[SCEV][NFC] Introduce isBasicBlockEntryGuardedByCond

Currently, we have `isLoopEntryGuardedByCond` method in SCEV, which
checks that some fact is true if we enter the loop. In fact, this is just a
particular case of more general concept `isBasicBlockEntryGuardedByCond`
applied to given loop's header. In fact, the logic if this code is largely
independent on the given loop and only cares code above it.

This patch makes this generalization. Now we can query it for any block,
and `isBasicBlockEntryGuardedByCond` is just a particular case.

Differential Revision: https://reviews.llvm.org/D87828
Reviewed By: fhahn

llvm/include/llvm/Analysis/ScalarEvolution.h

@@ -677,6 +677,12 @@ public:
   bool isLoopEntryGuardedByCond(const Loop *L, ICmpInst::Predicate Pred,
                                 const SCEV *LHS, const SCEV *RHS);
 
+  /// Test whether entry to the basic block is protected by a conditional
+  /// between LHS and RHS.
+  bool isBasicBlockEntryGuardedByCond(const BasicBlock *BB,
+                                      ICmpInst::Predicate Pred, const SCEV *LHS,
+                                      const SCEV *RHS);
+
   /// Test whether the backedge of the loop is protected by a conditional
   /// between LHS and RHS.  This is used to eliminate casts.
   bool isLoopBackedgeGuardedByCond(const Loop *L, ICmpInst::Predicate Pred,

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -9492,24 +9492,14 @@ ScalarEvolution::isLoopBackedgeGuardedByCond(const Loop *L,
   return false;
 }
 
-bool
-ScalarEvolution::isLoopEntryGuardedByCond(const Loop *L,
-                                          ICmpInst::Predicate Pred,
-                                          const SCEV *LHS, const SCEV *RHS) {
-  // Interpret a null as meaning no loop, where there is obviously no guard
-  // (interprocedural conditions notwithstanding).
-  if (!L) return false;
-
+bool ScalarEvolution::isBasicBlockEntryGuardedByCond(const BasicBlock *BB,
+                                                     ICmpInst::Predicate Pred,
+                                                     const SCEV *LHS,
+                                                     const SCEV *RHS) {
   if (VerifyIR)
-    assert(!verifyFunction(*L->getHeader()->getParent(), &dbgs()) &&
+    assert(!verifyFunction(*BB->getParent(), &dbgs()) &&
            "This cannot be done on broken IR!");
 
-  // Both LHS and RHS must be available at loop entry.
-  assert(isAvailableAtLoopEntry(LHS, L) &&
-         "LHS is not available at Loop Entry");
-  assert(isAvailableAtLoopEntry(RHS, L) &&
-         "RHS is not available at Loop Entry");
-
   if (isKnownViaNonRecursiveReasoning(Pred, LHS, RHS))
     return true;
 
@@ -9566,13 +9556,17 @@ ScalarEvolution::isLoopEntryGuardedByCond(const Loop *L,
     return false;
   };
 
-  // Starting at the loop predecessor, climb up the predecessor chain, as long
+  // Starting at the block's predecessor, climb up the predecessor chain, as long
   // as there are predecessors that can be found that have unique successors
-  // leading to the original header.
-  for (std::pair<const BasicBlock *, const BasicBlock *> Pair(
-           L->getLoopPredecessor(), L->getHeader());
+  // leading to the original block.
+  const Loop *ContainingLoop = LI.getLoopFor(BB);
+  const BasicBlock *PredBB;
+  if (ContainingLoop && ContainingLoop->getHeader() == BB)
+    PredBB = ContainingLoop->getLoopPredecessor();
+  else
+    PredBB = BB->getSinglePredecessor();
+  for (std::pair<const BasicBlock *, const BasicBlock *> Pair(PredBB, BB);
        Pair.first; Pair = getPredecessorWithUniqueSuccessorForBB(Pair.first)) {
-
     if (ProveViaGuard(Pair.first))
       return true;
 
@@ -9592,7 +9586,7 @@ ScalarEvolution::isLoopEntryGuardedByCond(const Loop *L,
     if (!AssumeVH)
       continue;
     auto *CI = cast<CallInst>(AssumeVH);
-    if (!DT.dominates(CI, L->getHeader()))
+    if (!DT.dominates(CI, BB))
       continue;
 
     if (ProveViaCond(CI->getArgOperand(0), false))
@@ -9602,6 +9596,23 @@ ScalarEvolution::isLoopEntryGuardedByCond(const Loop *L,
   return false;
 }
 
+bool ScalarEvolution::isLoopEntryGuardedByCond(const Loop *L,
+                                               ICmpInst::Predicate Pred,
+                                               const SCEV *LHS,
+                                               const SCEV *RHS) {
+  // Interpret a null as meaning no loop, where there is obviously no guard
+  // (interprocedural conditions notwithstanding).
+  if (!L)
+    return false;
+
+  // Both LHS and RHS must be available at loop entry.
+  assert(isAvailableAtLoopEntry(LHS, L) &&
+         "LHS is not available at Loop Entry");
+  assert(isAvailableAtLoopEntry(RHS, L) &&
+         "RHS is not available at Loop Entry");
+  return isBasicBlockEntryGuardedByCond(L->getHeader(), Pred, LHS, RHS);
+}
+
 bool ScalarEvolution::isImpliedCond(ICmpInst::Predicate Pred, const SCEV *LHS,
                                     const SCEV *RHS,
                                     const Value *FoundCondValue, bool Inverse) {