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Re: ARM THUMB: fundamental bug in handling of far jumps?
- From: Richard Earnshaw <rearnsha at arm dot com>
- To: Adrian von Bidder <avbidder at acter dot ch>
- Cc: Richard Henderson <rth at redhat dot com>, gcc devel mailing list <gcc at gcc dot gnu dot org>, Richard dot Earnshaw at arm dot com
- Date: Wed, 30 Jan 2002 11:35:49 +0000
- Subject: Re: ARM THUMB: fundamental bug in handling of far jumps?
- Organization: ARM Ltd.
- Reply-to: Richard dot Earnshaw at arm dot com
> On Tue, 2002-01-29 at 22:46, Richard Henderson wrote:
>
> > Not-taken branches are normally better for performance. Might not
> > apply to the thumb though.
>
> afaict at least on arm7tdmi branches are indifferent
It would be best to consider the arm7 (and arm9 and StrongARM) as
predicting all branches as not-taken. The cost in all cases of not taking
the branch is 1 cycle (the branch insn itself). The cost of taking the
branch is a pipeline refill (2 to 5 cycles depending on the processor).
R.