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

Differential Revision: https://reviews.llvm.org/D121980

Author: jacquesguan

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

@@ -724,6 +724,7 @@ def Math_SqrtOp : Math_FloatUnaryOp<"sqrt"> {
     %x = math.sqrt %y : tensor<4x?xf32>
     ```
   }];
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//

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

@@ -101,6 +101,31 @@ OpFoldResult math::PowFOp::fold(ArrayRef<Attribute> operands) {
   return {};
 }
 
+OpFoldResult math::SqrtOp::fold(ArrayRef<Attribute> operands) {
+  auto constOperand = operands.front();
+  if (!constOperand)
+    return {};
+
+  auto attr = constOperand.dyn_cast<FloatAttr>();
+  if (!attr)
+    return {};
+
+  auto ft = getType().cast<FloatType>();
+
+  APFloat apf = attr.getValue();
+
+  if (apf.isNegative())
+    return {};
+
+  if (ft.getWidth() == 64)
+    return FloatAttr::get(getType(), sqrt(apf.convertToDouble()));
+
+  if (ft.getWidth() == 32)
+    return FloatAttr::get(getType(), sqrtf(apf.convertToFloat()));
+
+  return {};
+}
+
 /// Materialize an integer or floating point constant.
 Operation *math::MathDialect::materializeConstant(OpBuilder &builder,
                                                   Attribute value, Type type,

mlir/test/Dialect/Math/canonicalize.mlir

@@ -82,3 +82,12 @@ func @powf_fold() -> f32 {
   %r = math.powf %c, %c : f32
   return %r : f32
 }
+
+// CHECK-LABEL: @sqrt_fold
+// CHECK: %[[cst:.+]] = arith.constant 2.000000e+00 : f32
+// CHECK: return %[[cst]]
+func @sqrt_fold() -> f32 {
+  %c = arith.constant 4.0 : f32
+  %r = math.sqrt %c : f32
+  return %r : f32
+}