Re: [df] RFA: artifical defs of global registers for EH, etc.

[Kenneth Zadeck <zadeck at naturalbridge dot com>]

your patch is ok on ppc-32 and ia-64.

ok to commit.

kenny


Seongbae Park (박성배, 朴成培) wrote:
> On Jan 8, 2008 3:25 PM, Richard Sandiford <rsandifo@nildram.co.uk> wrote:
>   
>> ""Seongbae Park (박성배, 朴成培)"" <seongbae.park@gmail.com> writes:
>>     
>>> On Jan 8, 2008 2:44 AM, Richard Sandiford <rsandifo@nildram.co.uk> wrote:
>>>       
>>>> The LR confluence function is:
>>>>
>>>>   /* Call-clobbered registers die across exception and call edges.  */
>>>>   /* ??? Abnormal call edges ignored for the moment, as this gets
>>>>      confused by sibling call edges, which crashes reg-stack.  */
>>>>   if (e->flags & EDGE_EH)
>>>>     bitmap_ior_and_compl_into (op1, op2, df_invalidated_by_call);
>>>>   else
>>>>     bitmap_ior_into (op1, op2);
>>>>
>>>>   bitmap_ior_into (op1, df->hardware_regs_used);
>>>>
>>>> But global registers are df_invalidated_by_call, so this means
>>>> that there are no reaching definitions for a global register before
>>>> the first definition in the exception handler itself.
>>>>         
>>> Really? All calls are supposed to have both USE and DEF for global_regs[],
>>> so calls themselves should be treated as the definition for global_regs.
>>>       
>> Sorry, I quoted the wrong thing.  It isn't the LR confluence function
>> that matters, it's the reaching definitions function.  My point was
>> supposed to be that we don't propagate global definitions from the
>> source of an EH edge to the destination because all such registers
>> are invalidated_by_call.
>>
>>     
>>> The only thing I see missing is global_regs[] missing from entry_block_defs,
>>> which we probably should add to.
>>>       
>> Yes, that probably is missing too but...
>>
>>     
>>> So, would it be sufficient to add global_regs to entry_block_defs ?
>>>       
>> ...it isn't enough on its own.
>>     
>
> Now I see what you meant. Because df_rd_confluence_n ()
> blows away everything that's df_invalidated_by_call
> (through {sparse,dense}_invalidated)
> whenever it sees an EH_EDGE,
> the first use of a global within the EH region would look
> without any reaching def (i.e. uninitialized).
>
> I think your patch is the right approach.
>
> Approved, unless Kenny (or anybody else) finds a regression in his testing.
>
>   
>> Anyway, I'm wondering about doing the MIPS thing a different way,
>> so if there's doubt, we might as well drop this patch.
>>
>> Richard
>>     
>
> Seongbae
>