mem, cpu: Add assertions to snoop invalidation logic

This patch adds assertions that enforce that only invalidating snoops
will ever reach into the logic that tracks in-order load completion and
also invalidation of LL/SC (and MONITOR / MWAIT) monitors. Also adds
some comments to MSHR::replaceUpgrades().

src/arch/arm/locked_mem.hh

@@ -64,7 +64,10 @@ template <class XC>
 inline void
 handleLockedSnoop(XC *xc, PacketPtr pkt, Addr cacheBlockMask)
 {
-    DPRINTF(LLSC,"%s:  handleing snoop for address: %#x locked: %d\n",
+    // Should only every see invalidations / direct writes
+    assert(pkt->isInvalidate() || pkt->isWrite());
+
+    DPRINTF(LLSC,"%s:  handling snoop for address: %#x locked: %d\n",
             xc->getCpuPtr()->name(),pkt->getAddr(),
             xc->readMiscReg(MISCREG_LOCKFLAG));
     if (!xc->readMiscReg(MISCREG_LOCKFLAG))
@@ -74,7 +77,7 @@ handleLockedSnoop(XC *xc, PacketPtr pkt, Addr cacheBlockMask)
     // If no caches are attached, the snoop address always needs to be masked
     Addr snoop_addr = pkt->getAddr() & cacheBlockMask;
 
-    DPRINTF(LLSC,"%s:  handleing snoop for address: %#x locked addr: %#x\n",
+    DPRINTF(LLSC,"%s:  handling snoop for address: %#x locked addr: %#x\n",
             xc->getCpuPtr()->name(),snoop_addr, locked_addr);
     if (locked_addr == snoop_addr) {
         DPRINTF(LLSC,"%s: address match, clearing lock and signaling sev\n",

src/cpu/o3/lsq_unit_impl.hh

@@ -435,6 +435,9 @@ template <class Impl>
 void
 LSQUnit<Impl>::checkSnoop(PacketPtr pkt)
 {
+    // Should only ever get invalidations in here
+    assert(pkt->isInvalidate());
+
     int load_idx = loadHead;
     DPRINTF(LSQUnit, "Got snoop for address %#x\n", pkt->getAddr());
 

src/mem/cache/blk.hh

@@ -335,6 +335,8 @@ class CacheBlk
      */
     bool checkWrite(PacketPtr pkt)
     {
+        assert(pkt->isWrite());
+
         // common case
         if (!pkt->isLLSC() && lockList.empty())
             return true;

src/mem/cache/mshr.hh

@@ -149,7 +149,13 @@ class MSHR : public Packet::SenderState, public Printable
         bool isReset() const { return !needsWritable && !hasUpgrade; }
         void add(PacketPtr pkt, Tick readyTime, Counter order,
                  Target::Source source, bool markPending);
+
+        /**
+         * Convert upgrades to the equivalent request if the cache line they
+         * refer to would have been invalid (Upgrade -> ReadEx, SC* -> Fail).
+         * Used to rejig ordering between targets waiting on an MSHR. */
         void replaceUpgrades();
+
         void clearDownstreamPending();
         bool checkFunctional(PacketPtr pkt);
         void print(std::ostream &os, int verbosity,