cpu-o3: Fixed halt assertion failure

Halting the O3 CPU would cause an assertion failure because
instructions were not finished being squashed in the ROB.

Change-Id: I8b8c375d0e520861af3657249de987de2451b6f1
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/37676
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

src/cpu/o3/cpu.cc

@@ -717,6 +717,15 @@ FullO3CPU<Impl>::haltContext(ThreadID tid)
     deactivateThread(tid);
     removeThread(tid);
 
+    // If this was the last thread then unschedule the tick event.
+    if (activeThreads.size() == 0) {
+        if (tickEvent.scheduled())
+        {
+            unscheduleTickEvent();
+        }
+        lastRunningCycle = curCycle();
+        _status = Idle;
+    }
     updateCycleCounters(BaseCPU::CPU_STATE_SLEEP);
 }
 
@@ -795,6 +804,15 @@ FullO3CPU<Impl>::removeThread(ThreadID tid)
     rename.clearStates(tid);
     iew.clearStates(tid);
 
+    // Flush out any old data from the time buffers.
+    for (int i = 0; i < timeBuffer.getSize(); ++i) {
+        timeBuffer.advance();
+        fetchQueue.advance();
+        decodeQueue.advance();
+        renameQueue.advance();
+        iewQueue.advance();
+    }
+
     // at this step, all instructions in the pipeline should be already
     // either committed successfully or squashed. All thread-specific
     // queues in the pipeline must be empty.

src/cpu/o3/rob_impl.hh

@@ -338,8 +338,18 @@ ROB<Impl>::doSquash(ThreadID tid)
 
     bool robTailUpdate = false;
 
+    unsigned int numInstsToSquash = squashWidth;
+
+    // If the CPU is exiting, squash all of the instructions
+    // it is told to, even if that exceeds the squashWidth.
+    // Set the number to the number of entries (the max).
+    if (cpu->isThreadExiting(tid))
+    {
+        numInstsToSquash = numEntries;
+    }
+
     for (int numSquashed = 0;
-         numSquashed < squashWidth &&
+         numSquashed < numInstsToSquash &&
          squashIt[tid] != instList[tid].end() &&
          (*squashIt[tid])->seqNum > squashedSeqNum[tid];
          ++numSquashed)