[PATCH] Improve combining of conditionals

[Maxim Kuvyrkov]

On Apr 15, 2011, at 3:34 PM, Eric Botcazou wrote:

>> The problem this patch fixes is that combine_simplify_rtx() prefers to
>> return an expression (say, <xor (a) (b)>) even when a comparison is
>> prefered (say, <neq (xor (a) (b)) 0>).  Expressions are not recognized as
>> valid conditions of if_then_else for most targets, so combiner misses a
>> potential optimization.  This patch makes combine_simplify_rtx() aware of
>> the context it was invoked in, and, when appropriate, does not discourage
>> it from returning a conditional.
> 
> Btw, this is very likely also valid for targets with STORE_FLAG_VALUE == -1 so 
> the same IN_COND short-circuit would need to be added a few lines below in 
> combine_simplify_rtx.  But this would need to be tested.  Do you happen to 
> have access to such a target, e.g. m68k?

Hm, I didn't notice that one, thanks!  I have access to m68k (ColdFire, tbp) and will test this change there before committing.

--
Maxim Kuvyrkov
Mentor Graphics / CodeSourcery