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math: Use math_opt_barrier on ldbl-128 powl underflow/overflow handling 

This avoids compiler to move the operation before the 'iy' compare.

It fixes math/test-float128-pow regreesions when building with clang [1]:

Failure: pow (-0x1.000002p+0, 0xf.ffffffffffff8p+1020): Exception "Underflow" set
Failure: pow (-0x1.000002p+0, 0xf.ffffffffffffbffffffffffffcp+1020): Exception "Underflow" set
Failure: pow (-0x1.000002p+0, 0xf.fffffffffffffffffffffffffff8p+16380): Exception "Underflow" set
Failure: pow (-0x1.000002p+0, 0xf.fffffffffffffffp+16380): Exception "Underflow" set
Failure: pow (-0x1.000002p+0, 0xf.fffffp+124): Exception "Underflow" set
Failure: pow (-0x1.00000ep+0, 0xf.ffffffffffff8p+1020): Exception "Underflow" set
Failure: pow (-0x1.00000ep+0, 0xf.ffffffffffffbffffffffffffcp+1020): Exception "Underflow" set
Failure: pow (-0x1.00000ep+0, 0xf.fffffffffffffffffffffffffff8p+16380): Exception "Underflow" set
Failure: pow (-0x1.00000ep+0, 0xf.fffffffffffffffp+16380): Exception "Underflow" set
Failure: pow (-0x2p+0, -0xf.ffffffffffff8p+1020): Exception "Overflow" set
Failure: pow (-0x2p+0, -0xf.ffffffffffffbffffffffffffcp+1020): Exception "Overflow" set
Failure: pow (-0x2p+0, -0xf.fffffffffffffffffffffffffff8p+16380): Exception "Overflow" set
Failure: pow (-0x2p+0, -0xf.fffffffffffffffp+16380): Exception "Overflow" set
Failure: pow (-0x2p+0, -0xf.fffffp+124): Exception "Overflow" set
Failure: pow (-0x2p+0, 0xf.ffffffffffff8p+1020): Exception "Underflow" set
Failure: pow (-0x2p+0, 0xf.ffffffffffffbffffffffffffcp+1020): Exception "Underflow" set
Failure: pow (-0x2p+0, 0xf.fffffffffffffffffffffffffff8p+16380): Exception "Underflow" set
Failure: pow (-0x2p+0, 0xf.fffffffffffffffp+16380): Exception "Underflow" set
Failure: pow (-0x2p+0, 0xf.fffffp+124): Exception "Underflow" set
[...]

Checked on x86_64-linux-gnu and aarch64-linux-gnu with gcc-15 and
clang-18.

[1] https://github.com/llvm/llvm-project/issues/173080

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
This commit is contained in:
Adhemerval Zanella 2025-12-19 15:52:23 -03:00
parent bc78f67ca1
commit 7be72e37e6
1 changed files with 4 additions and 2 deletions
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6
sysdeps/ieee754/ldbl-128/e_powl.c
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@ -279,9 +279,11 @@ __ieee754_powl (_Float128 x, _Float128 y)
if (iy > 0x407d654b)
{
if (ix <= 0x3ffeffff)
return (hy < 0) ? huge * huge : tiny * tiny;
return (hy < 0) ? math_opt_barrier (huge * huge)
: math_opt_barrier (tiny * tiny);
if (ix >= 0x3fff0000)
return (hy > 0) ? huge * huge : tiny * tiny;
return (hy > 0) ? math_opt_barrier (huge * huge)
: math_opt_barrier (tiny * tiny);
}
/* over/underflow if x is not close to one */
if (ix < 0x3ffeffff)