[llvm] [SLP]Support LShr as base for copyable elements (PR #153393)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

hi, this introduces crashes, even at head after the fixes:

```
$ cat /tmp/a.ll
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

define void @_RNvMs0_NtCsjIjFnkOzZDy_6object5writeNtB5_6Object4emit() {
.loopexit381:
  %0 = trunc i64 0 to i32
  %1 = select i1 false, i32 %0, i32 0
  %2 = trunc i64 0 to i32
  %3 = select i1 false, i32 %2, i32 0
  %4 = add i32 %2, 0
  %5 = select i1 false, i32 %4, i32 0
  br label %6

6:                                                ; preds = %.loopexit381
  %7 = getelementptr i8, ptr null, i64 12
  store i32 %1, ptr %7, align 4
  %8 = getelementptr i8, ptr null, i64 16
  store i32 %1, ptr %8, align 4
  %9 = getelementptr i8, ptr null, i64 20
  store i32 %3, ptr %9, align 4
  %10 = getelementptr i8, ptr null, i64 24
  store i32 %5, ptr %10, align 4
  ret void
}
$ build/rel/bin/opt -p slp-vectorizer -disable-output /tmp/a.ll
opt: ../../llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:5048: int llvm::slpvectorizer::BoUpSLP::ScheduleCopyableData::incrementUnscheduledDeps(int): Assertion `UnscheduledDeps >= 0 && "invariant"' failed.
```

https://github.com/llvm/llvm-project/pull/153393