[LLVMbugs] [Bug 11718] New: ExeDepsFix seems to use exponential amount of memory on large functions

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=11718

             Bug #: 11718
           Summary: ExeDepsFix seems to use exponential amount of memory
                    on large functions
           Product: libraries
           Version: 3.0
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: ddneff at hotmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


With large functions, the ExeDepsFix pass seems to use exponential amounts of
memory.  A 100K instruction function with ~2k basic blocks took over 96GB of
memory (not sure exactly how much is required to complete, my machine only has
96GB).  I think this may be related to using a SmallVector<MachineInstr*, 8>
for DomainValue::Instrs and then inserting duplicate instructions into this
vector. Swapping out this SmallVector for a SmallPtrSet seems to fix the
problem; I don't know if that is a great solution, but memory useage for this
use case drops from 96GB to practically nothing (assuming I didn't break the
algorithm somehow).

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