From: Segher Boessenkool <segher@kernel.crashing.org>
To: Andrew Stubbs <andrew_stubbs@mentor.com>
Cc: GCC Development <gcc@gcc.gnu.org>
Subject: Re: RTL alternative selection question
Date: Mon, 23 Sep 2019 14:15:00 -0000 [thread overview]
Message-ID: <20190923141517.GH9749@gate.crashing.org> (raw)
In-Reply-To: <1a7febb4-197e-eca7-4fcf-99bf5cb8bdf6@mentor.com>
On Mon, Sep 23, 2019 at 11:56:27AM +0100, Andrew Stubbs wrote:
> [(set (match_operand:DI 0 "register_operand" "=Sg,v")
> (ashift:DI
> (match_operand:DI 1 "gcn_alu_operand" " Sg,v")
> (match_operand:SI 2 "gcn_alu_operand" " Sg,v")))
> (clobber (match_scratch:BI 3 "=cs,X"))]
> Unfortunately, the compiler (almost?) exclusively selects the second
> alternative, even when this means moving the values from one register
> file to the other, and then back again.
>
> The problem is that the scalar instruction clobbers the CC register,
> which results in a "reject++" for that alternative in the LRA dump.
What kind of reject? It prints a reason, too.
Maybe we should make a macro/hook to never do that for your target, for
those flags registers anyway.
Segher
next prev parent reply other threads:[~2019-09-23 14:15 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-23 10:56 Andrew Stubbs
2019-09-23 13:23 ` Richard Biener
2019-09-23 14:15 ` Segher Boessenkool [this message]
2019-09-23 14:39 ` Andrew Stubbs
2019-09-23 15:21 ` Segher Boessenkool
2019-09-23 15:26 ` Andrew Stubbs
2019-09-23 16:24 ` Jeff Law
2019-09-23 19:14 ` Richard Sandiford
2019-10-01 12:12 ` Andrew Stubbs
2019-10-02 0:07 ` Segher Boessenkool
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