diff --git a/js/src/nanojit/LIR.cpp b/js/src/nanojit/LIR.cpp
index 523eadffca98..e30978ff5f24 100644
--- a/js/src/nanojit/LIR.cpp
+++ b/js/src/nanojit/LIR.cpp
@@ -1959,7 +1959,6 @@ namespace nanojit
           CSE_ACC_MULTIPLE( EMB_NUM_USED_ACCS + 1),
           storesSinceLastLoad(ACCSET_NONE),
           alloc(alloc),
-          knownCmpValues(alloc),
           suspended(false)
     {
 
@@ -2061,8 +2060,6 @@ namespace nanojit
         // Note that this clears the CONST and MULTIPLE load tables as well.
         for (CseAcc a = 0; a < CSE_NUM_USED_ACCS; a++)
             clearL(a);
-
-        knownCmpValues.clear();
     }
 
     inline uint32_t CseFilter::hashImmI(int32_t a) {
@@ -2466,15 +2463,6 @@ namespace nanojit
         if (!ins) {
             ins = out->ins2(op, a, b);
             addNL(LIns2, ins, k);
-        } else if (ins->isCmp()) {
-            if (knownCmpValues.containsKey(ins)) {
-                // We've seen this comparison before, and it was previously
-                // used in a guard, so we know what its value must be at this
-                // point.  Replace it with a constant.
-                NanoAssert(ins->isCmp());
-                bool cmpValue = knownCmpValues.get(ins);
-                return insImmI(cmpValue ? 1 : 0);
-            }
         }
         NanoAssert(ins->isop(op) && ins->oprnd1() == a && ins->oprnd2() == b);
         return ins;
@@ -2589,13 +2577,6 @@ namespace nanojit
                 ins = out->insGuard(op, c, gr);
                 addNL(LIns1, ins, k);
             }
-            // After this guard, we know that 'c's result was true (if
-            // op==LIR_xf) or false (if op==LIR_xt), else we would have
-            // exited.  Record this fact in case 'c' occurs again.
-            if (!suspended) {
-                bool c_value = (op == LIR_xt ? false : true);
-                knownCmpValues.put(c, c_value);
-            }
         } else {
             ins = out->insGuard(op, c, gr);
         }
diff --git a/js/src/nanojit/LIR.h b/js/src/nanojit/LIR.h
index 01e6b2ce8d09..fa5924a11ac2 100644
--- a/js/src/nanojit/LIR.h
+++ b/js/src/nanojit/LIR.h
@@ -1964,12 +1964,6 @@ namespace nanojit
 
         Allocator& alloc;
 
-        // After a conditional guard such as "xf cmp", we know that 'cmp' must
-        // be true, else we would have side-exited.  So if we see 'cmp' again
-        // we can treat it like a constant.  This table records such
-        // comparisons.
-        HashMap <LIns*, bool> knownCmpValues;
-
         // If true, we will not add new instructions to the CSE tables, but we
         // will continue to CSE instructions that match existing table
         // entries.  Load instructions will still be removed if aliasing