[mlir] Simplify Default cases in type switches. NFC. (#165767)

Use default values instead of lambdas when possible. `std::nullopt` and
`nullptr` can be used now because of
#165724.

Author: kuhar

mlir/lib/Conversion/AMDGPUToROCDL/AMDGPUToROCDL.cpp

@@ -935,7 +935,7 @@ static std::optional<uint32_t> mfmaTypeSelectCode(Type mlirElemType) {
       .Case([](Float6E2M3FNType) { return 2u; })
       .Case([](Float6E3M2FNType) { return 3u; })
       .Case([](Float4E2M1FNType) { return 4u; })
-      .Default([](Type) { return std::nullopt; });
+      .Default(std::nullopt);
 }
 
 /// If there is a scaled MFMA instruction for the input element types `aType`

mlir/lib/Conversion/ArithToAMDGPU/ArithToAMDGPU.cpp

@@ -432,7 +432,7 @@ static Value getOriginalVectorValue(Value value) {
                         current = op.getSource();
                         return false;
                       })
-                      .Default([](Operation *) { return false; });
+                      .Default(false);
 
     if (!skipOp) {
       break;

mlir/lib/Conversion/GPUToLLVMSPV/GPUToLLVMSPV.cpp

@@ -259,7 +259,7 @@ struct GPUShuffleConversion final : ConvertOpToLLVMPattern<gpu::ShuffleOp> {
           }
           return std::nullopt;
         })
-        .Default([](auto) { return std::nullopt; });
+        .Default(std::nullopt);
   }
 
   static std::optional<std::string> getFuncName(gpu::ShuffleMode mode,

mlir/lib/Conversion/VectorToXeGPU/VectorToXeGPU.cpp

@@ -46,7 +46,7 @@ static bool isZeroConstant(Value val) {
           [](auto floatAttr) { return floatAttr.getValue().isZero(); })
       .Case<IntegerAttr>(
           [](auto intAttr) { return intAttr.getValue().isZero(); })
-      .Default([](auto) { return false; });
+      .Default(false);
 }
 
 static LogicalResult storeLoadPreconditions(PatternRewriter &rewriter,

mlir/lib/Dialect/Arith/IR/ArithOps.cpp

@@ -2751,7 +2751,7 @@ std::optional<TypedAttr> mlir::arith::getNeutralElement(Operation *op) {
           .Case([](arith::MaxSIOp op) { return AtomicRMWKind::maxs; })
           .Case([](arith::MinSIOp op) { return AtomicRMWKind::mins; })
           .Case([](arith::MulIOp op) { return AtomicRMWKind::muli; })
-          .Default([](Operation *op) { return std::nullopt; });
+          .Default(std::nullopt);
   if (!maybeKind) {
     return std::nullopt;
   }

mlir/lib/Dialect/GPU/Transforms/EliminateBarriers.cpp

@@ -330,7 +330,7 @@ static Value getBase(Value v) {
               v = op.getSrc();
               return true;
             })
-            .Default([](Operation *) { return false; });
+            .Default(false);
     if (!shouldContinue)
       break;
   }
@@ -354,7 +354,7 @@ static Value propagatesCapture(Operation *op) {
       .Case([](memref::TransposeOp transpose) { return transpose.getIn(); })
       .Case<memref::ExpandShapeOp, memref::CollapseShapeOp>(
           [](auto op) { return op.getSrc(); })
-      .Default([](Operation *) { return Value(); });
+      .Default(nullptr);
 }
 
 /// Returns `true` if the given operation is known to capture the given value,
@@ -371,7 +371,7 @@ static std::optional<bool> getKnownCapturingStatus(Operation *op, Value v) {
       // These operations are known not to capture.
       .Case([](memref::DeallocOp) { return false; })
       // By default, we don't know anything.
-      .Default([](Operation *) { return std::nullopt; });
+      .Default(std::nullopt);
 }
 
 /// Returns `true` if the value may be captured by any of its users, i.e., if

mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp

@@ -698,7 +698,7 @@ static void destructureIndices(Type currType, ArrayRef<GEPArg> indices,
                        return structType.getBody()[memberIndex];
                      return nullptr;
                    })
-                   .Default(Type(nullptr));
+                   .Default(nullptr);
   }
 }
 

mlir/lib/Dialect/LLVMIR/IR/LLVMMemorySlot.cpp

@@ -1111,7 +1111,7 @@ memsetCanUsesBeRemoved(MemsetIntr op, const MemorySlot &slot,
           .Case<IntegerType, FloatType>([](auto type) {
             return type.getWidth() % 8 == 0 && type.getWidth() > 0;
           })
-          .Default([](Type) { return false; });
+          .Default(false);
   if (!canConvertType)
     return false;
 

mlir/lib/Dialect/LLVMIR/IR/LLVMTypes.cpp

@@ -798,7 +798,7 @@ static bool isCompatibleImpl(Type type, DenseSet<Type> &compatibleTypes) {
           // clang-format on
           .Case<PtrLikeTypeInterface>(
               [](Type type) { return isCompatiblePtrType(type); })
-          .Default([](Type) { return false; });
+          .Default(false);
 
   if (!result)
     compatibleTypes.erase(type);

mlir/lib/Dialect/Linalg/TransformOps/LinalgTransformOps.cpp

@@ -4499,7 +4499,7 @@ DiagnosedSilenceableFailure transform::DecomposeWinogradOp::applyToOne(
             maybeTransformed = decomposeWinogradOutputTransformOp(rewriter, op);
             return true;
           })
-          .Default([&](Operation *op) { return false; });
+          .Default(false);
 
   if (!supported) {
     DiagnosedSilenceableFailure diag =