From: Geoffrey Blake <geoffrey.blake@arm.com>
Date: Fri, 15 Feb 2013 22:40:10 +0000 (-0500)
Subject: cpu: Avoid duplicate entries in tracking structures for writes to misc regs
X-Git-Tag: stable_2013_06_16~111
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=ca96e7bff1dfaa8e0a6d900feb88c711198b4b2b;p=gem5.git

cpu: Avoid duplicate entries in tracking structures for writes to misc regs

setMiscReg currently makes a new entry for each write to a misc reg without
checking for duplicates, this can cause a triggering of the assert if an
instruction get replayed and writes to the same misc regs multiple times.
This fix prevents duplicate entries and instead updates the value.
---

diff --git a/src/cpu/o3/dyn_inst.hh b/src/cpu/o3/dyn_inst.hh
index c8cdf7a1f..082c1f5d4 100644
--- a/src/cpu/o3/dyn_inst.hh
+++ b/src/cpu/o3/dyn_inst.hh
@@ -149,8 +149,18 @@ class BaseO3DynInst : public BaseDynInst<Impl>
     void setMiscReg(int misc_reg, const MiscReg &val)
     {
         /** Writes to misc. registers are recorded and deferred until the
-         * commit stage, when updateMiscRegs() is called.
+         * commit stage, when updateMiscRegs() is called. First, check if
+         * the misc reg has been written before and update its value to be
+         * committed instead of making a new entry. If not, make a new
+         * entry and record the write.
          */
+        for (int idx = 0; idx < _numDestMiscRegs; idx++) {
+            if (_destMiscRegIdx[idx] == misc_reg) {
+               _destMiscRegVal[idx] = val;
+               return;
+            }
+        }
+
         assert(_numDestMiscRegs < TheISA::MaxMiscDestRegs);
         _destMiscRegIdx[_numDestMiscRegs] = misc_reg;
         _destMiscRegVal[_numDestMiscRegs] = val;