BP: Fix several Branch Predictor issues.

1. Updates the Branch Predictor correctly to the state
   just after a mispredicted branch, if a squash occurs.
2. If a BTB does not find an entry, the branch is predicted not taken.
   The global history is modified to correctly reflect this prediction.
3. Local history is now updated at the fetch stage instead of
   execute stage.
4. In the Update stage of the branch predictor the local predictors are
   now correctly updated according to the state of local history during
   fetch stage.

This patch also improves performance by as much as 17% on some benchmarks

1 files changed, 4 insertions, 0 deletions

diff --git a/src/cpu/o3/decode_impl.hh b/src/cpu/o3/decode_impl.hh
index 60bca1041..22b89f4a8 100644
--- a/src/cpu/o3/decode_impl.hh
+++ b/src/cpu/o3/decode_impl.hh
@@ -278,11 +278,15 @@ DefaultDecode<Impl>::squash(DynInstPtr &inst, ThreadID tid)
     // Send back mispredict information.
     toFetch->decodeInfo[tid].branchMispredict = true;
     toFetch->decodeInfo[tid].predIncorrect = true;
+    toFetch->decodeInfo[tid].mispredictInst = inst;
     toFetch->decodeInfo[tid].squash = true;
     toFetch->decodeInfo[tid].doneSeqNum = inst->seqNum;
     toFetch->decodeInfo[tid].nextPC = inst->branchTarget();
     toFetch->decodeInfo[tid].branchTaken = inst->pcState().branching();
     toFetch->decodeInfo[tid].squashInst = inst;
+    if (toFetch->decodeInfo[tid].mispredictInst->isUncondCtrl()) {
+            toFetch->decodeInfo[tid].branchTaken = true;
+    }
 
     InstSeqNum squash_seq_num = inst->seqNum;