[Bug target/46091] New: missed optimization: x86 bt/btc/bts instructions

[jay.krell at cornell dot edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46091

           Summary: missed optimization: x86 bt/btc/bts instructions
           Product: gcc
           Version: 4.3.5
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: jay.kr...@cornell.edu


The following code, at least when optimizing for space, should use x86
bt/btc/bts instructions.

#include <limits.h>
#include <stddef.h>

void set_bit(size_t* a, size_t b)
{
  const unsigned c = sizeof(size_t) * CHAR_BIT;
  a[b / c] |= (((size_t)1) << (b % c));
}

void clear_bit(size_t* a, size_t b)
{
  const unsigned c = sizeof(size_t) * CHAR_BIT;
  a[b / c] &=  ~(((size_t)1) << (b % c));
}

int get_bit(size_t* a, size_t b)
{
  const unsigned c = sizeof(size_t) * CHAR_BIT;
  return !!(a[b / c] & (((size_t)1) << (b % c)));
}