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Re: [Committed] PR24427: Folding (X&C1)|C2 and (X|C1)&C2
- From: Andrew Pinski <pinskia at physics dot uc dot edu>
- To: roger at eyesopen dot com (Roger Sayle)
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Mon, 13 Feb 2006 13:39:53 -0500 (EST)
- Subject: Re: [Committed] PR24427: Folding (X&C1)|C2 and (X|C1)&C2
>
>
> The following patch resolves PR middle-end/24427 by implementing several
> constant folding transformations of bitwise-AND and bitwise-OR of a
> constant combinations.
>
> With this patch we now canonicalize (X|C1)&C2 as (X&C3)|C4 where we
> always perform the bitwise-AND first, followed by the IOR. This
> allows later optimizers to see the BIT_IOR_EXPR outermost, and imply
> non-zeroness. Additionally, the patch implements several further
> optimizations such as "(X & 1) | 1" -> "(X,1)" and "(X & ~1) | 1" ->
> "X | 1". Finally, as a canonicalization step, BIT_AND_EXPR's constant
> is simplified to the constant with the fewest set bits. This converts
> "(X & 6) | 2" into the equalivalent "(X & 4) | 2". This should help
> code generation on some platforms.
>
> Committed to mainline as revision 110918.
>
> 2006-02-13 Roger Sayle <roger@eyesopen.com>
>
> PR middle-end/24427
> * fold-const.c (fold_binary) <BIT_IOR_EXPR>: Transform (X&C1)|C2
> into (X,C2) if C1 is a subset of the bits of C2. Transform
> (X&C1)|C2 into X|C2 if C1|C2 == ~0. Canonicalize (X&C1)|C2 as
> (X&(C1&~C2))|C2.
> <BIT_AND_EXPR>: Canonicalize (X|C1)&C2 as (X&C2)|(C1&C2).
>
> * gcc.dg/tree-ssa/andor-1.c: New test case.
This also fixes PR 23670.
Thanks,
Andrew Pinski