https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108318
Alexander Monakov <amonakov at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |amonakov at gcc dot gnu.org
--- Comment #1 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
Please see documentation for the -frounding-math option, but even with that
option added, your testcase still has the faux-invariant moved by RTL PRE
(-fno-gcse).
Interestingly, if your testcase is modified to compute the sum before the call:
#include <fenv.h>
void
foo (double res[4], double a, double b, double x[])
{
a = x[0];
b = x[1];
static const int rm[4]
= { FE_DOWNWARD, FE_TONEAREST, FE_TOWARDZERO, FE_UPWARD };
for (int i = 0; i < 4; ++i)
{
double t = a + b;
fesetround (rm[i]);
res[i] = t;
}
fesetround (FE_TONEAREST); // restore default
}
Then it demonstrates how a few *other* optimizations also perform unwanted
motion:
* SSA PRE (-fno-tree-pre)
* TER (-fno-tree-ter)
* RTL LIM (-fno-move-loop-invariants)
* and finally the register allocator (unavoidable)
