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Subject: Re: [Documentation] Correct RTL documentation: (use (mem ...)) is
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From: Jeff Law <jeffreyalaw@gmail.com>
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On 7/23/22 03:26, Roger Sayle wrote:
> This patch is a one line correction/clarification to GCC's current
> RTL documentation that explains a USE of a MEM is permissible.
>
> PR rtl-optimization/99930 is an interesting example on x86_64 where
> the backend generates better code when a USE is a (const) MEM than
> when it is a REG. In fact the backend relies on CSE to propagate the
> MEM (a constant pool reference) into the USE, to enable combine to
> merge/simplify instructions.
>
> This change has been tested with a make bootstrap, but as it might
> provoke a discussion, I've decided to not consider it "obvious".
> Ok for mainline (to document the actual current behavior)?
>
>
> 2022-07-23  Roger Sayle   <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
>          * doc/rtl.texi (use): Document that the operand may be a MEM.

Given this is documenting existing behavior and it's not hard to 
envision the MEM being useful in this context.  OK.

jeff