Hi Stephen,
snipped
>
> > > > > > > >
> > > > > > > > >
> > > > > > > > > > + if ((ret) | (!is_leaf))
> > > > > > > > > > +
> > > > > > > > >
> > > > > > > > > Is the operator here should be || ?
> > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > > > Check is done for 'if either ret is not 0 or if it ret is
> > > > > > > > 0 but not leaf' we skip leaf details print. If 'ret is 0 and is
> > > > > > > > leaf'
> > > > > > > > we skip continue to print
> > > > > > > leaf details.
> > > > > > >
> > > > > > > IMO, using logical operator over bitwise operator is good
> > > > > > > here in if statement
> > > > > > .
> > > > > > > Like below.?
> > > > > > >
> > > > > > > If (ret || (is_leaf == 0 ))
> > > > > >
> > > > > > Thanks for the information, if the logic is correct do I need
> > > > > > to change for v6
> > > > > >
> > > > >
> > > > > OK in v6, but you can wait to hear more comments from others if
> > > > > any before sending v6 .
> > > >
> > > > Ok thanks Reshma, but can you tell me how the earlier logic fails
> > > > and runs slow compared to logical or?
> > >
> > > Not about faster or slower.
> >
> > Now I see, I was wondering the suggestion was for improvement for
> performance.
> >
> > >
> > > Logical operators are commonly used in decision making in C programming.
> > > Bitwise operators are used in C programming to perform bit-level
> > > operations.
> > >
> >
> > Agreed
> >
> > > Since , above if condition is for decision making here logical ||
> > > operator will fit , so I am suggesting to use that.
> > >
> >
> > But bitwise OR is not wrong right?
> >
> > > We don't need to do any bitwise manipulation in if condition to
> > > make the decision, so bitwise | operator is not needed
> >
> > We can correct this in next patch set not v6 if this is only change for
> > 'show tm'
>
> It could be that compiler might optimize logical into bitwise operation to
> avoid
> cost of conditional branch (if there are no side effects).
Checking with 'EXTRA_CFLAGS=-g' we get the code generated as
"""
if ((ret) | (!is_leaf))
9a512: 8b 85 28 fd ff ff mov eax,DWORD PTR [rbp-0x2d8]
9a518: 85 c0 test eax,eax
9a51a: 0f 94 c0 sete al
9a51d: 0f b6 c0 movzx eax,al
9a520: 0b 85 3c fd ff ff or eax,DWORD PTR [rbp-0x2c4]
9a526: 85 c0 test eax,eax
9a528: 75 74 jne 9a59e <show_tm+0x73e>
continue;
"""
Looks like the is_leaf is picked assembly 'test' is done then byte is set to 1
based on flags. This is then or with 'ret'. I think your observation is correct
'compiler is remapping to or'
Thanks
Vipin Varghese
