[LLVMdev] Unnatural loops with O0

[Marc de Kruijf]

Hi Chris,

Is there a compelling reason why llvm-gcc does not always produce natural
loops.  Is it a code size issue, or are there performance implications as
well?  I am seeing a simple 'while' loop compiled to an unnatural loop,
without any gotos, breaks, or continues.  What is the reason for this?

Marc

On Wed, Feb 11, 2009 at 6:51 PM, Chris Lattner <clattner at apple.com> wrote:

>
> On Feb 11, 2009, at 1:13 PM, Marc de Kruijf wrote:
>
> > I am reviving this thread because I am seeing the same thing
> > (unnatural loops produced by llvm-gcc), but it is not limited to -O0
> > -- I am seeing it for -O2 and -O3 as well.
> > Some of my research work is relying on LoopInfo to provide loop
> > information for all loops, but it is missing these loops.  Is there
> > any work in the pipeline that aims to fix this?
>
> Not that I know of.  There has been a project on the open projects
> list to write a pass that converts all loops to natural loops (through
> code duplication).  That would be a nice and self-contained project if
> anyone is interested.
>
> -Chris
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