O3: Support squashing all state after special instruction

For SPARC ASIs are added to the ExtMachInst. If the ASI is changed simply
marking the instruction as Serializing isn't enough beacuse that only
stops rename. This provides a mechanism to squash all the instructions
and refetch them

src/arch/sparc/isa/decoder.isa

@@ -490,7 +490,8 @@ decode OP default Unknown::unknown()
                 0x00: NoPriv::wry({{Y = (Rs1 ^ Rs2_or_imm13)<31:0>;}});
                 // 0x01 should cause an illegal instruction exception
                 0x02: NoPriv::wrccr({{Ccr = Rs1 ^ Rs2_or_imm13;}});
-                0x03: NoPriv::wrasi({{Asi = Rs1 ^ Rs2_or_imm13;}});
+                0x03: NoPriv::wrasi({{Asi = Rs1 ^ Rs2_or_imm13;}}, false,
+                                    IsSquashAfter);
                 // 0x04-0x05 should cause an illegal instruction exception
                 0x06: NoPriv::wrfprs({{Fprs = Rs1 ^ Rs2_or_imm13;}});
                 // 0x07-0x0E should cause an illegal instruction exception

src/cpu/base_dyn_inst.hh

@@ -478,6 +478,7 @@ class BaseDynInst : public FastAlloc, public RefCounted
     { return staticInst->isSerializeBefore() || status[SerializeBefore]; }
     bool isSerializeAfter() const
     { return staticInst->isSerializeAfter() || status[SerializeAfter]; }
+    bool isSquashAfter() const { return staticInst->isSquashAfter(); }
     bool isMemBarrier()   const { return staticInst->isMemBarrier(); }
     bool isWriteBarrier() const { return staticInst->isWriteBarrier(); }
     bool isNonSpeculative() const { return staticInst->isNonSpeculative(); }

src/cpu/o3/commit.hh

@@ -245,6 +245,13 @@ class DefaultCommit
     /** Handles squashing due to an TC write. */
     void squashFromTC(ThreadID tid);
 
+    /** Handles squashing from instruction with SquashAfter set.
+     * This differs from the other squashes as it squashes following
+     * instructions instead of the current instruction and doesn't
+     * clean up various status bits about traps/tc writes pending.
+     */
+    void squashAfter(ThreadID tid, uint64_t squash_after_seq_num);
+
 #if FULL_SYSTEM
     /** Handles processing an interrupt. */
     void handleInterrupt();

src/cpu/o3/commit_impl.hh

@@ -559,6 +559,33 @@ DefaultCommit<Impl>::squashFromTC(ThreadID tid)
     tcSquash[tid] = false;
 }
 
+template <class Impl>
+void
+DefaultCommit<Impl>::squashAfter(ThreadID tid, uint64_t squash_after_seq_num)
+{
+    youngestSeqNum[tid] = squash_after_seq_num;
+
+    rob->squash(squash_after_seq_num, tid);
+    changedROBNumEntries[tid] = true;
+
+    // Send back the sequence number of the squashed instruction.
+    toIEW->commitInfo[tid].doneSeqNum = squash_after_seq_num;
+
+    // Send back the squash signal to tell stages that they should squash.
+    toIEW->commitInfo[tid].squash = true;
+
+    // Send back the rob squashing signal so other stages know that
+    // the ROB is in the process of squashing.
+    toIEW->commitInfo[tid].robSquashing = true;
+
+    toIEW->commitInfo[tid].branchMispredict = false;
+
+    toIEW->commitInfo[tid].pc = pc[tid];
+    DPRINTF(Commit, "Executing squash after for [tid:%i] inst [sn:%lli]\n",
+            tid, squash_after_seq_num);
+    commitStatus[tid] = ROBSquashing;
+}
+
 template <class Impl>
 void
 DefaultCommit<Impl>::tick()
@@ -917,6 +944,11 @@ DefaultCommit<Impl>::commitInsts()
 
                 TheISA::advancePC(pc[tid], head_inst->staticInst);
 
+                // If this is an instruction that doesn't play nicely with
+                // others squash everything and restart fetch
+                if (head_inst->isSquashAfter())
+                    squashAfter(tid, head_inst->seqNum);
+
                 int count = 0;
                 Addr oldpc;
                 // Debug statement.  Checks to make sure we're not

src/cpu/static_inst.hh

@@ -158,7 +158,7 @@ class StaticInstBase : public RefCounted
         //This flag doesn't do anything yet
         IsMicroBranch,  ///< This microop branches within the microcode for a macroop
         IsDspOp,
-
+        IsSquashAfter, ///< Squash all uncommitted state after executed
         NumFlags
     };
 
@@ -248,6 +248,7 @@ class StaticInstBase : public RefCounted
                                       flags[IsSerializeAfter]; }
     bool isSerializeBefore() const { return flags[IsSerializeBefore]; }
     bool isSerializeAfter() const { return flags[IsSerializeAfter]; }
+    bool isSquashAfter() const { return flags[IsSquashAfter]; }
     bool isMemBarrier()   const { return flags[IsMemBarrier]; }
     bool isWriteBarrier() const { return flags[IsWriteBarrier]; }
     bool isNonSpeculative() const { return flags[IsNonSpeculative]; }