From: Peter Bergner <bergner@linux.ibm.com>
To: Jeff Law <jeffreyalaw@gmail.com>,
Ajit Agarwal <aagarwa1@linux.ibm.com>,
gcc-patches <gcc-patches@gcc.gnu.org>
Cc: Segher Boessenkool <segher@kernel.crashing.org>,
Richard Biener <richard.guenther@gmail.com>
Subject: Re: [PATCH] rtl-optimization: ppc backend generates unnecessary signed extension.
Date: Thu, 23 Mar 2023 11:53:04 -0500 [thread overview]
Message-ID: <247f5af3-5db3-4a73-b636-95e006a3a649@linux.ibm.com> (raw)
In-Reply-To: <1a482ac5-404b-0787-c682-b10d13dc76ee@gmail.com>
On 3/23/23 11:32 AM, Jeff Law via Gcc-patches wrote:
> On 3/23/23 10:29, Peter Bergner wrote:
>> I'm sorry that I don't know how REE works. Why can't it optimize this?
>> I see in the REE dump:
>>
>> (insn 20 18 22 3 (set (reg:DI 4 4)
>> (zero_extend:DI (reg:QI 4 4 [orig:120 cD.3556+3 ] [120]))) "pr41742.c":6:41 8 {zero_extendqidi2} (nil))
>> (call_insn 22 20 41 3 (parallel [
>> (set (reg:DI 3 3)
>> (call (mem:SI (symbol_ref:DI ("memset") [flags 0x41] <function_decl 0x7fff925f8400 __builtin_memset>) [0 memsetD.1196 S4 A8])
>> (const_int 64 [0x40])))
>> (use (const_int 0 [0]))
>> (clobber (reg:DI 96 lr)) ...
>>
>> Is there a reason why REE cannot see that our (reg:QI 4) is a param register
>> and thus due to our ABI, already correctly sign/zero extended?
>
> I don't think REE has ever considered exploiting ABI constraints. Handling
> that might be a notable improvement on various targets. It'd be a great
> place to do some experimentation.
Ok, so sounds like a good follow-on project after this patch is reviewed
and committed (stage1). Thanks for your input!
Peter
next prev parent reply other threads:[~2023-03-23 16:53 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-23 10:38 Ajit Agarwal
2023-03-23 12:38 ` Peter Bergner
2023-03-23 15:32 ` Ajit Agarwal
2023-03-23 15:32 ` Ajit Agarwal
2023-03-23 16:29 ` Peter Bergner
2023-03-23 16:32 ` Jeff Law
2023-03-23 16:53 ` Peter Bergner [this message]
2023-03-23 23:12 ` Jeff Law
2023-03-24 21:34 ` Peter Bergner
2023-03-25 18:09 ` Jeff Law
2023-03-31 0:01 ` Hans-Peter Nilsson
2023-03-31 14:01 ` Jeff Law
2023-03-23 13:47 ` Jeff Law
2023-03-23 15:36 ` Ajit Agarwal
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