Revert "Bump LLVM to llvm/llvm-project@6c64c8a6f3f7 (#3818)"

This reverts commit 8b0bf2e.

lib/Dialect/TorchConversion/Transforms/BackendTypeConversion.cpp

@@ -57,16 +57,16 @@ static void setupTorchBoolToI1Conversion(ConversionTarget &target,
   typeConverter.addConversion([](Torch::BoolType type) -> std::optional<Type> {
     return IntegerType::get(type.getContext(), 1);
   });
-  typeConverter.addTargetMaterialization([](OpBuilder &builder,
-                                            IntegerType type, ValueRange inputs,
-                                            Location loc) -> Value {
-    // Other builtin integer types could be handled by other materializers.
-    if (!(type.getWidth() == 1 && type.isSignless()))
-      return Value();
-    assert(inputs.size() == 1);
-    assert(isa<Torch::BoolType>(inputs[0].getType()));
-    return builder.create<ToI1Op>(loc, inputs[0]).getResult();
-  });
+  typeConverter.addTargetMaterialization(
+      [](OpBuilder &builder, IntegerType type, ValueRange inputs,
+         Location loc) -> std::optional<Value> {
+        // Other builtin integer types could be handled by other materializers.
+        if (!(type.getWidth() == 1 && type.isSignless()))
+          return std::nullopt;
+        assert(inputs.size() == 1);
+        assert(isa<Torch::BoolType>(inputs[0].getType()));
+        return builder.create<ToI1Op>(loc, inputs[0]).getResult();
+      });
   auto sourceMaterialization = [](OpBuilder &builder, Torch::BoolType type,
                                   ValueRange inputs, Location loc) -> Value {
     assert(inputs.size() == 1);
@@ -83,19 +83,19 @@ static void setupTorchIntToI64Conversion(ConversionTarget &target,
   typeConverter.addConversion([](Torch::IntType type) -> std::optional<Type> {
     return IntegerType::get(type.getContext(), 64);
   });
-  typeConverter.addTargetMaterialization([](OpBuilder &builder,
-                                            IntegerType type, ValueRange inputs,
-                                            Location loc) -> Value {
-    // Other builtin integer types could be handled by other materializers.
-    if (!(type.getWidth() == 64 && type.isSignless()))
-      return Value();
-    // Other input type to be converted to i64 are handled by other
-    // materializers.
-    if (!isa<Torch::IntType>(inputs[0].getType()))
-      return Value();
-    assert(inputs.size() == 1);
-    return builder.createOrFold<ToI64Op>(loc, inputs[0]);
-  });
+  typeConverter.addTargetMaterialization(
+      [](OpBuilder &builder, IntegerType type, ValueRange inputs,
+         Location loc) -> std::optional<Value> {
+        // Other builtin integer types could be handled by other materializers.
+        if (!(type.getWidth() == 64 && type.isSignless()))
+          return std::nullopt;
+        // Other input type to be converted to i64 are handled by other
+        // materializers.
+        if (!isa<Torch::IntType>(inputs[0].getType()))
+          return std::nullopt;
+        assert(inputs.size() == 1);
+        return builder.createOrFold<ToI64Op>(loc, inputs[0]);
+      });
   auto sourceMaterialization = [](OpBuilder &builder, Torch::IntType type,
                                   ValueRange inputs, Location loc) -> Value {
     assert(inputs.size() == 1);
@@ -112,13 +112,13 @@ static void setupTorchFloatToF64Conversion(ConversionTarget &target,
   typeConverter.addConversion([](Torch::FloatType type) -> std::optional<Type> {
     return Float64Type::get(type.getContext());
   });
-  typeConverter.addTargetMaterialization([](OpBuilder &builder,
-                                            Float64Type type, ValueRange inputs,
-                                            Location loc) -> Value {
-    assert(inputs.size() == 1);
-    assert(isa<Torch::FloatType>(inputs[0].getType()));
-    return builder.create<ToF64Op>(loc, inputs[0]).getResult();
-  });
+  typeConverter.addTargetMaterialization(
+      [](OpBuilder &builder, Float64Type type, ValueRange inputs,
+         Location loc) -> std::optional<Value> {
+        assert(inputs.size() == 1);
+        assert(isa<Torch::FloatType>(inputs[0].getType()));
+        return builder.create<ToF64Op>(loc, inputs[0]).getResult();
+      });
   auto sourceMaterialization = [](OpBuilder &builder, Torch::FloatType type,
                                   ValueRange inputs, Location loc) -> Value {
     assert(inputs.size() == 1);
@@ -137,19 +137,19 @@ static void setupTorchGeneratorToI64Conversion(ConversionTarget &target,
       [](Torch::GeneratorType type) -> std::optional<Type> {
         return IntegerType::get(type.getContext(), 64);
       });
-  typeConverter.addTargetMaterialization([](OpBuilder &builder,
-                                            IntegerType type, ValueRange inputs,
-                                            Location loc) -> Value {
-    // Other builtin integer types could be handled by other materializers.
-    if (!(type.getWidth() == 64 && type.isSignless()))
-      return Value();
-    // Other input type to be converted to i64 are handled by other
-    // materializers.
-    if (!isa<Torch::GeneratorType>(inputs[0].getType()))
-      return Value();
-    assert(inputs.size() == 1);
-    return builder.create<GeneratorToI64Op>(loc, inputs[0]).getResult();
-  });
+  typeConverter.addTargetMaterialization(
+      [](OpBuilder &builder, IntegerType type, ValueRange inputs,
+         Location loc) -> std::optional<Value> {
+        // Other builtin integer types could be handled by other materializers.
+        if (!(type.getWidth() == 64 && type.isSignless()))
+          return std::nullopt;
+        // Other input type to be converted to i64 are handled by other
+        // materializers.
+        if (!isa<Torch::GeneratorType>(inputs[0].getType()))
+          return std::nullopt;
+        assert(inputs.size() == 1);
+        return builder.create<GeneratorToI64Op>(loc, inputs[0]).getResult();
+      });
   auto sourceMaterialization = [](OpBuilder &builder, Torch::GeneratorType type,
                                   ValueRange inputs, Location loc) -> Value {
     assert(inputs.size() == 1);