[llvm-bugs] [Bug 24598] New: BasicAliasAnalysis/getModRefInfo excessive compile time for this short example

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=24598

            Bug ID: 24598
           Summary: BasicAliasAnalysis/getModRefInfo excessive compile
                    time for this short example
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: yaron.keren at gmail.com
                CC: chandlerc at gmail.com, echristo at gmail.com,
                    igor at azulsystems.com, llvm-bugs at lists.llvm.org,
                    tzafrir11 at gmail.com
    Classification: Unclassified

sh-4.3$ cat < AliasSet.cpp

void foo(char *, char *);
void bar(int Size, bool flag) {
  for (int i = 0; i < Size; ++i) {
    char text[1];
    char buff[1];
    if (flag)
      foo(text, buff);
  }
}

sh-4.3$ ./runme.sh
++ clang++ -O2 -march=x86-64 -c AliasSet.cpp

real    0m0.072s
user    0m0.000s
sys     0m0.016s
++ clang++ -O3 -march=x86-64 -c AliasSet.cpp

real    0m1.135s
user    0m0.000s
sys     0m0.015s
++ clang++ -O2 -march=sandybridge -c AliasSet.cpp

real    0m0.068s
user    0m0.000s
sys     0m0.015s
++ clang++ -O3 -march=sandybridge -c AliasSet.cpp

real    0m17.028s
user    0m0.015s
sys     0m0.000s

As of current SVN, r246146. Profiling shows all time is spent around alias
analysis, slow at O3 and very slow at O3 for sandybridge architecture.
Reproduced on Linux and Windows.

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