[mlir][Math] Add constant folder for RoundOp.

[jacquesguan]

Summary

This patch uses round/roundf of libm to fold RoundOp of constant.

[Mogball]

can you check the windows build? Or did you need to rebase this patch

[jacquesguan]

rebase main

[jacquesguan]

In D133401#3774716, @Mogball wrote:

can you check the windows build? Or did you need to rebase this patch

Done.

mlir/include/mlir/Dialect/Math/IR/MathOps.td

let description = [{
 
     Example:
 
     ```mlir
     // Scalar round operation.
     %a = math.round %b : f64
     ```
   }];
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//
 // FPowIOp
 //===----------------------------------------------------------------------===//
 
 def Math_FPowIOp : Math_Op<"fpowi",
     [SameOperandsAndResultShape, AllTypesMatch<["lhs", "result"]>]> {

mlir/lib/Dialect/Math/IR/MathOps.cpp

 OpFoldResult math::RoundEvenOp::fold(ArrayRef<Attribute> operands) {
   return constFoldUnaryOp<FloatAttr>(operands, [](const APFloat &a) {
     APFloat result(a);
     result.roundToIntegral(llvm::RoundingMode::NearestTiesToEven);
     return result;
   });
 }
 
+//===----------------------------------------------------------------------===//
+// RoundOp folder
+//===----------------------------------------------------------------------===//
+
+OpFoldResult math::RoundOp::fold(ArrayRef<Attribute> operands) {
+  return constFoldUnaryOpConditional<FloatAttr>(
+      operands, [](const APFloat &a) -> Optional<APFloat> {
+        switch (a.getSizeInBits(a.getSemantics())) {
+        case 64:
+          return APFloat(round(a.convertToDouble()));
+        case 32:
+          return APFloat(roundf(a.convertToFloat()));
+        default:
+          return {};
+        }
+      });
+}
+
 /// Materialize an integer or floating point constant.
 Operation *math::MathDialect::materializeConstant(OpBuilder &builder,
                                                   Attribute value, Type type,
                                                   Location loc) {
   return builder.create<arith::ConstantOp>(loc, value, type);
 }

mlir/test/Dialect/Math/canonicalize.mlir

 // CHECK-LABEL: @roundeven_fold_vec
 // CHECK-NEXT: %[[cst:.+]] = arith.constant dense<[0.000000e+00, -0.000000e+00, 2.000000e+00, -2.000000e+00]> : vector<4xf32>
 // CHECK-NEXT:   return %[[cst]]
 func.func @roundeven_fold_vec() -> (vector<4xf32>) {
   %v1 = arith.constant dense<[0.5, -0.5, 1.5, -1.5]> : vector<4xf32>
   %0 = math.roundeven %v1 : vector<4xf32>
   return %0 : vector<4xf32>
 }
+
+// CHECK-LABEL: @round_fold
+// CHECK-NEXT: %[[cst:.+]] = arith.constant 2.000000e+00 : f32
+// CHECK-NEXT:   return %[[cst]]
+func.func @round_fold() -> f32 {
+  %c = arith.constant 1.5 : f32
+  %r = math.round %c : f32
+  return %r : f32
+}
+
+// CHECK-LABEL: @round_fold_vec
+// CHECK-NEXT: %[[cst:.+]] = arith.constant dense<[1.000000e+00, -1.000000e+00, 2.000000e+00, -2.000000e+00]> : vector<4xf32>
+// CHECK-NEXT:   return %[[cst]]
+func.func @round_fold_vec() -> (vector<4xf32>) {
+  %v1 = arith.constant dense<[0.5, -0.5, 1.5, -1.5]> : vector<4xf32>
+  %0 = math.round %v1 : vector<4xf32>
+  return %0 : vector<4xf32>
+}