[PATCH v2 4/5] math: Use math_opt_barrier on ldbl-128 powl underflow/overflow handling

[Adhemerval Zanella]

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
---
 sysdeps/ieee754/ldbl-128/e_powl.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/sysdeps/ieee754/ldbl-128/e_powl.c b/sysdeps/ieee754/ldbl-128/e_powl.c
index 4e20616705..9ff5a43573 100644
--- a/sysdeps/ieee754/ldbl-128/e_powl.c
+++ b/sysdeps/ieee754/ldbl-128/e_powl.c
@@ -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)
-- 
2.43.0