Fix twolf -funroll-loops -O3 miscompilation (a semi-latent web.c bug)

[Steven Bosscher]

On Mon, Nov 19, 2012 at 11:42 PM, Eric Botcazou wrote:
>> That could be done, yes. Cleaning up the REG_EQ* notes requires
>> liveness at the insn level, so it'd require a bigger re-organization
>> of the code. Perhaps adding a new pass (conditional on DF_EQ_NOTES)
>> over all insn in df_lr_finalize, tracking liveness and calling
>> df_remove_dead_eq_notes on each insn.
>>
>> But most passes that use the REG_EQ* notes don't set the DF_EQ_NOTES flag.
>
> Right.  After the DF merge, the de-facto consensus was that individual passes
> were still responsible for cleaning up the REG_EQ* notes when they change the
> code, whereas the REG_DEAD/REG_UNUSED notes are entirely handled by DF.  As
> such, the bug here is in the unroller, not in the webizer.

Then it's in -fsplit-ivs-in-unroller. Looking into it.

Ciao!
Steven