Re: [PATCH] Better __ashlDI3, __ashrDI3 and __lshrDI3 functions, plus fixed __bswapsi2 function

[Jeff Law <law@redhat.com>]

On 11/10/20 2:09 PM, Jeff Law wrote:
> On 11/10/20 1:14 PM, Jakub Jelinek via Gcc-patches wrote:
>> On Tue, Nov 10, 2020 at 08:44:32PM +0100, Stefan Kanthak wrote:
>>> Eric Botcazou <botcazou@adacore.com> wrote:
>>>
>>>>> The implementation of the __ashlDI3(), __ashrDI3() and __lshrDI3() functions
>>>>> is rather bad, it yields bad machine code at least on i386 and AMD64. Since
>>>>> GCC knows how to shift integers twice the register size these functions can
>>>>> be written as one-liners.
>>>> These functions are precisely meant to be used when GCC cannot do that.
>>> On which processor(s) is GCC unable to generate code for DWtype shifts?
>> E.g. avr-none, msp430-elf, pdp11-aout.
>> And I see recursive __cmpdi2 calls on avr-none too.
> ACK.  I'll pull those [u]cmpdi changes.  They were iffy at best, this
> confirms the concerns we both had.
I'm not seeing recursive calls.  I'm seeing ucmpdi calling cmpdi on avr
(and cmpdi is simple straightline code with no calls, so no recursion). 
msp looks OK WRT [u]cmpdi as does pdp11.

So I think unless we see something clearly wrong we should leave the
committed patch as-is.  There's the follow-up for abs and more multiply
stuff that still needs a looksie as well as subsequent independent patches.

Jeff