loc, inputs, outputType, origOutputType,
-      converter);
+    Block *block, Location loc, ValueRange inputs, Type origOutputType,
+    Type outputType, const TypeConverter *converter) {
+  return buildUnresolvedMaterialization(MaterializationKind::Argument, block,
+                                        block->begin(), loc, inputs, outputType,
+                                        origOutputType, converter);
 }
 Value ConversionPatternRewriterImpl::buildUnresolvedTargetMaterialization(
     Location loc, Value input, Type outputType,
@@ -1527,7 +1525,7 @@ void ConversionPatternRewriterImpl::notifyMatchFailure(
 ConversionPatternRewriter::ConversionPatternRewriter(
     MLIRContext *ctx, const ConversionConfig &config)
     : PatternRewriter(ctx),
-      impl(new detail::ConversionPatternRewriterImpl(*this, config)) {
+      impl(new detail::ConversionPatternRewriterImpl(ctx, config)) {
   setListener(impl.get());
 }