Code performance regression between gcc 4.5 and 4.6

[Martin Reinecke]

Hi,

while benchmarking a numerical C library making heavy use of SSE2
intrinsics, I have noticed a significant (around 10 percent) slowdown
in the code generated by the current gcc trunk, compared to the one
produced by the 4.5.1 release.
It's quite hard to reduce the code to a small test case, but I can easily
point out the hot code regions where most of the CPU time is spent.
Do you think I should open a PR for this, or is this kind of performance
fluctuation to be expected?

Cheers,
  Martin