This change enables the "t1 != 0" check to be optimized away in this code:
int x1 = 0;
unsigned int x2 = 1;
int main ()
{
int t1 = x1*(1/(x2+x2));
if (t1 != 0) __builtin_abort();
return 0;
}
The change utilizes the VRP framework to propagate the get_nonzero_bits
information from the "x2+x2" expression to the "1/(x2+x2)" division expression.
Specifically, the framework knows that the least significant bit of the "x2+x2"
expression must be zero.
The get_nonzero_bits information of the left hand side and right hand side of
expressions needed to be passed down to operator_div::wi_fold() in the VRP
framework. The majority of this change involves adding two additional
parameters to propagate this information. There are future opportunities to use
the non zero bit information to perform better optimizations in other types of
expressions.
The changes were tested against x86_64-pc-linux-gnu and all tests in "make -k
check" passed.
The original approach was to implement a match.pd pattern to support this but
the pattern wasn't being triggered. More context is available in:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77980
Thanks,
Victor
pr77980.patch
Description: pr77980.patch
