[llvm-bugs] [Bug 35338] New: Clients of SelectionDAG::ReplaceAllUsesWith drop debug info, & are inconsistent

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=35338

            Bug ID: 35338
           Summary: Clients of SelectionDAG::ReplaceAllUsesWith drop debug
                    info, & are inconsistent
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: vsk at apple.com
                CC: llvm-bugs at lists.llvm.org

There are a few issues here:

- CombineTo() calls ReplaceAllUsesWith(), which calls transferDbgValues(). If
we assert that debug line/value information is preserved after the RAUW in
CombineTo(), a bunch of tests fail.

- Clients of transferDbgValues() pass it SDValues which are attached to SDNodes
with invalidated debug info. It seems unfortunate that we'd even try to
propagate invalid debug info.

- One overload of ReplaceAllUsesWith(From, To) requires From != To, but another
doesn't. This is partly annoying, but may also be masking correctness issues.

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