[mlir][complex] Fastmath flag for complex angle (#88658)

See
https://discourse.llvm.org/t/rfc-fastmath-flags-support-in-complex-dialect/71981

Author: Lewuathe

mlir/lib/Conversion/ComplexToStandard/ComplexToStandard.cpp

@@ -1289,13 +1289,14 @@ struct AngleOpConversion : public OpConversionPattern<complex::AngleOp> {
                   ConversionPatternRewriter &rewriter) const override {
     auto loc = op.getLoc();
     auto type = op.getType();
+    arith::FastMathFlagsAttr fmf = op.getFastMathFlagsAttr();
 
     Value real =
         rewriter.create<complex::ReOp>(loc, type, adaptor.getComplex());
     Value imag =
         rewriter.create<complex::ImOp>(loc, type, adaptor.getComplex());
 
-    rewriter.replaceOpWithNewOp<math::Atan2Op>(op, imag, real);
+    rewriter.replaceOpWithNewOp<math::Atan2Op>(op, imag, real, fmf);
 
     return success();
   }

mlir/test/Conversion/ComplexToStandard/convert-to-standard.mlir

@@ -2187,3 +2187,16 @@ func.func @complex_tanh_nnan_ninf(%arg: complex<f32>) -> complex<f32> {
 
 // CHECK-COUNT-1: arith.select
 // CHECK-NOT: arith.select
+
+// -----
+
+// CHECK-LABEL:   func.func @complex_angle_with_fmf
+// CHECK-SAME: %[[ARG:.*]]: complex<f32>
+func.func @complex_angle_with_fmf(%arg: complex<f32>) -> f32 {
+  %angle = complex.angle %arg fastmath<nnan,contract> : complex<f32>
+  return %angle : f32
+}
+// CHECK: %[[REAL:.*]] = complex.re %[[ARG]] : complex<f32>
+// CHECK: %[[IMAG:.*]] = complex.im %[[ARG]] : complex<f32>
+// CHECK: %[[RESULT:.*]] = math.atan2 %[[IMAG]], %[[REAL]] fastmath<nnan,contract> : f32
+// CHECK: return %[[RESULT]] : f32