[llvm] [LV] Ignore user-specified interleave count when unsafe. (PR #153009)

[David Sherwood via llvm-commits]

================
@@ -9842,7 +9842,7 @@ bool LoopVectorizePass::processLoop(Loop *L) {
 
   // Get user vectorization factor and interleave count.
   ElementCount UserVF = Hints.getWidth();
-  unsigned UserIC = Hints.getInterleave();
+  unsigned UserIC = LVL.isSafeForAnyVectorWidth() ? Hints.getInterleave() : 1;
----------------
david-arm wrote:

If the user didn't specify an interleave hint then `Hints.getInterleave()` actually returns 0. If `LVL.isSafeForAnyVectorWidth` returns false and there is no hint you'd be setting UserIC to 1 instead of 0. I wonder if it's better to rewrite this as:

```
  unsigned UserIC = Hints.getInterleave();
  if (UserIC > 1 && !LVL.isSafeForAnyVectorWidth())
    UserIC = 1;
```

https://github.com/llvm/llvm-project/pull/153009