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Re: Canonicalization of compares performed as side-effect operations

From: "Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>
To: Eric Botcazou <ebotcazou at adacore dot com>
Cc: gcc-patches at gcc dot gnu dot org, Segher Boessenkool <segher at kernel dot crashing dot org>
Date: Mon, 19 Aug 2019 13:49:47 +0100
Subject: Re: Canonicalization of compares performed as side-effect operations
References: <bc94810b-140c-71d4-eca5-9e2c6efae2f7@arm.com> <1787435.c30AEktzrP@arcturus.home> <11fbdb71-c562-27f4-dc94-6c94119bda39@arm.com> <1710505.JbvsNWUeT9@arcturus.home>

On 14/08/2019 08:48, Eric Botcazou wrote:

[Sorry for the delay, I missed your question...]

Interesting.  Does it work for the general case of a reverse subtract,
which I need to handle as wel?


Not clear, Visium only uses it for SNE and combined NEG/SNE.

I worked through the logic. I'm pretty sure it will work for anyunsigned or equality comparison and for any constant. The generaltransformation is


(cst uns/eq/op reg) == (~reg uns/eq/op ~cst)

R.

References:
- Canonicalization of compares performed as side-effect operations
  - From: Richard Earnshaw (lists)
- Re: Canonicalization of compares performed as side-effect operations
  - From: Eric Botcazou
- Re: Canonicalization of compares performed as side-effect operations
  - From: Richard Earnshaw (lists)
- Re: Canonicalization of compares performed as side-effect operations
  - From: Eric Botcazou

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