Index: lib/Analysis/DependenceAnalysis.cpp
===================================================================
--- lib/Analysis/DependenceAnalysis.cpp
+++ lib/Analysis/DependenceAnalysis.cpp
@@ -948,7 +948,7 @@
                                                   Type *T) const {
   if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
     const SCEV *UB = SE->getBackedgeTakenCount(L);
-    return SE->getNoopOrZeroExtend(UB, T);
+    return SE->getTruncateOrZeroExtend(UB, T);
   }
   return nullptr;
 }
Index: test/Analysis/DependenceAnalysis/PR21585.ll
===================================================================
--- /dev/null
+++ test/Analysis/DependenceAnalysis/PR21585.ll
@@ -0,0 +1,21 @@
+; RUN: opt < %s -analyze -basicaa -da
+
+define void @i32_subscript(i32* %a) {
+entry:
+  br label %for.body
+
+for.body:
+  %i = phi i32 [ 0, %entry ], [ %i.inc, %for.body ]
+  %a.addr = getelementptr i32, i32* %a, i32 %i
+  %a.addr.2 = getelementptr i32, i32* %a, i32 5
+  %0 = load i32, i32* %a.addr, align 4
+  %1 = add i32 %0, 1
+  store i32 %1, i32* %a.addr.2, align 4
+  %i.inc = add nsw i32 %i, 1
+  %i.inc.ext = sext i32 %i to i64
+  %exitcond = icmp ne i64 %i.inc.ext, 100
+  br i1 %exitcond, label %for.body, label %for.end
+
+for.end:
+  ret void
+}