[flang] Remove materialization workaround in type converter

This change is in preparation of #97903, which adds extra checks for materializations: it is now enforced that they produce an SSA value of the correct type, so the current workaround no longer works.

For `fir.has_value` the fix is simple: no target materializations on the operands are performed if the lowering patterns is initialized without a type converter. For `cg::XEmboxOp`, the existing workaround that skips `unrealized_conversion_cast` ops can be generalized. (This is still a workaround.)

Also remove the lowering pattern for `unrealized_conversion_cast`. This pattern has no effect because `unrealized_conversion_cast` ops that are inserted by the dialect conversion framework are never matched by the pattern driver.

flang/include/flang/Tools/CLOptions.inc

@@ -9,6 +9,7 @@
 /// This file defines some shared command-line options that can be used when
 /// debugging the test tools. This file must be included into the tool.
 
+#include "mlir/Conversion/ReconcileUnrealizedCasts/ReconcileUnrealizedCasts.h"
 #include "mlir/Conversion/SCFToControlFlow/SCFToControlFlow.h"
 #include "mlir/Dialect/LLVMIR/LLVMAttrs.h"
 #include "mlir/Pass/PassManager.h"
@@ -223,6 +224,10 @@ inline void addFIRToLLVMPass(
   options.forceUnifiedTBAATree = useOldAliasTags;
   addPassConditionally(pm, disableFirToLlvmIr,
       [&]() { return fir::createFIRToLLVMPass(options); });
+  // The dialect conversion framework may leave dead unrealized_conversion_cast
+  // ops behind, so run reconcile-unrealized-casts to clean them up.
+  addPassConditionally(pm, disableFirToLlvmIr,
+      [&]() { return mlir::createReconcileUnrealizedCastsPass(); });
 }
 
 inline void addLLVMDialectToLLVMPass(

flang/lib/Optimizer/CodeGen/CodeGen.cpp

@@ -35,7 +35,6 @@
 #include "mlir/Conversion/MathToLLVM/MathToLLVM.h"
 #include "mlir/Conversion/MathToLibm/MathToLibm.h"
 #include "mlir/Conversion/OpenMPToLLVM/ConvertOpenMPToLLVM.h"
-#include "mlir/Conversion/ReconcileUnrealizedCasts/ReconcileUnrealizedCasts.h"
 #include "mlir/Conversion/VectorToLLVM/ConvertVectorToLLVM.h"
 #include "mlir/Dialect/Arith/IR/Arith.h"
 #include "mlir/Dialect/DLTI/DLTI.h"
@@ -1726,10 +1725,9 @@ struct XReboxOpConversion : public EmboxCommonConversion<fir::cg::XReboxOp> {
     // fir.box was translated to an llvm.ptr<llvm.struct<>> and the MLIR pass
     // manager inserted a builtin.unrealized_conversion_cast that was inserted
     // and needs to be removed here.
-    if (isInGlobalOp(rewriter))
-      if (auto unrealizedCast =
-              loweredBox.getDefiningOp<mlir::UnrealizedConversionCastOp>())
-        loweredBox = unrealizedCast.getInputs()[0];
+    if (auto unrealizedCast =
+            loweredBox.getDefiningOp<mlir::UnrealizedConversionCastOp>())
+      loweredBox = unrealizedCast.getInputs()[0];
 
     TypePair inputBoxTyPair = getBoxTypePair(rebox.getBox().getType());
 
@@ -2669,8 +2667,9 @@ struct TypeDescOpConversion : public fir::FIROpConversion<fir::TypeDescOp> {
 };
 
 /// Lower `fir.has_value` operation to `llvm.return` operation.
-struct HasValueOpConversion : public fir::FIROpConversion<fir::HasValueOp> {
-  using FIROpConversion::FIROpConversion;
+struct HasValueOpConversion
+    : public mlir::OpConversionPattern<fir::HasValueOp> {
+  using OpConversionPattern::OpConversionPattern;
 
   llvm::LogicalResult
   matchAndRewrite(fir::HasValueOp op, OpAdaptor adaptor,
@@ -3515,29 +3514,6 @@ struct MustBeDeadConversion : public fir::FIROpConversion<FromOp> {
   }
 };
 
-struct UnrealizedConversionCastOpConversion
-    : public fir::FIROpConversion<mlir::UnrealizedConversionCastOp> {
-  using FIROpConversion::FIROpConversion;
-
-  llvm::LogicalResult
-  matchAndRewrite(mlir::UnrealizedConversionCastOp op, OpAdaptor adaptor,
-                  mlir::ConversionPatternRewriter &rewriter) const override {
-    assert(op.getOutputs().getTypes().size() == 1 && "expect a single type");
-    mlir::Type convertedType = convertType(op.getOutputs().getTypes()[0]);
-    if (convertedType == adaptor.getInputs().getTypes()[0]) {
-      rewriter.replaceOp(op, adaptor.getInputs());
-      return mlir::success();
-    }
-
-    convertedType = adaptor.getInputs().getTypes()[0];
-    if (convertedType == op.getOutputs().getType()[0]) {
-      rewriter.replaceOp(op, adaptor.getInputs());
-      return mlir::success();
-    }
-    return mlir::failure();
-  }
-};
-
 struct ShapeOpConversion : public MustBeDeadConversion<fir::ShapeOp> {
   using MustBeDeadConversion::MustBeDeadConversion;
 };
@@ -3714,7 +3690,8 @@ class FIRToLLVMLowering
       signalPassFailure();
     }
 
-    // Run pass to add comdats to functions that have weak linkage on relevant platforms
+    // Run pass to add comdats to functions that have weak linkage on relevant
+    // platforms
     if (fir::getTargetTriple(mod).supportsCOMDAT()) {
       mlir::OpPassManager comdatPM("builtin.module");
       comdatPM.addPass(mlir::LLVM::createLLVMAddComdats());
@@ -3789,16 +3766,17 @@ void fir::populateFIRToLLVMConversionPatterns(
       DivcOpConversion, EmboxOpConversion, EmboxCharOpConversion,
       EmboxProcOpConversion, ExtractValueOpConversion, FieldIndexOpConversion,
       FirEndOpConversion, FreeMemOpConversion, GlobalLenOpConversion,
-      GlobalOpConversion, HasValueOpConversion, InsertOnRangeOpConversion,
-      InsertValueOpConversion, IsPresentOpConversion, LenParamIndexOpConversion,
-      LoadOpConversion, MulcOpConversion, NegcOpConversion,
-      NoReassocOpConversion, SelectCaseOpConversion, SelectOpConversion,
-      SelectRankOpConversion, SelectTypeOpConversion, ShapeOpConversion,
-      ShapeShiftOpConversion, ShiftOpConversion, SliceOpConversion,
-      StoreOpConversion, StringLitOpConversion, SubcOpConversion,
-      TypeDescOpConversion, TypeInfoOpConversion, UnboxCharOpConversion,
-      UnboxProcOpConversion, UndefOpConversion, UnreachableOpConversion,
-      UnrealizedConversionCastOpConversion, XArrayCoorOpConversion,
+      GlobalOpConversion, InsertOnRangeOpConversion, InsertValueOpConversion,
+      IsPresentOpConversion, LenParamIndexOpConversion, LoadOpConversion,
+      MulcOpConversion, NegcOpConversion, NoReassocOpConversion,
+      SelectCaseOpConversion, SelectOpConversion, SelectRankOpConversion,
+      SelectTypeOpConversion, ShapeOpConversion, ShapeShiftOpConversion,
+      ShiftOpConversion, SliceOpConversion, StoreOpConversion,
+      StringLitOpConversion, SubcOpConversion, TypeDescOpConversion,
+      TypeInfoOpConversion, UnboxCharOpConversion, UnboxProcOpConversion,
+      UndefOpConversion, UnreachableOpConversion, XArrayCoorOpConversion,
       XEmboxOpConversion, XReboxOpConversion, ZeroOpConversion>(converter,
                                                                 options);
+
+  patterns.insert<HasValueOpConversion>(patterns.getContext());
 }

flang/test/Fir/basic-program.fir

@@ -119,4 +119,5 @@ func.func @_QQmain() {
 // PASSES-NEXT:   (S) 0 num-dce'd - Number of operations eliminated
 // PASSES-NEXT: TargetRewrite
 // PASSES-NEXT: FIRToLLVMLowering
+// PASSES-NEXT: ReconcileUnrealizedCasts
 // PASSES-NEXT: LLVMIRLoweringPass