[flang-commits] [flang] [flang] optimize `tand` precision (PR #155629)

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https://github.com/c8ef created https://github.com/llvm/llvm-project/pull/155629

Closes #150452.

>From d31c9a34c50612480249e4eba524bff4466543ca Mon Sep 17 00:00:00 2001
From: c8ef <c8ef at outlook.com>
Date: Wed, 27 Aug 2025 22:27:08 +0800
Subject: [PATCH] [flang] optimize tand precision

---
 flang/lib/Optimizer/Builder/IntrinsicCall.cpp |  9 +++++----
 flang/test/Lower/Intrinsics/tand.f90          | 14 ++++++++++++--
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/flang/lib/Optimizer/Builder/IntrinsicCall.cpp b/flang/lib/Optimizer/Builder/IntrinsicCall.cpp
index f6d71a9d1d933..70a3734798379 100644
--- a/flang/lib/Optimizer/Builder/IntrinsicCall.cpp
+++ b/flang/lib/Optimizer/Builder/IntrinsicCall.cpp
@@ -8290,10 +8290,11 @@ mlir::Value IntrinsicLibrary::genTand(mlir::Type resultType,
   mlir::MLIRContext *context = builder.getContext();
   mlir::FunctionType ftype =
       mlir::FunctionType::get(context, {resultType}, {args[0].getType()});
-  llvm::APFloat pi = llvm::APFloat(llvm::numbers::pi);
-  mlir::Value dfactor = builder.createRealConstant(
-      loc, mlir::Float64Type::get(context), pi / llvm::APFloat(180.0));
-  mlir::Value factor = builder.createConvert(loc, args[0].getType(), dfactor);
+  const llvm::fltSemantics &fltSem =
+      llvm::cast<mlir::FloatType>(resultType).getFloatSemantics();
+  llvm::APFloat pi = llvm::APFloat(fltSem, llvm::numbers::pis);
+  mlir::Value factor = builder.createRealConstant(
+      loc, resultType, pi / llvm::APFloat(fltSem, "180.0"));
   mlir::Value arg = mlir::arith::MulFOp::create(builder, loc, args[0], factor);
   return getRuntimeCallGenerator("tan", ftype)(builder, loc, {arg});
 }
diff --git a/flang/test/Lower/Intrinsics/tand.f90 b/flang/test/Lower/Intrinsics/tand.f90
index b0f0c52400f78..8c8927e6f5a99 100644
--- a/flang/test/Lower/Intrinsics/tand.f90
+++ b/flang/test/Lower/Intrinsics/tand.f90
@@ -1,3 +1,4 @@
+! REQUIRES: flang-supports-f128-math
 ! RUN: bbc -emit-fir %s -o - | FileCheck %s --check-prefixes="CHECK,CHECK-FAST"
 ! RUN: bbc --math-runtime=precise -emit-fir %s -o - | FileCheck %s --check-prefixes="CHECK,CHECK-PRECISE"
 ! RUN: %flang_fc1 -emit-fir %s -o - | FileCheck %s --check-prefixes="CHECK,CHECK-FAST"
@@ -8,8 +9,7 @@ function test_real4(x)
 end function
 
 ! CHECK-LABEL: @_QPtest_real4
-! CHECK: %[[dfactor:.*]] = arith.constant 0.017453292519943295 : f64
-! CHECK: %[[factor:.*]] = fir.convert %[[dfactor]] : (f64) -> f32
+! CHECK: %[[factor:.*]] = arith.constant 0.0174532924 : f32
 ! CHECK: %[[arg:.*]] = arith.mulf %{{[A-Za-z0-9._]+}}, %[[factor]] fastmath<contract> : f32
 ! CHECK-PRECISE: %{{.*}} = fir.call @tanf(%[[arg]]) fastmath<contract> : (f32) -> f32
 ! CHECK-FAST: %{{.*}} = math.tan %[[arg]] fastmath<contract> : f32
@@ -24,3 +24,13 @@ function test_real8(x)
 ! CHECK: %[[arg:.*]] = arith.mulf %{{[A-Za-z0-9._]+}}, %[[factor]] fastmath<contract> : f64
 ! CHECK-PRECISE: %{{.*}} = fir.call @tan(%[[arg]]) fastmath<contract> : (f64) -> f64
 ! CHECK-FAST: %{{.*}} = math.tan %[[arg]] fastmath<contract> : f64
+
+function test_real16(x)
+  real(16) :: x, test_real16
+  test_real16 = tand(x)
+end function
+
+! CHECK-LABEL: @_QPtest_real16
+! CHECK: %[[factor:.*]] = arith.constant 0.0174532925199432957692369076848861{{.*}} : f128
+! CHECK: %[[arg:.*]] = arith.mulf %{{[A-Za-z0-9._]+}}, %[[factor]] fastmath<contract> : f128
+! CHECK: %[[result:.*]] = fir.call @_FortranATanF128({{.*}}) fastmath<contract> : (f128) -> f128