[PATCH] D109029: [SCEV] Clarify requirements for zero-stride to be UB

[Philip Reames via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rG73b951a7f7dc: [SCEV] Clarify requirements for zero-stride to be UB (authored by reames).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D109029/new/

https://reviews.llvm.org/D109029

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp


Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -11633,13 +11633,15 @@
     // a) IV is either nuw or nsw depending upon signedness (indicated by the
     //    NoWrap flag).
     // b) loop is single exit with no side effects.
+    // c) loop has no abnormal exits
     //
     //
     // Precondition a) implies that if the stride is negative, this is a single
     // trip loop. The backedge taken count formula reduces to zero in this case.
     //
-    // Precondition b) implies that if rhs is invariant in L, then unknown
-    // stride being zero means the backedge can't be taken without UB.
+    // Precondition b) and c) combine to imply that if rhs is invariant in L,
+    // then a zero stride means the backedge can't be taken without executing
+    // undefined behavior.
     //
     // The positive stride case is the same as isKnownPositive(Stride) returning
     // true (original behavior of the function).
@@ -11657,7 +11659,7 @@
     //   A[i] = i;
     //
     if (PredicatedIV || !NoWrap || isKnownNonPositive(Stride) ||
-        !loopIsFiniteByAssumption(L))
+        !loopIsFiniteByAssumption(L) || !loopHasNoAbnormalExits(L))
       return getCouldNotCompute();
 
     if (!isKnownNonZero(Stride)) {


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