On Thu, 11 Nov 2010, Ian Lance Taylor wrote:
> roy rosen <roy.1ro...@gmail.com> writes: > > > If I have two insns: > > r2 = r3 > > r3 = r4 > > It seems to me that the dependency analysis creates a dependency > > between the two and prevent parallelization. Although there is a > > dependency (because of r3) I want GCC to parallelize them together. > > Since if the insns are processed together the old value of r3 is used > > for the first insn before it is written by the second insn. > > How do I let GCC know about these things (When exactly each operand is > > used and when it is written)? > > Is it in these hooks? > > In which port can I see a good example for that? > > I was under the impression that an anti-dependence in the same cycle was > permitted to execute. But perhaps I am mistaken. No, you are right. That is the norm when compiling for ia64, for example. I don't think the backend should specifically care about it: the anti-dependency gets zero latency, and the scheduler is able to issue the second instruction on the same cycle after issuing the first. Alexander
