[glibc/azanella/clang] math: Fix potential underflow on ldbl-128 erfl

[Adhemerval Zanella <azanella@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=3199b1cc5b9f2ca0714b803b66f4a24e0fa2aa21

commit 3199b1cc5b9f2ca0714b803b66f4a24e0fa2aa21
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Tue Jan 30 13:45:14 2024 +0000

    math: Fix potential underflow on ldbl-128 erfl
    
    The multiplication is only required if the branch is taken, and the
    compiler might not optimize it away.
    
    Checked on aarch64-linux-gnu with gcc and clang.

Diff:
---
 sysdeps/ieee754/ldbl-128/s_erfl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sysdeps/ieee754/ldbl-128/s_erfl.c b/sysdeps/ieee754/ldbl-128/s_erfl.c
index 1cbedc249d..e52d88bde3 100644
--- a/sysdeps/ieee754/ldbl-128/s_erfl.c
+++ b/sysdeps/ieee754/ldbl-128/s_erfl.c
@@ -778,7 +778,6 @@ __erfl (_Float128 x)
     }
   u.parts32.w0 = ix;
   a = u.value;
-  z = x * x;
   if (ix < 0x3ffec000)  /* a < 0.875 */
     {
       if (ix < 0x3fc60000) /* |x|<2**-57 */
@@ -792,6 +791,7 @@ __erfl (_Float128 x)
 	    }
 	  return x + efx * x;
 	}
+      z = x * x;
       y = a + a * neval (z, TN1, NTN1) / deval (z, TD1, NTD1);
     }
   else