Review Board 2.0.15


Branch predictor: Fixes the tournament branch predictor.

Review Request #747 - Created June 16, 2011 and submitted - Latest diff uploaded

Information
Ali Saidi
gem5
Reviewers
Default
ali, gblack, nate, stever
Branch predictor: Fixes the tournament branch predictor.

Branch predictor could not predict a branch in a nested loop because:
 1. The global history was not updated after a mispredict squash.
 2. The global history was updated in the fetch stage. The choice predictors
    that were updated  used the changed global history. This is incorrect, as
    it incorporates the state of global history after the branch in
    encountered. Fixed update to choice predictor using the global history
    state before the branch happened.
 3. The global predictor table was also updated using the global history state
    before the branch happened as above.

Additionally, parameters to initialize ctr and history size were reversed.
All regressions produce correct output. Provides up to an additional 10% performance improvement over fetch stage patch and can now correctly predict nested branches.