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From: Segher Boessenkool <>
To: Roger Sayle <>
Subject: Re: [PATCH] Add new target hook: simplify_modecc_const.
Date: Wed, 27 Jul 2022 13:37:06 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <003501d8a18d$c22ed760$468c8620$>

On Wed, Jul 27, 2022 at 08:51:58AM +0100, Roger Sayle wrote:
> > They can be, as clearly documented (and obvious from the code), but you
> can
> > not ever have that in the RTL stream, which is needed for your patch to do
> > anything.
> That's the misunderstanding; neither this nor the previous SUBREG patch,
> affect/change what is in the RTL stream, no COMPARE nodes are every
> changed or modified, only eliminated by the propagation/fusion in combine
> (or CSE).

There are no guarantees at all for that though?

> We have --enable-checking=rtl to guarantee that the documented invariants
> always hold in the RTL stream.

That unfortunately only checks a few structural constraints, and not
even all.  For example not that STRICT_LOW_PART has a SUBREG as
argument, which is documented, and the only thing that makes sense
anyway.  This is PR106101.  Unfortunately many targets violate this.


  reply	other threads:[~2022-07-27 18:38 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-07-07 21:08 [PATCH] Be careful with MODE_CC in simplify_const_relational_operation Roger Sayle
2022-07-07 22:38 ` Segher Boessenkool
2022-07-26 12:13   ` [PATCH] Add new target hook: simplify_modecc_const Roger Sayle
2022-07-26 17:44     ` Segher Boessenkool
2022-07-26 21:04       ` Roger Sayle
2022-07-26 22:11         ` Segher Boessenkool
2022-07-27  7:51           ` Roger Sayle
2022-07-27 18:37             ` Segher Boessenkool [this message]
2022-07-28 12:39         ` Richard Sandiford
2022-10-10 15:50           ` H.J. Lu
2022-10-14 20:31             ` Jeff Law
2022-10-14 21:05               ` H.J. Lu
2022-10-14 20:26       ` Jeff Law

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