Fix LSE-array overlap issue
In cases where an array has overlapping accesses on separate
iterations LSE could get confused and incorrectly believe removing
array stores is safe even when later iterations rely on the store
occurring. For example consider the following code:
```
int do_cal(int len) {
if (len < 5) {
return -1;
}
int w[] = new w[len];
int t = 0;
for (int i = 5; i < w.length; i++) {
w[i] = please_interleave(w[i - 1], w[i - 5]);
t = please_select(w[i], i);
}
return t;
}
```
We would either need to materialize 5 PHIs to hold the values
`w[i - 1], ..., w[i - 5]` or avoid removing the write to `w[i]`. Our
LSE pass is unable to do the former and would (incorrectly) fail to
recognize that, by not being able to determine the values of `w[i -
1]` and `w[i-5]` that the later store to `w[i]` must be preserved.
Bug: 168446366
Test: ./test.py --host
Change-Id: I89772c8bf49ebf6de70f86bd68484e14bd189406
4 files changed