Use rewriter in SCFToSPIRV conversion.

[tpopp]

Summary

Additionally, clear a data structure to ensure a proper state if multiple conversion attempts are needed.

[antiagainst]

Nice, thanks for fixing this!

mlir/lib/Conversion/SCFToSPIRV/SCFToSPIRV.cpp

 static void replaceSCFOutputValue(ScfOp scfOp, OpTy newOp,
                                   SPIRVTypeConverter &typeConverter,
                                   ConversionPatternRewriter &rewriter,
                                   ScfToSPIRVContextImpl *scfToSPIRVContext,
                                   ArrayRef<Type> returnTypes) {
 
   Location loc = scfOp.getLoc();
   auto &allocas = scfToSPIRVContext->outputVars[newOp];
+  // Clearing the allocas is necessary in case a dialect conversion path failed
+  // previously, and this is the second attempt of this conversion.
+  allocas.clear();
   SmallVector<Value, 8> resultValue;
   for (Type convertedType : returnTypes) {
     auto pointerType =
         spirv::PointerType::get(convertedType, spirv::StorageClass::Function);
     rewriter.setInsertionPoint(newOp);
     auto alloc = rewriter.create<spirv::VariableOp>(
         loc, pointerType, spirv::StorageClass::Function,
         /*initializer=*/nullptr);
IfOpConversion::matchAndRewrite(scf::IfOp ifOp, ArrayRef<Value> operands,
   // subsequently converges.
   scf::IfOpAdaptor ifOperands(operands);
   auto loc = ifOp.getLoc();
 
   // Create `spv.selection` operation, selection header block and merge block.
   auto selectionControl = rewriter.getI32IntegerAttr(
       static_cast<uint32_t>(spirv::SelectionControl::None));
   auto selectionOp = rewriter.create<spirv::SelectionOp>(loc, selectionControl);
-  selectionOp.addMergeBlock();
-  auto *mergeBlock = selectionOp.getMergeBlock();
+  auto *mergeBlock =
+      rewriter.createBlock(&selectionOp.body(), selectionOp.body().end());
+  rewriter.create<spirv::MergeOp>(loc);
 
   OpBuilder::InsertionGuard guard(rewriter);
-  auto *selectionHeaderBlock = new Block();
-  selectionOp.body().getBlocks().push_front(selectionHeaderBlock);
+  auto *selectionHeaderBlock =
+      rewriter.createBlock(&selectionOp.body().front());
 
   // Inline `then` region before the merge block and branch to it.
   auto &thenRegion = ifOp.thenRegion();
   auto *thenBlock = &thenRegion.front();
   rewriter.setInsertionPointToEnd(&thenRegion.back());
   rewriter.create<spirv::BranchOp>(loc, mergeBlock);
   rewriter.inlineRegionBefore(thenRegion, mergeBlock);