LoopReroll incorrectly reorders memory instrs when there is overlap

[llvmbot]

Bugzilla Link	47658
Version	trunk
OS	All
Reporter	LLVM Bugzilla Contributor
CC	@efriedma-quic,@hfinkel,@jmolloy,@zhengyang92,@nunoplopes,@regehr

Extended Description

Test: Transforms/LoopReroll/basic.ll
Function: pointer_bitcast_baseinst
Reason: Memory mismatch

Example: https://godbolt.org/z/5c8YK1
Ordering of loads and stores with memory offsets:

source - load 876, load 892, store 892, store 900, ...
target - load 876, store 892, load 892, store 900, ...

Since there is overlap between the memory positions of the second load and first store in source then the swapped ordering of these instructions in target is incorrect.
This optimization should not be performed in case of such a memory overlap.

A detailed and complete Alive report with single iteration loop unroll on this test can be seen here: https://pastebin.com/pQsf61wb

[nunoplopes]

Here's a manually unrolled report from Alive2: https://alive2.llvm.org/ce/z/tmuXZ_

[nikic]

The LoopReroll pass has been removed by #80972.