Extended Description

void foo(void);

void s(unsigned a, unsigned b)
{
unsigned x = ~b;

    if (x > 0 && x > a)                                                                             
            foo();                                                                  

}

Clang -O3:

s(unsigned int, unsigned int): # @​s(unsigned int, unsigned int)
cmp esi, -1
je .LBB0_2
not esi
cmp esi, edi
jbe .LBB0_2
jmp foo() # TAILCALL
.LBB0_2:
ret

GCC -O3:
s(unsigned int, unsigned int):
not esi
cmp esi, edi
ja .L4
ret
.L4:
jmp foo()