[KernelGen] Lower tf.Erf and tf.Erfc ops to CHLO.

This does not include the lowerings from CHLO to LMHLO.

PiperOrigin-RevId: 344091604

include/mlir-hlo/Dialect/mhlo/IR/chlo_ops.td

@@ -417,6 +417,32 @@ def HLOClient_ConstantLikeOp : HLOClient_Op<"constant_like",
   let hasCanonicalizer = 1;
 }
 
+def HLOClient_ErfOp : HLOClient_UnaryElementwiseOp<"erf",
+    [NoSideEffect, SameOperandsAndResultShape],
+    HLO_FpTensor> {
+  let summary = "Erfc operator";
+
+  let description = [{
+    Computes the Gauss error function of `x` element-wise.
+
+    erf(x) = erf_impl(x)            if |x| < 1
+           = 1 - erfc_impl(x)       otherwise
+  }];
+}
+
+def HLOClient_ErfcOp : HLOClient_UnaryElementwiseOp<"erfc",
+    [NoSideEffect, SameOperandsAndResultShape],
+    HLO_FpTensor> {
+  let summary = "Erfc operator";
+
+  let description = [{
+    Computes an approximation of the error function complement (1 - erf(x)).
+
+    erfc(x) = erfc_impl(x)           if |x| > 1
+            = 1 - erf_impl(x)        otherwise
+  }];
+}
+
 //===----------------------------------------------------------------------===//
 // Broadcasting compare op
 //===----------------------------------------------------------------------===//

lib/Dialect/mhlo/transforms/transform_unranked_hlo.cc

@@ -50,7 +50,8 @@ namespace {
 
 // TODO(herhut): Generate these out of op definitions.
 #define MAP_CHLO_OPERATION_CWISE_UNARY(fn, sep)                         \
-  fn(AcosOp) sep fn(AtanOp) sep fn(SinhOp) sep fn(TanOp)
+  fn(AcosOp) sep fn(AtanOp) sep fn(ErfOp) sep fn(ErfcOp) sep fn(SinhOp) \
+      sep fn(TanOp)
 
 template <typename OpTy>
 inline void AddLegalOpOnRankedTensor(ConversionTarget *target) {