On Wed, Oct 10, 2012 at 7:33 PM, Jonathan Neuschäfer
<j.neuschaefer@xxxxxxx> wrote:
> I can't say with certainty that it's safe either, so I probably should
> have marked the patch with "request for comments".
>
> AFAICT there are three reasons an instruction cannot be moved up or down
> within a basic block:
> 1. If it takes previous SSA values as arguments, it can't be moved
> above the corresponding intructions.
> 2. If its value is used as an argument of an instruction further down
> in the BB, it can't be moved below that instruction.
> 3. Swapping two instructions that influence or are influenced by the
> "global state" (sorry for the loose wording), e.g. by doing memory
> accesses, performing I/O, or calling functions (which in turn can
> do about anything in general), is generally unsafe.
>
> Case 1 doesn't apply because PHI nodes don't use values computed in the
> same invocation of their basic block. Case 2 doesn't apply as I'm not
> moving the PHI nodes down. Case 3 doesn't seem to apply either.
>
> That's how I think this patch is safe.
Sounds plausible but I'm still uneasy with the idea that LLVM backend
needs to reshuffle instructions like this.
Would it be possible to solve this in the frontend?
Pekka
--
To unsubscribe from this list: send the line "unsubscribe linux-sparse" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
