[ValueTracking] remove a FIXME for something we don't want to do; NFC

The comment was added with:
https://reviews.llvm.org/rL293773
...but there would be a cost to implement this and possibly no payoff.

llvm-svn: 293823

llvm/lib/Analysis/ValueTracking.cpp

@@ -797,10 +797,6 @@ static void computeKnownBitsFromAssume(const Value *V, APInt &KnownZero,
   // FIXME: Publish a warning/remark that we have encountered UB or the compiler
   // is broken.
 
-  // FIXME: Implement a stronger version of "I give up" by invalidating/clearing
-  // the assumption cache. This should indicate that the cache is corrupted so
-  // future callers will not waste time repopulating it with faulty assumptions.
-
   if ((KnownZero & KnownOne) != 0) {
     KnownZero.clearAllBits();
     KnownOne.clearAllBits();

llvm/test/Transforms/InstSimplify/assume.ll

@@ -28,8 +28,7 @@ define i64 @PR31809() {
 
 ; Similar to above: there's no way to know which assumption is truthful,
 ; so just don't crash. The second icmp+assume gets processed later, so that
-; determines the return value. This can be improved by permanently invalidating
-; the cached assumptions for this function. 
+; determines the return value.
 
 define i8 @conflicting_assumptions(i8 %x) {
 ; CHECK-LABEL: @conflicting_assumptions(