[LLVMbugs] [Bug 7023] New: GVN slow on large function with lots of instructions

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=7023

           Summary: GVN slow on large function with lots of instructions
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: edwintorok at gmail.com
                CC: llvmbugs at cs.uiuc.edu


Created an attachment (id=4806)
 --> (http://llvm.org/bugs/attachment.cgi?id=4806)
l2.bc

LLVM 2.7 Release-Asserts build, GVN takes 0.7s on the attached bitcode (and
even more on some even larger bitcodes).

This is important in mesa's llvmpipe, where GVN takes up most of the
optimization time (and thus optimization time is higher than actual codegen
time)
;opt 650 ms (shader39)                       
;codegen 340 ms (shader39)
...
;opt 910 ms (shader76)
;codegen 430 ms (shader76)
;opt 930 ms (shader77)
;codegen 430 ms (shader77)

$ opt -gvn l2.bc -time-passes

  Total Execution Time: 0.7320 seconds (0.7351 wall clock)
   ---User Time---   --System Time--   --User+System--   ---Wall Time---  ---
Name ---
   0.7200 ( 99.4%)   0.0080 (100.0%)   0.7280 ( 99.5%)   0.7311 ( 99.5%) 
Global Value Numbering
   0.0040 (  0.6%)   0.0000 (  0.0%)   0.0040 (  0.5%)   0.0038 (  0.5%) 
Module Verifier
   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0001 (  0.0%) 
Memory Dependence Analysis
   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0001 (  0.0%) 
Dominator Tree Construction
   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%) 
Preliminary module verification
   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)  Basic
Alias Analysis (default AA impl)
   0.7240 (100.0%)   0.0080 (100.0%)   0.7320 (100.0%)   0.7351 (100.0%)  TOTAL

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