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[flang] Optimize acospi precision #152869

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Merged
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Aug 11, 2025
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[flang] Optimize acospi precision #152869

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8 changes: 4 additions & 4 deletions flang/lib/Optimizer/Builder/IntrinsicCall.cpp
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Expand Up @@ -2687,10 +2687,10 @@ mlir::Value IntrinsicLibrary::genAcospi(mlir::Type resultType,
mlir::FunctionType ftype =
mlir::FunctionType::get(context, {resultType}, {args[0].getType()});
mlir::Value acos = getRuntimeCallGenerator("acos", 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, acos, factor);
}

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14 changes: 12 additions & 2 deletions flang/test/Lower/Intrinsics/acospi.f90
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@@ -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"
Expand All @@ -10,8 +11,7 @@ function test_real4(x)
! CHECK-LABEL: @_QPtest_real4
! CHECK-PRECISE: %[[acos:.*]] = fir.call @acosf({{%[A-Za-z0-9._]+}}) fastmath<contract> : (f32) -> f32
! CHECK-FAST: %[[acos:.*]] = math.acos %{{.*}} : 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 %[[acos]], %[[inv_pi]] fastmath<contract> : f32

function test_real8(x)
Expand All @@ -24,3 +24,13 @@ function test_real8(x)
! CHECK-FAST: %[[acos:.*]] = math.acos %{{.*}} : f64
! CHECK: %[[inv_pi:.*]] = arith.constant 0.31830988618379069 : f64
! CHECK: %{{.*}} = arith.mulf %[[acos]], %[[inv_pi]] fastmath<contract> : f64

function test_real16(x)
real(16) :: x, test_real16
test_real16 = acospi(x)
end function

! CHECK-LABEL: @_QPtest_real16
! CHECK: %[[acos:.*]] = fir.call @_FortranAAcosF128({{.*}}) fastmath<contract> : (f128) -> f128
! CHECK: %[[inv_pi:.*]] = arith.constant 0.3183098861837906715377675267450{{.*}} : f128
! CHECK: %{{.*}} = arith.mulf %[[acos]], %[[inv_pi]] fastmath<contract> : f128
4 changes: 4 additions & 0 deletions llvm/include/llvm/Support/MathExtras.h
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Expand Up @@ -74,6 +74,10 @@ constexpr float ef = 0x1.5bf0a8P+1F, // (2.71828183) https://oeis.org/A
sqrt3f = 0x1.bb67aeP+0F, // (1.73205081) https://oeis.org/A002194
inv_sqrt3f = 0x1.279a74P-1F, // (.577350269)
phif = 0x1.9e377aP+0F; // (1.61803399) https://oeis.org/A001622
// These string literals are taken from below:
// https://github.com/bminor/glibc/blob/8543577b04ded6d979ffcc5a818930e4d74d0645/math/math.h#L1215-L1229
constexpr const char *pis = "3.141592653589793238462643383279502884",
*inv_pis = "0.318309886183790671537767526745028724";
// clang-format on
} // namespace numbers

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