From: "Stefan Kanthak" <stefan.kanthak@nexgo.de>
To: <gcc@gnu.org>, "LIU Hao" <lh_mouse@126.com>
Subject: Re: Will GCC eventually support SSE2 or SSE4.1?
Date: Fri, 26 May 2023 17:40:57 +0200 [thread overview]
Message-ID: <8981EF5CCEFB42B7B563B35A0B939FE5@H270> (raw)
In-Reply-To: <ddd532eb-31fc-f6ce-7eef-9269954ba799@126.com>
You wrote:
>在 2023-05-26 14:46, Stefan Kanthak 写道:
>> OOPS: why does GCC (ab)use the SSE2 alias "Willamette New Instruction Set"
>> (... ...)
>> OUCH: why does it FAIL to REALLY use SSE2, as shown in the comments on the
>> right side?
>
> Please stop yelling like that. It makes you look like a naughty pupil.
That's EMPHASISING, kid!
>> 14 instructions in 33 bytes # 11 instructions in 32 bytes
>>
>> OUCH: why does GCC abuse EBX (and ECX too) and performs a superfluous
>> memory write?
>
> Apart from the SSE question: You are performing 64-bit arithmetic on a 32-bit
> machine, which GCC isn't good at.
So it's REALLY time to fix that.
> The preferred way to check whether a 64-bit integer is a power of two is to cast it
> to a float, then examine whether its 23-bit mantissa is all zeroes:
Feel free to propose this alternative here (better elsewhere, where you'll
earn less laughter).
But don't forget that this 23-bit mantissa will be all zeroes for quite some
64-bit (and even 32-bit) integers which are no power of 2, for example
0x8000003fffffffff, and that both FILD and CVT2SI2SS only work on SIGNED
integers.
I instead prefer to show that and how GCCs current code generator fails to
optimise properly.
Stefan
next prev parent reply other threads:[~2023-05-26 15:53 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-26 6:46 Stefan Kanthak
2023-05-26 7:00 ` Andrew Pinski
2023-05-26 7:30 ` Jonathan Wakely
2023-05-26 7:58 ` Stefan Kanthak
2023-05-26 8:16 ` Sam James
2023-05-26 8:28 ` Jonathan Wakely
2023-05-26 8:59 ` Stefan Kanthak
2023-05-26 9:22 ` Jakub Jelinek
2023-05-26 11:28 ` Stefan Kanthak
2023-05-26 11:42 ` Jonathan Wakely
2023-05-26 12:03 ` Stefan Kanthak
2023-05-26 12:16 ` Jonathan Wakely
2023-05-26 12:22 ` Stefan Kanthak
2023-05-26 13:00 ` Mark Wielaard
2023-05-26 12:23 ` Jonathan Wakely
2023-05-26 11:36 ` Stefan Kanthak
2023-05-26 11:45 ` Jonathan Wakely
2023-05-26 12:19 ` Stefan Kanthak
2023-05-26 12:30 ` Jonathan Wakely
2023-05-26 12:42 ` Stefan Kanthak
2023-05-26 13:33 ` Nicholas Vinson
2023-05-26 12:37 ` Jakub Jelinek
2023-05-26 13:49 ` Stefan Kanthak
2023-05-26 14:07 ` Jonathan Wakely
2023-05-26 14:18 ` Jakub Jelinek
2023-05-26 14:41 ` Stefan Kanthak
2023-05-26 14:55 ` Jonathan Wakely
2023-05-26 15:07 ` Stefan Kanthak
2023-05-26 14:26 ` Stefan Kanthak
2023-05-26 14:58 ` Jonathan Wakely
2023-05-26 15:49 ` Stefan Kanthak
2023-05-26 16:44 ` David Brown
2023-05-27 18:16 ` Will GCC eventually support correct code compilation? Dave Blanchard
2023-05-27 18:59 ` Jason Merrill
2023-05-28 11:50 ` David Brown
2023-05-26 9:22 ` Will GCC eventually support SSE2 or SSE4.1? Jonathan Wakely
2023-05-26 8:12 ` Hagen Paul Pfeifer
2023-05-26 9:51 ` Jonathan Wakely
2023-05-26 11:34 ` Nicholas Vinson
2023-05-26 15:10 ` LIU Hao
2023-05-26 15:40 ` Stefan Kanthak [this message]
2023-05-27 18:20 ` LIU Hao
2023-05-27 18:49 ` Stefan Kanthak
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