On 05/04/10 01:18, roy rosen wrote:
Hi,
2010/5/3, Ian Lance Taylor<i...@google.com>:
roy rosen<roy.1ro...@gmail.com> writes:
1. Is that true that if I try to match in the pattern two insns and in
my code between these insns there is another insn which does not have
any dependency connection to the other two, Is that true that the
peephole would not match in this case? (i.e. the insns to match must
come in the code in sequential order with no other insns between
them)?
Yes.
Was there any special problem implementing such peephole mechanism or
simply nobody tried to work on this yet?
I think it may be very beneficial since I guess that for most
patterns, there are other insns between the pattern's insns which
cause the peephole not to match...
In general, peepholes (in the GCC world) are typically only used when
there is no obvious data dependency between insns and thus the combiner
phase of GCC doesn't know to try and optimize the two (or three)
insns. It has been our experience that peepholes are only
occasionally useful and thus we haven't spent considerable time
improving the infrastructure for the peephole optimizer.
Jeff
