[SCCP] Pointer equality propagated without regard to provenance

[nikic]

https://llvm.godbolt.org/z/jPns55Tjn

; RUN: opt -S -passes=sccp < %s
define ptr @src(ptr %x) {
  %cmp = icmp eq ptr %x, inttoptr (i64 12345678 to ptr)
  call void @llvm.assume(i1 %cmp)
  ret ptr %x
}

define ptr @tgt(ptr %x) {
  %cmp = icmp eq ptr %x, inttoptr (i64 12345678 to ptr)
  call void @llvm.assume(i1 %cmp)
  ret ptr inttoptr (i64 12345678 to ptr)
}

This does not take into account that the two pointers may have different provenance. We've fixed this in other places like GVN, but not in SCCP apparently.

[antoniofrighetto]

Patch is ready, there are a bunch of test failures though, taking a look...

[nikic]

A thing to note here is that we only want to prevent this specifically for equalities established via PredicateInfo, not for straightforward propagation. Ideally we'd also respect the logic that allows replacement at specific uses where provenance does not matter, but I'm not sure how to do this best.