[LLVMbugs] [Bug 16398] New: functionattrs exhibits superlinear behaviour

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=16398

            Bug ID: 16398
           Summary: functionattrs exhibits superlinear behaviour
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Interprocedural Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: nlewycky at google.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

This is broken out from bug 13263. On the attached .ll file, we see this:

===-------------------------------------------------------------------------===
                      ... Pass execution timing report ...
===-------------------------------------------------------------------------===
  Total Execution Time: 4.9600 seconds (4.9723 wall clock)

   ---User Time---   --System Time--   --User+System--   ---Wall Time---  ---
Name ---
   3.8400 ( 78.0%)   0.0100 ( 25.0%)   3.8500 ( 77.6%)   3.8668 ( 77.8%) 
Deduce function attributes
   0.6800 ( 13.8%)   0.0000 (  0.0%)   0.6800 ( 13.7%)   0.6421 ( 12.9%)  SROA
   0.1800 (  3.7%)   0.0300 ( 75.0%)   0.2100 (  4.2%)   0.1741 (  3.5%) 
Function Integration/Inlining
   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0570 (  1.1%) 
Module Verifier
[...]

The slowdown is happening inside AddNoCaptureAttrs, and the capture tracking
analysis happens to be trivial so that isn't the problem (and SCCNodes.size()
== 1 so that also isn't the problem). I'm placing my bet on inefficient
AttributeSet manipulation.

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