https://gcc.gnu.org/bugzilla/show_bug.cgi?id=34678
--- Comment #36 from Richard Biener <rguenth at gcc dot gnu.org> --- Created attachment 46396 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46396&action=edit poor mans solution^Whack So this is what a hack looks like, basically sprinkling those asm()s throughout the code automatically. Note I need to protect inputs, not outputs, otherwise the last testcase isn't fixed. Improving this poor-mans solution by writing in some flow-sensitivity like tracking which values are already protected and if there's a possibly harmful FENV access inbetween maybe in a similar way tree-complex.c tracks complex components might work. Note that the FENV pragma does _not_ enable -frounding-math (it really has no effect!) so you need to supply -frounding-math yourself (or fix the frontends to do that). It's a hack of course. But it fixes the testcase: > ./xgcc -B. t.c -O3 -lm > ./a.out 1/0.2: down = 4.999999999999999 near = 4.999999999999999 up = 4.999999999999999 a.out: t.c:32: main: Assertion `5.0 <= up' failed. Aborted > ./xgcc -B. t.c -O3 -lm -frounding-math > ./a.out 1/0.2: down = 4.999999999999999 near = 5 up = 5 IL after the lowering: main () { static const char __PRETTY_FUNCTION__[5] = "main"; double near; double up; double down; double op; int D.3058; op = atof ("0.2"); fesetround (1024); __asm__ __volatile__("" : "=g" op : "0" op); down = 1.0e+0 / op; fesetround (2048); __asm__ __volatile__("" : "=g" op : "0" op); up = 1.0e+0 / op; fesetround (0); __asm__ __volatile__("" : "=g" op : "0" op); near = 1.0e+0 / op; printf ("1/%.16g: down = %.16g near = %.16g up = %.16g\n", op, down, near, up); ...
