# HG changeset patch
# User Maximilien Breughe <[email protected]>
# Date 1271144284 -7200
# Branch dev-perflab
# Node ID 401bc1d45798b11db33cf5c995c7c44fceacc4c3
# Parent 9342cbe0c2c9fd94300a3762f518f3d4313f2951
Bug fix: Another branch predictor fix
============================
Branches can cause squashes for 2 reasons:
1) branch prediction
2) branch resolution
Prediction happens in the Decode-stage. At this point, no information is known
about what path is taken.
Therefore a squash caused at prediction-time should not update the branch
predictor and hence the bug fix.
Only squashes resulting from the branch resolution (in the Execution-stage) can
update the branch predictor.
Another possibility was to update the branch predictor only at the
graduation-stage.
diff -r 9342cbe0c2c9 -r 401bc1d45798
src/cpu/inorder/resources/branch_predictor.cc
--- a/src/cpu/inorder/resources/branch_predictor.cc Fri Mar 26 09:57:52
2010 +0100
+++ b/src/cpu/inorder/resources/branch_predictor.cc Tue Apr 13 09:38:04
2010 +0200
@@ -142,10 +142,13 @@
InstSeqNum squash_seq_num, ThreadID tid)
{
DPRINTF(InOrderBPred, "Squashing...\n");
- Addr corr_targ=inst->readPredPC();
- bool taken=inst->predTaken();
- branchPred.squash(squash_seq_num,corr_targ,taken,tid);
-// branchPred.squash(squash_seq_num,tid);
+ if(squash_stage>=ThePipeline::BackEndStartStage){
+ Addr corr_targ=inst->readPredPC();
+ bool taken=inst->predTaken();
+ branchPred.squash(squash_seq_num,corr_targ,taken,tid);
+ }
+ else
+ branchPred.squash(squash_seq_num,tid);
}
void
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