------- Comment #2 from piotr dot wyderski at gmail dot com 2010-03-31 11:00
-------
With -ffast-math the code becomes
.file "testcase.cpp"
.text
.p2align 4,,15
.globl __Z3fn1d
.def __Z3fn1d; .scl 2; .type 32; .endef
__Z3fn1d:
fldl 4(%esp)
fsincos
fmulp %st, %st(1)
ret
.p2align 4,,15
.globl __Z3fn2d
.def __Z3fn2d; .scl 2; .type 32; .endef
__Z3fn2d:
fldl 4(%esp)
fsincos
fmulp %st, %st(1)
ret
which is exactly the expected output, but:
-ffast-math: This option should never be turned
on by any -O option since it can result in
incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications
for math functions.
So, what IEEE rules does the fsin/fcos/fsincos
emission/fussion break? The only problem I see
is excessive accuracy, but it can be removed using
the fld/fst trick used by -ffloat-store (and THAT
can be removed by -ffast-math), without the need
to declare the entire program as IEEE754 non-conformant.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43599
