[llvm-bugs] [Bug 33126] New: MemorySSA could cache alias query results more aggressively

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=33126

            Bug ID: 33126
           Summary: MemorySSA could cache alias query results more
                    aggressively
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: davide at freebsd.org
                CC: dberlin at dberlin.org, george.burgess.iv at gmail.com,
                    llvm-bugs at lists.llvm.org

Dumping this one here, for whomever gets to it first (as I have a terrible
memory, and probably will forget in a day or two).

Dan run ./opt -memoryssa on clang.bc and statistics return:

1175012 memoryssa       - Number of MemorySSA alias queries
360784 memoryssa       - Number of MemorySSA duplicate pointer queries

Which is a pretty significant amount of duplicate queries.
In the conducted experiments, caching everything saves 20% of MemorySSA time,
but the amount of memory used could be a concern for large testcases (e.g.
LTO).

Probably using a smarter cache could lead to substantial benefits without
memory usage going crazy. It's unclear what's the best policy, maybe LRU is a
good starting point.

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