pred: support DecoupledBPUWithBTB

- Add support for DecoupledBPUWithBTB in xiangshan.py configuration
- Disable loop predictor, loop buffer, and jump ahead predictor for DecoupledBPUWithBTB
- Add enableSC parameter to BTBTAGE branch predictor

.gitignore

@@ -48,4 +48,6 @@ llvm-pgo/
 *.profraw
 *nemu*
 ready-to-run/
-*.out
+*.out
+.cursorrules
+.cursorignore

configs/example/xiangshan.py

@@ -113,15 +113,25 @@ def build_test_system(np, args):
         args.enable_loop_buffer = True
 
     for i in range(np):
-        if args.bp_type is None or args.bp_type == 'DecoupledBPUWithFTB':
+        if args.bp_type is None or args.bp_type == 'DecoupledBPUWithFTB' or args.bp_type == 'DecoupledBPUWithBTB':
             enable_bp_db = len(args.enable_bp_db) > 1
             if enable_bp_db:
                 bp_db_switches = args.enable_bp_db[1] + ['basic']
                 print("BP db switches:", bp_db_switches)
             else:
                 bp_db_switches = []
-
-            test_sys.cpu[i].branchPred = DecoupledBPUWithFTB(
+            # for DecoupledBPUWithBTB, loop predictor and jump ahead predictor are not supported
+            if args.bp_type == 'DecoupledBPUWithBTB':
+                if args.enable_loop_predictor or args.enable_loop_buffer:
+                    print("loop predictor and loop buffer not supported for DecoupledBPUWithBTB")
+                    args.enable_loop_predictor = False
+                    args.enable_loop_buffer = False
+                if args.enable_jump_ahead_predictor:
+                    print("jump ahead predictor not supported for DecoupledBPUWithBTB")
+                    args.enable_jump_ahead_predictor = False
+
+            BPClass = DecoupledBPUWithBTB() if args.bp_type == 'DecoupledBPUWithBTB' else DecoupledBPUWithFTB()
+            test_sys.cpu[i].branchPred = BPClass(
                                             bpDBSwitches=bp_db_switches,
                                             enableLoopBuffer=args.enable_loop_buffer,
                                             enableLoopPredictor=args.enable_loop_predictor,

src/cpu/pred/BranchPredictor.py

@@ -999,6 +999,7 @@ class BTBTAGE(TimedBaseBTBPredictor):
     cxx_class = 'gem5::branch_prediction::btb_pred::BTBTAGE'
     cxx_header = "cpu/pred/btb/btb_tage.hh"
 
+    enableSC = Param.Bool(False, "Enable SC or not")    # TODO: BTBTAGE doesn't support SC
     numPredictors = Param.Unsigned(4, "Number of TAGE predictors")
     tableSizes = VectorParam.Unsigned([4096]*4, "the ITTAGE T0~Tn length")
     TTagBitSizes = VectorParam.Unsigned([8]*4, "the T0~Tn entry's tag bit size")

src/cpu/pred/btb/btb_tage.cc

@@ -26,6 +26,7 @@ tablePcShifts(p.TTagPcShifts),
 histLengths(p.histLengths),
 maxHistLen(p.maxHistLen),
 numTablesToAlloc(p.numTablesToAlloc),
+enableSC(p.enableSC),
 tageStats(this, p.numPredictors)
 {
     DPRINTF(TAGE, "BTBTAGE constructor\n");