[llvm-bugs] [Bug 31764] New: DenseMapInfo for PointerEmbeddedInt runs afoul of assertions

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=31764

            Bug ID: 31764
           Summary: DenseMapInfo for PointerEmbeddedInt runs afoul of
                    assertions
           Product: libraries
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Support Libraries
          Assignee: unassignedbugs at nondot.org
          Reporter: jordan_rose at apple.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

The DenseMapInfo for PointerEmbeddedInt looks like this:

  static inline T getEmptyKey() { return IntInfo::getEmptyKey(); }
  static inline T getTombstoneKey() { return IntInfo::getTombstoneKey(); }

But the empty and tombstone values for a pointer-sized integer are likely out
of range for a PointerEmbeddedInt, which means we immediately get assertion
failures when DenseMap tries to use these values. At the very least we should
be truncating the right number of bits; a more holistic solution would allow
DenseMap to store a different representation than the formal key type.

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