[PATCH] math: Improve layout of exp/exp10 data

[Wilco Dijkstra]

GCC aligns global data to 16 bytes if their size is >= 16 bytes.  This patch
changes the exp_data struct slightly so that the fields are better aligned
and without gaps.  As a result on targets that support them, more load-pair
instructions are used in exp.  Exp10 is improved by moving invlog10_2N later
so that neglog10_2hiN and neglog10_2loN can be loaded using load-pair.

The exp benchmark improves 2.5%, "144bits" by 7.2%, "768bits" by 12.7% on
Neoverse V2.  Exp10 improves by 1.5%.

Passes regress, OK for commit?

---

diff --git a/sysdeps/ieee754/dbl-64/math_config.h b/sysdeps/ieee754/dbl-64/math_config.h
index ef87cfa6be9860e3c11d44585bda02612369fa6d..05515fd95ad15d52499860539f7a1c20f4bca248 100644
--- a/sysdeps/ieee754/dbl-64/math_config.h
+++ b/sysdeps/ieee754/dbl-64/math_config.h
@@ -195,16 +195,18 @@ check_uflow (double x)
 extern const struct exp_data
 {
   double invln2N;
-  double shift;
   double negln2hiN;
   double negln2loN;
   double poly[4]; /* Last four coefficients.  */
+  double shift;
+
   double exp2_shift;
   double exp2_poly[EXP2_POLY_ORDER];
-  double invlog10_2N;
+
   double neglog10_2hiN;
   double neglog10_2loN;
   double exp10_poly[5];
+  double invlog10_2N;
   uint64_t tab[2*(1 << EXP_TABLE_BITS)];
 } __exp_data attribute_hidden;