[SCEV] Move assumes checks into isKnownPredicateAt

[mkazantsev]

Summary

We can benefit from assumes in isKnownPredicateAt, not only in
isLoopBackedgeGuardedByCond. The proof there also may become
more powerful from using the context.

[mkazantsev]

Already present in isBasicBlockEntryGuardedByCond.

llvm/lib/Analysis/ScalarEvolution.cpp

bool ScalarEvolution::isKnownPredicate(ICmpInst::Predicate Pred,
 
   // Otherwise see what can be done with some simple reasoning.
   return isKnownViaNonRecursiveReasoning(Pred, LHS, RHS);
 }
 
 bool ScalarEvolution::isKnownPredicateAt(ICmpInst::Predicate Pred,
                                          const SCEV *LHS, const SCEV *RHS,
                                          const Instruction *Context) {
-  // TODO: Analyze guards and assumes from Context's block.
+  // Check conditions due to any @llvm.assume intrinsics.
+  for (auto &AssumeVH : AC.assumptions()) {
+    if (!AssumeVH)
+      continue;
+    auto *CI = cast<CallInst>(AssumeVH);
+    if (!DT.dominates(CI, Context))
+      continue;
+
+    if (isImpliedCond(Pred, LHS, RHS, CI->getArgOperand(0), false, Context))
+      return true;
+  }
+
   return isKnownPredicate(Pred, LHS, RHS) ||
          isBasicBlockEntryGuardedByCond(Context->getParent(), Pred, LHS, RHS);
 }
 
 bool ScalarEvolution::isKnownOnEveryIteration(ICmpInst::Predicate Pred,
                                               const SCEVAddRecExpr *LHS,
                                               const SCEV *RHS) {
   const Loop *L = LHS->getLoop();
if (LatchBECount != getCouldNotCompute()) {
     auto NoWrapFlags = SCEV::NoWrapFlags(SCEV::FlagNUW | SCEV::FlagNW);
     const SCEV *LoopCounter =
       getAddRecExpr(getZero(Ty), getOne(Ty), L, NoWrapFlags);
     if (isImpliedCond(Pred, LHS, RHS, ICmpInst::ICMP_ULT, LoopCounter,
                       LatchBECount))
       return true;
   }
 
-  // Check conditions due to any @llvm.assume intrinsics.
-  for (auto &AssumeVH : AC.assumptions()) {
-    if (!AssumeVH)
-      continue;
-    auto *CI = cast<CallInst>(AssumeVH);
-    if (!DT.dominates(CI, Latch->getTerminator()))
-      continue;
-
-    if (isImpliedCond(Pred, LHS, RHS, CI->getArgOperand(0), false))
-      return true;
-  }
-
   // If the loop is not reachable from the entry block, we risk running into an
   // infinite loop as we walk up into the dom tree.  These loops do not matter
   // anyway, so we just return a conservative answer when we see them.
   if (!DT.isReachableFromEntry(L->getHeader()))
     return false;
 
   if (isImpliedViaGuard(Latch, Pred, LHS, RHS))
     return true;