llvm dev - Aug 2010 - [LLVMdev] What may I assume about MachineFunctions.

Upon writing my register allocation algorithm, I am concerned that a load
may be skipped due to a branch.

For instance consider the psudocode

int x = 1
...
if( false )
  load x
  y = 3*x
else
  y = 4*x
...

The load happens in the false block because this is when the variable is
first seen. The load is not preformed in the else block because the register
allocator may see it loaded already.

Do I need to be concerned about cases like this?

Thanks,
Jeff Kunkel
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For the record, the if-else series works as a series of BasicBlocks. See
the http://llvm.org/docs/tutorial/LangImpl6.html page for a more
detailed explanation. But, the simple answer is yes, the allocator does have
to worry about load/stores across blocks.

Thanks,
Jeff Kunkel


On Mon, Aug 30, 2010 at 7:37 AM, Jeff Kunkel <jdkunk3 at gmail.com> wrote:
> Upon writing my register allocation algorithm, I am concerned that a load
> may be skipped due to a branch.
>
> For instance consider the psudocode
>
> int x = 1
> ...
> if( false )
>   load x
>   y = 3*x
> else
>   y = 4*x
> ...
>
> The load happens in the false block because this is when the variable is
> first seen. The load is not preformed in the else block because the
register
> allocator may see it loaded already.
>
> Do I need to be concerned about cases like this?
>
> Thanks,
> Jeff Kunkel
>
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