[flang] Optimize asinpi precision (#153203)

Part of #150452.

Author: c8ef

flang/lib/Optimizer/Builder/IntrinsicCall.cpp

@@ -2855,10 +2855,10 @@ mlir::Value IntrinsicLibrary::genAsinpi(mlir::Type resultType,
   mlir::FunctionType ftype =
       mlir::FunctionType::get(context, {resultType}, {args[0].getType()});
   mlir::Value asin = getRuntimeCallGenerator("asin", ftype)(builder, loc, args);
-  llvm::APFloat inv_pi = llvm::APFloat(llvm::numbers::inv_pi);
-  mlir::Value dfactor =
-      builder.createRealConstant(loc, mlir::Float64Type::get(context), inv_pi);
-  mlir::Value factor = builder.createConvert(loc, resultType, dfactor);
+  llvm::APFloat inv_pi =
+      llvm::APFloat(llvm::cast<mlir::FloatType>(resultType).getFloatSemantics(),
+                    llvm::numbers::inv_pis);
+  mlir::Value factor = builder.createRealConstant(loc, resultType, inv_pi);
   return mlir::arith::MulFOp::create(builder, loc, asin, factor);
 }
 

flang/test/Lower/Intrinsics/asinpi.f90

@@ -1,3 +1,4 @@
+! REQUIRES: flang-supports-f128-math
 ! RUN: bbc -emit-fir -hlfir=false %s -o - | FileCheck %s --check-prefixes="CHECK,CHECK-FAST"
 ! RUN: bbc --math-runtime=precise -emit-fir -hlfir=false %s -o - | FileCheck %s --check-prefixes="CHECK,CHECK-PRECISE"
 ! RUN: %flang_fc1 -emit-fir -flang-deprecated-no-hlfir %s -o - | FileCheck %s --check-prefixes="CHECK,CHECK-FAST"
@@ -10,8 +11,7 @@ function test_real4(x)
 ! CHECK-LABEL: @_QPtest_real4
 ! CHECK-PRECISE: %[[asin:.*]] = fir.call @asinf({{%[A-Za-z0-9._]+}}) fastmath<contract> : (f32) -> f32
 ! CHECK-FAST: %[[asin:.*]] = math.asin %{{.*}} : f32
-! CHECK: %[[dpi:.*]] = arith.constant 0.31830988618379069 : f64
-! CHECK: %[[inv_pi:.*]] = fir.convert %[[dpi]] : (f64) -> f32
+! CHECK: %[[inv_pi:.*]] = arith.constant 0.318309873 : f32
 ! CHECK: %{{.*}} = arith.mulf %[[asin]], %[[inv_pi]] fastmath<contract> : f32
 
 function test_real8(x)
@@ -24,3 +24,13 @@ function test_real8(x)
 ! CHECK-FAST: %[[asin:.*]] = math.asin %{{.*}} : f64
 ! CHECK: %[[inv_pi:.*]] = arith.constant 0.31830988618379069 : f64
 ! CHECK: %{{.*}} = arith.mulf %[[asin]], %[[inv_pi]] fastmath<contract> : f64
+
+function test_real16(x)
+  real(16) :: x, test_real16
+  test_real16 = asinpi(x)
+end function
+
+! CHECK-LABEL: @_QPtest_real16
+! CHECK: %[[asin:.*]] = fir.call @_FortranAAsinF128({{.*}}) fastmath<contract> : (f128) -> f128
+! CHECK: %[[inv_pi:.*]] = arith.constant 0.3183098861837906715377675267450{{.*}} : f128
+! CHECK: %{{.*}} = arith.mulf %[[asin]], %[[inv_pi]] fastmath<contract> : f128