float_t supposedly represents the type that is used to evaluate float expressions internally. While the isa supports single-precision float operations, the port of glibc to s390 incorrectly deferred to the generic definitions which, back then, tied float_t to double. gcc by default evaluates float in single precision, so that scenario violates the C standard (sections 220.127.116.11.2 and 7.12 in C11/C17). With-fexcess-precision=standard, gcc evaluates float in double precision, which aligns with the standard yet at the cost of added conversion instructions.
With this patch, we drop the s390-specific definition of float_t and defer to the default behavior, which aligns float_t with the compiler-defined FLT_EVAL_METHOD in a standard-compliant way.
Checked on s390x-linux-gnu with 31-bit and 64-bit builds.
f88242af19 S390: Derive float_t from FLT_EVAL_METHOD
NEWS | 7 +++++++
sysdeps/s390/bits/flt-eval-method.h | 24 ------------------------
2 files changed, 7 insertions(+), 24 deletions(-)