extra instructions lost from -O0 to -O1

[Thomas A.M. Bernard]

Well I found another way to solve the problem by updating the dce for 
not taking out my instructions.

I inserted "setallocate" as a native operator in the back-end which 
comes from a GIMPLE node and map to the RTL pattern. Earlier in the 
discussion, it's been discussed that the dce was taking out the 
instruction when flag -O1 was engaged. To solve that, in 
'tree-ssa-dce.c', I flagged this node with the function, 
"mark_stmt_necessary". And it works fine so far. The instruction is not 
omitted anymore by the dce :-)

Thanks for your help guys.
Thomas

Ian Lance Taylor wrote:
> "Thomas A.M. Bernard" <t.bernard@uva.nl> writes:
>
>   
>> Ian Lance Taylor wrote:
>>     
>>> "Thomas A.M. Bernard" <t.bernard@uva.nl> writes:
>>>
>>>   
>>>       
>>>> I guess I am missing something here. I've tried the following as Paolo
>>>> suggested,
>>>>
>>>> (define_insn "setallocate"
>>>> [(unspec_volatile:DI [(match_operand:DI 0 "general_operand" "r")]
>>>>                                 UNSPEC_ALLOCATE)]
>>>>  ""
>>>>  "allocate %0\t\t#TCB_INSTRUCTIONS"  [(set_attr "type" "multi")])
>>>>
>>>> When flag -O0 is on, everything's fine. But when flag -O1 is engaged,
>>>> the instruction is still omitted. Something missing ?
>>>>     
>>>>         
>>> The only that gcc will remove an unspec_volatile instruction is if it
>>> is on a code path which is never executed.
>>>   Look at the RTL dump files (from, e.g., -fdump-rtl-all), see where
>>> it
>>> is disappearing, and why.
>>>   
>>>       
>> With this pattern for setallocate, when the flag -O1 is engaged, the
>> instruction is already omitted just at the expansion. As Ian
>> mentioned, I suspect the problem comes from the fact that the compiler
>> thinks this code path won't be executed. I presume this should be done
>> at the CFG level. I added in CFG a "node" which describes
>> setallocate' Any clue to say explicitly this will be executed in any
>> case ?
>>     
>
> The conventional way to get a special purpose instruction through the
> tree code is to use a builtin function.  For example, look at the
> calls to __builtin_XXX in config/i386/mmintrin.h (a header file
> included by target programs) and the associated code in
> config/i386/i386.c.
>
> Ian
>