Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -11459,20 +11459,7 @@
     // The positive stride case is the same as isKnownPositive(Stride) returning
     // true (original behavior of the function).
     //
-    // We want to make sure that the stride is truly unknown as there are edge
-    // cases where ScalarEvolution propagates no wrap flags to the
-    // post-increment/decrement IV even though the increment/decrement operation
-    // itself is wrapping. The computed backedge taken count may be wrong in
-    // such cases. This is prevented by checking that the stride is not known to
-    // be either positive or non-positive. For example, no wrap flags are
-    // propagated to the post-increment IV of this loop with a trip count of 2 -
-    //
-    // unsigned char i;
-    // for(i=127; i<128; i+=129)
-    //   A[i] = i;
-    //
-    if (PredicatedIV || !NoWrap || isKnownNonPositive(Stride) ||
-        !loopIsFiniteByAssumption(L))
+    if (PredicatedIV || !NoWrap || !loopIsFiniteByAssumption(L))
       return getCouldNotCompute();
   } else if (!Stride->isOne() && !NoWrap) {
     auto isUBOnWrap = [&]() {
Index: llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll
+++ llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll
@@ -106,5 +106,45 @@
   ret void
 }
 
+; In this example, we branch on poison on the first iteration, so the
+; loop is undefined, and thus any answer is valid.
+; CHECK: Determining loop execution counts for: @foo5
+; CHECK: Loop %for.body: backedge-taken count is 1
+; CHECK: Loop %for.body: max backedge-taken count is 1
+
+define void @foo5(i32* nocapture %A, i32 %n, i32 %s) {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  %i.05 = phi i8 [ %add, %for.body ], [ 127, %entry ]
+  %add = add nsw nuw i8 %i.05, 129
+  %cmp = icmp ult i8 %add, 128
+  br i1 %cmp, label %for.body, label %for.end, !llvm.loop !8
+
+for.end:                                          ; preds = %for.body, %entry
+  ret void
+}
+
+; Defined version of foo5, in this case 1 is the correct answer
+; CHECK: Determining loop execution counts for: @foo6
+; CHECK: Loop %for.body: backedge-taken count is 1
+; CHECK: Loop %for.body: max backedge-taken count is 1
+
+define void @foo6(i32* nocapture %A, i32 %n, i32 %s) {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  %i.05 = phi i8 [ %add, %for.body ], [ 127, %entry ]
+  %add = add nsw nuw i8 %i.05, 129
+  %cmp = icmp ult i8 %add, 128
+  br i1 %cmp, label %for.body, label %for.end, !llvm.loop !8
+
+for.end:                                          ; preds = %for.body, %entry
+  ret void
+}
+
+
 !8 = distinct !{!8, !9}
 !9 = !{!"llvm.loop.mustprogress"}