[llvm-bugs] [Bug 26668] New: Support cmpxchg of pointer type

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=26668

            Bug ID: 26668
           Summary: Support cmpxchg of pointer type
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Core LLVM classes
          Assignee: unassignedbugs at nondot.org
          Reporter: listmail at philipreames.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Today, we do not allow cmpxchg operations with pointer arguments.  We require
the frontend to insert ptrtoint casts and do the cmpxchg in integers.  While
correct, this is problematic from a couple of perspectives:
1) It makes the IR harder to analyse (for instance, it breaks capture tracking)
2) It pushes work onto the frontend authors for no real gain

The simplest implementation would be to introduce a lowering rule in
AtomicExpand that converts a cmpxchg of pointer type back to the inttoptr type
version the backends already understand.  Over time, we could migrate each
backend to natively selecting the pointer type.

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