cpu: Added parameters to enable/disable features in LTAGE

They are for the following features in the LTAGE loop predictor:
 - Hashing for calculating the loop table entry
 - Add direction information
 - Add speculative iteration number information

Change-Id: I395f4526163ee0d0229d1e87cde2bb046f1dd43a
Signed-off-by: Pau Cabre <pau.cabre@metempsy.com>
Reviewed-on: https://gem5-review.googlesource.com/c/14597
Reviewed-by: Ilias Vougioukas <ilias.vougioukas@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Louis Delhez <ldelhez@ucla.edu>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/src/cpu/pred/BranchPredictor.py b/src/cpu/pred/BranchPredictor.py
index 2c622cd02..0c1e9c284 100644
--- a/src/cpu/pred/BranchPredictor.py
+++ b/src/cpu/pred/BranchPredictor.py
@@ -143,3 +143,19 @@ class LTAGE(TAGE):
     loopTableIterBits = Param.Unsigned(14, "Nuber of iteration bits per loop")
     logLoopTableAssoc = Param.Unsigned(2, "Log loop predictor associativity")
 
+    # Parameters for enabling modifications to the loop predictor
+    # They have been copied from ISL-TAGE
+    # (https://www.jilp.org/jwac-2/program/03_seznec.tgz)
+    #
+    # All of them should be disabled to match the original LTAGE implementation
+    # (http://hpca23.cse.tamu.edu/taco/camino/cbp2/cbp-src/realistic-seznec.h)
+
+    # Add speculation
+    useSpeculation = Param.Bool(False, "Use speculation")
+
+    # Add hashing for calculating the loop table index
+    useHashing = Param.Bool(False, "Use hashing")
+
+    # Add a direction bit to the loop table entries
+    useDirectionBit = Param.Bool(False, "Use direction info")
+