From: "Stefan Kanthak" <stefan.kanthak@nexgo.de>
To: "Paul Koning" <paulkoning@comcast.net>
Cc: <gcc@gnu.org>
Subject: Re: Widening multiplication, but no narrowing division [i386/AMD64]
Date: Mon, 9 Jan 2023 16:20:37 +0100 [thread overview]
Message-ID: <3BFE5710A2B04DA89EC334177EC28BC6@H270> (raw)
In-Reply-To: <A2650E81-2627-4F3C-A531-1D4944C338AB@comcast.net>
"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
next prev parent reply other threads:[~2023-01-09 15:25 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 [this message]
2023-01-09 15:30 ` Paul Koning
2023-01-09 16:27 ` Stefan Kanthak
2023-01-10 16:49 ` Paul Koning
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