From: Paul Koning <paulkoning@comcast.net>
To: Stefan Kanthak <stefan.kanthak@nexgo.de>
Cc: gcc@gnu.org
Subject: Re: Widening multiplication, but no narrowing division [i386/AMD64]
Date: Mon, 9 Jan 2023 10:30:30 -0500 [thread overview]
Message-ID: <46F8B35E-93C9-4B76-90C1-217291D6509A@comcast.net> (raw)
In-Reply-To: <3BFE5710A2B04DA89EC334177EC28BC6@H270>
> On Jan 9, 2023, at 10:20 AM, Stefan Kanthak <stefan.kanthak@nexgo.de> wrote:
>
> "Paul Koning" <paulkoning@comcast.net> wrote:
>
>>> On Jan 9, 2023, at 7:20 AM, Stefan Kanthak <stefan.kanthak@nexgo.de> wrote:
>>>
>>> Hi,
>>>
>>> GCC (and other C compilers too) support the widening multiplication
>>> of i386/AMD64 processors, but DON'T support their narrowing division:
>>
>> I wonder if this changed in the recent past.
>> I have a pattern for this type of thing in pdp11.md:
> [...]
>> and I'm pretty sure this worked at some point in the past.
>
> Unfortunately the C standard defines that the smaller operand (of lesser
> conversion rank), here divisor, has to undergo a conversion to the "real
> common type", i.e. the broader operand (of higher conversion rank), here
> dividend. Unless the information about promotion/conversion is handed over
> to the code generator it can't apply such patterns -- as demonstrated by
> the demo code.
>
> regards
> Stefan
Yes, I was thinking the same. But I spent a while on that pattern -- I wanted to support div/mod as a single operation because the machine has that primitive. And I'm pretty sure I saw it work before I committed that change. That's why I'm wondering if something changed.
paul
next prev parent reply other threads:[~2023-01-09 15:30 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-09 12:20 Stefan Kanthak
2023-01-09 13:10 ` LIU Hao
2023-01-09 13:19 ` Stefan Kanthak
2023-01-09 14:23 ` Paul Koning
2023-01-09 15:20 ` Stefan Kanthak
2023-01-09 15:30 ` Paul Koning [this message]
2023-01-09 16:27 ` Stefan Kanthak
2023-01-10 16:49 ` Paul Koning
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