Re: PATCH COMMITTED: Use conditional moves in groups of assignments

[Paolo Bonzini <paolo dot bonzini at lu dot unisi dot ch>]

> > > Note we have two conditional forms in RTL: cond_exec and if_then_else.
> > >
> > > COND_EXEC is uses when all side effects are suppressed when the insn
> > > fails its condition.  IF_THEN_ELSE is used for situations where the
> > > side-effects are performed even if the value is not used.  So
> >
> > That looks wrong: the false if_then_else arm isn't supposed to
> > be executed *at all* i.e. not for side-effects like
> > post-increment.  It's not logical; the false if_then_else arm of
> > a conditional branch using if_then_else evaluated (usually just
> > a label; but the address isn't evaluated for validity).
>
> It's not wrong.  Consider the case where the false arm needs reloads. 
> The reloads are unconditionally executed.

Apart from this (which may be considered an implementation nit), what 
Richard is saying makes sense to me.  Nothing in RTL is ever 
short-circuited, except COND_EXEC.  If I am not mistaken, combine relies 
heavily on this by constructing IF_THEN_ELSE expressions more or less 
arbitrarily.

Paolo