[SCEV] Use isKnownPredicateAt in isLoopBackedgeGuardedByCond

A piece of code in `isLoopBackedgeGuardedByCond` basically duplicates
the dominators traversal from `isBlockEntryGuardedByCond` called from
`isKnownPredicateAt`, but it's less powerful because it does not give context
to `isImpliedCond`. This patch reuses the `isKnownPredicateAt `function there,
reducing the amount of code duplication and making it more powerful.

Differential Revision: https://reviews.llvm.org/D92152
Reviewed By: skatkov

2 files changed, 2 insertions, 37 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 53fd668..31b88c9 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -9911,42 +9911,7 @@ ScalarEvolution::isLoopBackedgeGuardedByCond(const Loop *L,
   if (isImpliedViaGuard(Latch, Pred, LHS, RHS))
     return true;
 
-  for (DomTreeNode *DTN = DT[Latch], *HeaderDTN = DT[L->getHeader()];
-       DTN != HeaderDTN; DTN = DTN->getIDom()) {
-    assert(DTN && "should reach the loop header before reaching the root!");
-
-    BasicBlock *BB = DTN->getBlock();
-    if (isImpliedViaGuard(BB, Pred, LHS, RHS))
-      return true;
-
-    BasicBlock *PBB = BB->getSinglePredecessor();
-    if (!PBB)
-      continue;
-
-    BranchInst *ContinuePredicate = dyn_cast<BranchInst>(PBB->getTerminator());
-    if (!ContinuePredicate || !ContinuePredicate->isConditional())
-      continue;
-
-    Value *Condition = ContinuePredicate->getCondition();
-
-    // If we have an edge `E` within the loop body that dominates the only
-    // latch, the condition guarding `E` also guards the backedge.  This
-    // reasoning works only for loops with a single latch.
-
-    BasicBlockEdge DominatingEdge(PBB, BB);
-    if (DominatingEdge.isSingleEdge()) {
-      // We're constructively (and conservatively) enumerating edges within the
-      // loop body that dominate the latch.  The dominator tree better agree
-      // with us on this:
-      assert(DT.dominates(DominatingEdge, Latch) && "should be!");
-
-      if (isImpliedCond(Pred, LHS, RHS, Condition,
-                        BB != ContinuePredicate->getSuccessor(0)))
-        return true;
-    }
-  }
-
-  return false;
+  return isKnownPredicateAt(Pred, LHS, RHS, Latch->getTerminator());
 }
 
 bool ScalarEvolution::isBasicBlockEntryGuardedByCond(const BasicBlock *BB,
diff --git a/llvm/test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll b/llvm/test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll
index 8a07a49..c398289 100644
--- a/llvm/test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll
+++ b/llvm/test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll
@@ -69,7 +69,7 @@ define void @_Z15IntegerToStringjjR7Vector2(i32 %i, i32 %radix, %struct.Vector2*
 ; CHECK-NEXT:    [[UGLYGEP2:%.*]] = bitcast i8* [[UGLYGEP]] to i16*
 ; CHECK-NEXT:    [[TMP29:%.*]] = load i16, i16* [[LSR_IV810]], align 2
 ; CHECK-NEXT:    store i16 [[TMP29]], i16* [[UGLYGEP2]], align 2
-; CHECK-NEXT:    [[LSR_IV_NEXT]] = add i64 [[LSR_IV]], 2
+; CHECK-NEXT:    [[LSR_IV_NEXT]] = add nuw nsw i64 [[LSR_IV]], 2
 ; CHECK-NEXT:    [[LSR_IV_NEXT3:%.*]] = inttoptr i64 [[LSR_IV_NEXT]] to i16*
 ; CHECK-NEXT:    [[SCEVGEP9:%.*]] = getelementptr [33 x i16], [33 x i16]* [[LSR_IV8]], i64 0, i64 1
 ; CHECK-NEXT:    [[TMP3]] = bitcast i16* [[SCEVGEP9]] to [33 x i16]*