[mlir][Math] Add constant folder for Atan2Op.

This patch adds constant folder for Atan2Op which only supports single and double precision floating-point.

Differential Revision: https://reviews.llvm.org/D131050

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

@@ -144,6 +144,7 @@ def Math_Atan2Op : Math_FloatBinaryOp<"atan2">{
     %a = math.atan2 %b, %c : f32
     ```
   }];
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//

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

@@ -50,6 +50,28 @@ OpFoldResult math::AtanOp::fold(ArrayRef<Attribute> operands) {
       });
 }
 
+//===----------------------------------------------------------------------===//
+// Atan2Op folder
+//===----------------------------------------------------------------------===//
+
+OpFoldResult math::Atan2Op::fold(ArrayRef<Attribute> operands) {
+  return constFoldBinaryOpConditional<FloatAttr>(
+      operands, [](const APFloat &a, const APFloat &b) -> Optional<APFloat> {
+        if (a.isZero() && b.isZero())
+          return llvm::APFloat::getNaN(a.getSemantics());
+
+        if (a.getSizeInBits(a.getSemantics()) == 64 &&
+            b.getSizeInBits(b.getSemantics()) == 64)
+          return APFloat(atan2(a.convertToDouble(), b.convertToDouble()));
+
+        if (a.getSizeInBits(a.getSemantics()) == 32 &&
+            b.getSizeInBits(b.getSemantics()) == 32)
+          return APFloat(atan2f(a.convertToFloat(), b.convertToFloat()));
+
+        return {};
+      });
+}
+
 //===----------------------------------------------------------------------===//
 // CeilOp folder
 //===----------------------------------------------------------------------===//

mlir/test/Dialect/Math/canonicalize.mlir

@@ -337,3 +337,24 @@ func.func @atan_fold_vec() -> (vector<4xf32>) {
   %0 = math.atan %v1 : vector<4xf32>
   return %0 : vector<4xf32>
 }
+
+// CHECK-LABEL: @atan2_fold
+// CHECK-NEXT: %[[cst:.+]] = arith.constant 0.000000e+00 : f32
+// CHECK-NEXT:   return %[[cst]]
+func.func @atan2_fold() -> f32 {
+  %c1 = arith.constant 0.0 : f32
+  %c2 = arith.constant 1.0 : f32
+  %r = math.atan2 %c1, %c2 : f32
+  return %r : f32
+}
+
+// CHECK-LABEL: @atan2_fold_vec
+// CHECK-NEXT: %[[cst:.+]] = arith.constant dense<[0.000000e+00, 0.000000e+00, 0.463647604, 0.463647604]> : vector<4xf32>
+// CHECK-NEXT:   return %[[cst]]
+func.func @atan2_fold_vec() -> (vector<4xf32>) {
+  %v1 = arith.constant dense<[0.0, 0.0, 1.0, 1.0]> : vector<4xf32>
+  %v2 = arith.constant dense<[1.0, 1.0, 2.0, 2.0]> : vector<4xf32>
+  %0 = math.atan2 %v1, %v2 : vector<4xf32>
+  return %0 : vector<4xf32>
+}
+

mlir/test/mlir-cpu-runner/math-polynomial-approx.mlir

@@ -474,7 +474,7 @@ func.func @atan2() {
   %atan2_8 = math.atan2 %neg_two, %one : f32
   vector.print %atan2_8 : f32
 
-  // CHECK: 0.463643
+  // CHECK: 0.463648
   %atan2_9 = math.atan2 %one, %two : f32
   vector.print %atan2_9 : f32
 
@@ -490,7 +490,7 @@ func.func @atan2() {
   %atan2_11 = math.atan2 %neg_one, %neg_two : f32
   vector.print %atan2_11 : f32
 
-  // CHECK: -0.463643
+  // CHECK: -0.463648
   %atan2_12 = math.atan2 %neg_one, %two : f32
   vector.print %atan2_12 : f32