Re: A Query regarding jump pattern
On Mon, Apr 14, 2008 at 11:07 PM, Ian Lance Taylor [EMAIL PROTECTED] wrote: Mohamed Shafi [EMAIL PROTECTED] writes: I have read in the internals that indirect_jump and jump pattern are necessary in any back-end for the compiler to be build and work successfully. For any back-end there will be some limitation as to how big the offset used in the jump instructions can be. If the offset is too big then the indirect_jump pattern has to utilized. Now my question is how will i be able to specify the limit of the offset so the gcc generates indirect_jump pattern instead of the jump pattern? I hope i am clear. From the perspective of insn names, it's not quite accurate to say that jump turns into indirect_jump. It would be more correct to say that when there is a limit to the offset for jump, it needs to use a register. The way to handle this is to set the length attribute correctly for each insn, and to change code generation based on the length. See, e.g., the mips.md jump insn for an example. Ok , looking at another reply from Jim (http://gcc.gnu.org/ml/gcc/2008-04/msg00311.html), where he suggests to use shorten_branhes in reorg and generate indirect branch, it looks like i will have to reserve a register. Am i right? If that is the case it seems that there is no need for a indirect_jump pattern. So can you tell me when exactly are the indirect_jump patterns will be utilized by gcc? Regards, Shafi
Re: A Query regarding jump pattern
Mohamed Shafi [EMAIL PROTECTED] writes: Ok , looking at another reply from Jim (http://gcc.gnu.org/ml/gcc/2008-04/msg00311.html), where he suggests to use shorten_branhes in reorg and generate indirect branch, it looks like i will have to reserve a register. Am i right? You will have to do something. Having the jump pattern require a scratch register is one approach. For a much more complicated approach, see sh.md. If that is the case it seems that there is no need for a indirect_jump pattern. So can you tell me when exactly are the indirect_jump patterns will be utilized by gcc? indirect_jump jumps to a value held in a register. jump jumps to a constant location. indirect_jump is used for things like the gcc label extension. Ian
Re: A Query regarding jump pattern
Mohamed Shafi [EMAIL PROTECTED] writes: I have read in the internals that indirect_jump and jump pattern are necessary in any back-end for the compiler to be build and work successfully. For any back-end there will be some limitation as to how big the offset used in the jump instructions can be. If the offset is too big then the indirect_jump pattern has to utilized. Now my question is how will i be able to specify the limit of the offset so the gcc generates indirect_jump pattern instead of the jump pattern? I hope i am clear. From the perspective of insn names, it's not quite accurate to say that jump turns into indirect_jump. It would be more correct to say that when there is a limit to the offset for jump, it needs to use a register. The way to handle this is to set the length attribute correctly for each insn, and to change code generation based on the length. See, e.g., the mips.md jump insn for an example. Ian
A Query regarding jump pattern
Hello all, I have read in the internals that indirect_jump and jump pattern are necessary in any back-end for the compiler to be build and work successfully. For any back-end there will be some limitation as to how big the offset used in the jump instructions can be. If the offset is too big then the indirect_jump pattern has to utilized. Now my question is how will i be able to specify the limit of the offset so the gcc generates indirect_jump pattern instead of the jump pattern? I hope i am clear. Thank you for your time. Regards, Shafi
