kmp_affinity: Fix check if specific bit is set

[Hahnfeld]

Summary

Clang 4.0 trunk warns:

warning: logical not is only applied to the left hand side of this bitwise operator [-Wlogical-not-parentheses]

This points to a potential bug if the code really wants to check if the single bit is not set: If for example (buf.edx >> 9) = 2 (has any bit set except the
least significant one), 'logical not' will return 0 which stays 0 after the 'bitwise and'.
To do this correctly we first need to evaluate the 'bitwise and'. In that case it returns 2 & 1 = 0 which after the 'logical not' evaluates to 1.

[jcownie]

Good point. My personal preference would be to use "== 0", rather than logical not, since I find that easier to read.
So

if (((buf.edx >> 9) & 1) == 0) {
    ...
}

But your fix is fine too.

[Hahnfeld]

In D28599#643871, @jcownie wrote:

Good point. My personal preference would be to use "== 0", rather than logical not, since I find that easier to read.
So

if (((buf.edx >> 9) & 1) == 0) {
    ...
}

But your fix is fine too.

I agree, that looks easier to read. Will do the change on commit once approved.

[AndreyChurbanov]

LGTM, either yours or Jim's suggestion.
Thanks.

runtime/src/kmp_affinity.cpp

KMP_CPU_SET_ITERATE(i, __kmp_affin_fullMask) {
 
         __kmp_affinity_dispatch->bind_thread(i);
         threadInfo[nApics].osId = i;
 
         //
         // The apic id and max threads per pkg come from cpuid(1).
         //
         __kmp_x86_cpuid(1, 0, &buf);
-        if (! (buf.edx >> 9) & 1) {
+        if (! ((buf.edx >> 9) & 1)) {
             __kmp_set_system_affinity(oldMask, TRUE);
             __kmp_free(threadInfo);
             KMP_CPU_FREE(oldMask);
             *msg_id = kmp_i18n_str_ApicNotPresent;
             return -1;
         }
         threadInfo[nApics].apicId = (buf.ebx >> 24) & 0xff;
         threadInfo[nApics].maxThreadsPerPkg = (buf.ebx >> 16) & 0xff;