[PATCH] D19984: [LV] Preserve order of dependences in interleaved accesses analysis

[Adam Nemet via llvm-commits]

anemet added inline comments.

================
Comment at: lib/Transforms/Vectorize/LoopVectorize.cpp:5254-5258
@@ -5162,1 +5253,7 @@
 
+      // If A and B cannot be reordered, we can't add additional instructions
+      // to A's group since this may cause illegal code motion. If B is already
+      // in a group release it.
+      if (!canReorderMemAccesses(&*II, &*I)) {
+        if (isInterleaved(B)) {
+          InterleaveGroup *StoreGroup = getInterleaveGroup(B);
----------------
Matt, I am not sure I follow, which of these accesses is not constant distance in my example?

I just tried this example:


```
void
f(char *a, char * __restrict c, int n) {
  for (int i = 0; i < n; i+=3) {
    c[i] = a[i];
    a[i+4] = c[i+4];
    c[i+1] = a[i+1];
  }
}

```
If you compile this on x86_64 with:

```
-O3 -mllvm -enable-load-pre=0 -mllvm -store-to-load-forwarding-conflict-detection=0 -mllvm -enable-interleaved-mem-accesses -mllvm -force-vector-width=2
```

Then the loads from 'a' will be merged which breaks the forward dependence between  the store of a[i+4] and the load of a[i+1].

No?


http://reviews.llvm.org/D19984