[PATCH] Added a new register class for Thumb PC-rel loads

[Evan Cheng]

It would make it easier to review if you can illustrate the change with some assembly code sequence.

Evan

On Aug 8, 2013, at 7:30 AM, Daniel Stewart <stewartd at codeaurora.org> wrote:

> This patch is for allowing a jump table (in Thumb mode) to not use the LR register, which can branch mispredicts during a mov lr, pc. If it could be reviewed, I’d appreciate it.
>  
> This patch does the following:
>  
> - Query for the GPRPair with gsub_1 in rGPR class.
> This replaces the hard-coded reference
>  
> - Add jtGPR register class to be used by load PC relative
> address for jump table that avoids the use of LR register.
> This prevents the codegen from generating mov pc, lr
> which causes the target to think it is returning
> from a function and predict that the next address will
> be in the calling function.
>  
> Daniel Stewart
> --
> Qualcomm Innovation Center, Inc is a member of Code Aurora Forum, hosted by The Linux Foundation
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