[llvm] [LV] Follow up to uncountable exit with side effects vectorization (PR #201589)

[Graham Hunter via llvm-commits]

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@@ -4210,6 +4210,31 @@ struct EarlyExitInfo {
 
 /// Update \p Plan to mask memory operations in the loop based on whether the
 /// early exit is taken or not.
+//
+// We're currently expecting to find a loop with properties similar to the
+// following C code:
+//
+//   #define N 10000
+//   int cond[N];
+//   int src[N];
+//   int dst[N];
+//
+//   void foo(int threshold) {
+//     for (int i=0; i<N; ++i) {
+//       if (cond[i] > threshold)
+//         break;
+//       dst[i] = src[i] + 42;
+//     }
+//   }
+//
+// The loop must have a single unconditional load contributing to the
+// uncountable exit comparison, and the other term must be loop-invariant.
+// There must also be a counted exit. Other memory operations in the loop can
+// take place before or after the uncountable exit, but must also be
+// unconditional. All potential accesses to the memory used for the load for the
+// exit condition must be guaranteed to be dereferenceable. Any stores within
+// the loop must not alias with any other memory operations.
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huntergr-arm wrote:

done.

https://github.com/llvm/llvm-project/pull/201589