This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH] SH: New define_split sh.md
- From: Joern Rennecke <joern dot rennecke at superh dot com>
- To: naveens at noida dot hcltech dot com (Naveen Sharma, Noida)
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Wed, 22 Oct 2003 15:53:07 +0100 (BST)
- Subject: Re: [PATCH] SH: New define_split sh.md
> The attached patch does a simple post-reload split
> statements of the form
>
> mov #250, r1
>
> to
> mov #125, r1
> shll r1
>
> SH requires a pc-relative literal pool load for constant data
> more than 2 bytes long. To avoid it, we can synthesize the constant in
> some cases by using a smaller constant and shift operation.
> The rationale behind doing constant synthesis
> is that it would ease the pressure on LS unit
> by converting literal pool loads into two EX group instructions.
> This helps in better scheduling. So this should be a win.
I'm not so sure that this is a win. The pressure on the EX unit is often
higher than that on the LS unit. Besides, you have two instructions
where you had one before.