Fixing LoopBuffer bug

.jenkins/build_test_run.sh

@@ -71,7 +71,7 @@ run () {
     cat run
     echo ""
     compare_outputs "$(grep "retired:" run | rev | cut -d ' ' -f1 | rev)" "6724" "retired instructions"
-    compare_outputs "$(grep "cycles:" run | rev | cut -d ' ' -f1 | rev)" "8677" "simulated cycles"
+    compare_outputs "$(grep "cycles:" run | rev | cut -d ' ' -f1 | rev)" "8612" "simulated cycles"
     echo ""
 }
 

src/include/simeng/Instruction.hh

@@ -157,7 +157,7 @@ class Instruction {
     // Flag as mispredicted if taken state was wrongly predicted, or taken and
     // predicted target is wrong
     return (branchTaken_ != prediction_.taken ||
-            (prediction_.target != branchAddress_));
+            (branchTaken_ && (prediction_.target != branchAddress_)));
   }
 
   /** Check whether an exception has been encountered while processing this

src/lib/pipeline/FetchUnit.cc

@@ -176,8 +176,17 @@ void FetchUnit::tick() {
       }
     } else if (loopBufferState_ == LoopBufferState::WAITING &&
                pc_ == loopBoundaryAddress_) {
-      // Once set loopBoundaryAddress_ is fetched, start to fill loop buffer
-      loopBufferState_ = LoopBufferState::FILLING;
+      // loopBoundaryAddress_ has been fetched whilst loop buffer is waiting,
+      // start filling Loop Buffer if the branch predictor tells us to
+      // reenter the detected loop
+      if (macroOp[0]->isBranch() && !macroOp[0]->getBranchPrediction().taken) {
+        // If branch is not taken then we aren't re-entering the detected
+        // loop, therefore Loop Buffer stays idle
+        loopBufferState_ = LoopBufferState::IDLE;
+      } else {
+        // Otherwise, start to fill Loop Buffer
+        loopBufferState_ = LoopBufferState::FILLING;
+      }
     }
 
     assert(bytesRead <= bufferedBytes_ &&