On 8/18/2026 12:26 PM, Sam James wrote:
Jeffrey Law <[email protected]> writes:
On 8/14/2026 1:29 PM, Matt Turner wrote:
Alpha encodes the rounding mode in the instruction itself, so honoring a
rounding mode chosen at run time requires the /d qualifier, which takes the
mode from the FPCR. alpha_fprm defaulted to ALPHA_FPRM_NORM and was only
ever changed by an explicit -mfp-rounding-mode, so -frounding-math emitted
statically rounded instructions and fesetround was silently ignored.
Default alpha_fprm to ALPHA_FPRM_DYN when -frounding-math is in effect and
-mfp-rounding-mode was not given, leaving both ordinary code generation and
an explicit -mfp-rounding-mode unaffected. The VAX floating-point
instructions have no dynamic rounding qualifier, so -mfloat-vax keeps the
static default.
This fixes the execution failures of
gcc.dg/torture/fp-uint64-convert-double-1.c,
fp-uint64-convert-double-2.c and fp-double-convert-float-1.c.
gcc/ChangeLog:
* config/alpha/alpha.cc (alpha_option_override): Set alpha_fprm to
ALPHA_FPRM_DYN when flag_rounding_math is set, -mfp-rounding-mode
was not given explicitly and -mfloat-vax is not in effect.
* doc/invoke.texi (Alpha Options): Document the default rounding
mode and its interaction with -frounding-math.
THanks. I've pushed this to the trunk as well. My last alpha build
didn't bootstrap, so something has gone weird, but I suspect it's
generic and not anything you've done.
The last clean build I had was with:
7e0bb48cbb2654816ce2714de5b644f4d965d3db
The first failed build with:
df494ca28d75f80b4d0b4e0b93b5d23d2092131a
The failure mode is an ICE in the gimple threader:
during GIMPLE pass: thread
../../../gcc/libcpp/lex.cc: In function 'void _cpp_clean_line(cpp_reader*)':
../../../gcc/libcpp/lex.cc:970:1: internal compiler error: Segmentation fault
970 | _cpp_clean_line (cpp_reader *pfile)
| ^~~~~~~~~~~~~~~
I haven't tried to chase it down yet. I usually let these things
simmer a bit since testing/bisecting bootstraps of qemu emulated
targets takes an absurdly long time. But if you're interested in
chasing another issue, this may be good to check.
It's https://gcc.gnu.org/PR126876 which Aldy just fixed but trunk is
kind of rough at the moment, there's https://gcc.gnu.org/PR126856 too.
ACK. Thanks for the update. I've been effectively offline the last
several days, but I do see that alpha's run yesterday was successful, so
hopefully the inability is easing.
jeff
