[cfe-dev] Question on LiveVariables analysis

Guoping Long longguoping at gmail.com
Sun Oct 9 17:32:09 PDT 2011


Hi, Anna

   Here are steps on how I got this error:
1 Get the latest code:
    A. svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm
    B. svn co http://llvm.org/svn/llvm-project/cfe/trunk clang
2. Configure & Make
    A. make a separate directory for build: makedir llvm-build
    B. In llvm-build/, using cmake to generate the Makefile:
        cmake ../llvm -DCMAKE_BUILD_TYPE=Debug
    C. make & make install
3. Add a test:
    A. create a directory: tools/clang/examples/Debug
    B. write a test file, as attached.
    C. Modify tools/clang/CMakeLists.txt to build the examples/ directory.
    D. Add CMakeLists.txt in tools/clang/examples/Debug to build the newly
added test program.
    E. when the program is built, run it with the previous test program to
get this error.

I am using MacOS 10.6.8, x86-64 Intel platform.
It seems my source tree is not in the right configuration? Please let me
know what's wrong in my environment. I will be deeply appreciated. Thanks.

-------
Guoping

2011/10/9 Anna Zaks <ganna at apple.com>

> Hi Guoping,
>
> I cannot reproduce the assertion failure.
>
> Is it still reproducible with the latest revision of Clang/LLVM? If yes,
> can you send the command line you used.
>
> Thanks,
> Anna.
>
> On Oct 9, 2011, at 10:23 AM, Guoping Long wrote:
>
> Also, it seems there is an assert error in UninitializedValues.cpp. Giving
> this test program:
>   1 int main(int argc, char *argv[])
>   2 {
>   3   int x=3, y = 5, z = 6;
>   4
>   5   if(x<0) {
>   6     while(y>0){
>   7       y--;
>   8       x = z+1;
>   9     }
>  10   }else x = y;
>  11   return 0;
>  12 }
> Here is the assert error:
> Assertion failed: (res.getDeclRefExpr() == lastDR), function
> VisitUnaryOperator, file
> /Users/gplong/llvm/tools/clang/lib/Analysis/UninitializedValues.cpp, line
> 529.
> This message is triggered in call VisitUnaryOperator(). The line number may
> not be correct because I added some print statements.
>
> -----
> Guoping
>
> 2011/10/8 Guoping Long <longguoping at gmail.com>
>
>> On my testing environment, the UninitializedValues.cpp has the same
>> problem (do not have any output). Both analyses are based on the StmtVisitor
>> interface.  I think there may be a version mismatch, that is these two
>> analyses are based on an older version of StmtVisitor class to work?  I just
>> downloaded a new version from website and did all tests again and still have
>> this problem.
>>
>> ----
>> Guoping
>>
>>
>> 2011/10/8 Guoping Long <longguoping at gmail.com>
>>
>>> Hi, Ted
>>>
>>>    I will be very curious why results in your environment are correct.
>>> Attached is my test code. I stepped into the program using GDB, it turned
>>> out that no live variables can be found. Take the last return statement in
>>> my previous example program as an example: return b * d + c. The transfer
>>> function eventually called the default StmtVisit function which did not
>>> recognize variables b, d, c which are actually used.The only function in
>>> LiveVariables.cpp that can generate live variables is VisitDeclRefExpr(),
>>> but when running the program this function is never called.
>>>
>>>   I am using the newest version of Clang/LLVM. Is it because my
>>> environment setup is wrong?
>>>
>>> ----
>>> Guoping
>>>
>>> 2011/10/7 Ted Kremenek <kremenek at apple.com>
>>>
>>>> This is what I am seeing:
>>>>
>>>> $ clang -cc1 -analyze -analyzer-checker=debug.DumpLiveVars t.c
>>>>
>>>> [ B0 (live variables at block exit) ]
>>>>
>>>> [ B1 (live variables at block exit) ]
>>>>
>>>> [ B2 (live variables at block exit) ]
>>>>  b <t.c:2:10>
>>>>  d <t.c:2:16>
>>>>
>>>> [ B3 (live variables at block exit) ]
>>>>  a <t.c:2:7>
>>>>  b <t.c:2:10>
>>>>  d <t.c:2:16>
>>>>
>>>> [ B4 (live variables at block exit) ]
>>>>
>>>>
>>>> I also think the number of the blocks is not quite right in your
>>>> example, or at least how they correspond to Clang's CFG:
>>>>
>>>> $ clang -cc1 -analyze -analyzer-checker=debug.DumpCFG t.c
>>>>
>>>>  [ B4 (ENTRY) ]
>>>>     Predecessors (0):
>>>>     Successors (1): B3
>>>>
>>>>  [ B1 ]
>>>>       1: 4
>>>>       2: c
>>>>       3: [B1.2] = [B1.1]
>>>>       4: b
>>>>       5: [B1.4]
>>>>       6: d
>>>>       7: [B1.6]
>>>>       8: [B1.5] * [B1.7]
>>>>       9: c
>>>>      10: [B1.9]
>>>>      11: [B1.8] + [B1.10]
>>>>      12: return [B1.11];
>>>>     Predecessors (2): B2 B3
>>>>     Successors (1): B0
>>>>
>>>>  [ B2 ]
>>>>       1: a
>>>>       2: [B2.1]
>>>>       3: b
>>>>       4: [B2.3]
>>>>       5: [B2.2] + [B2.4]
>>>>       6: c
>>>>       7: [B2.6] = [B2.5]
>>>>       8: 2
>>>>       9: d
>>>>      10: [B2.9] = [B2.8]
>>>>     Predecessors (1): B3
>>>>     Successors (1): B1
>>>>
>>>>  [ B3 ]
>>>>       1: int a;
>>>>       2: int b;
>>>>       3: int c;
>>>>       4: int d;
>>>>       5: int x;
>>>>       6: 3
>>>>       7: a
>>>>       8: [B3.7] = [B3.6]
>>>>        9: 5
>>>>      10: b
>>>>      11: [B3.10] = [B3.9]
>>>>      12: 4
>>>>      13: d
>>>>      14: [B3.13] = [B3.12]
>>>>      15: 100
>>>>      16: x
>>>>      17: [B3.16] = [B3.15]
>>>>      18: a
>>>>      19: [B3.18]
>>>>      20: b
>>>>      21: [B3.20]
>>>>      22: [B3.19] > [B3.21]
>>>>       T: if [B3.22]
>>>>     Predecessors (1): B4
>>>>     Successors (2): B2 B1
>>>>
>>>>  [ B0 (EXIT) ]
>>>>     Predecessors (1): B1
>>>>     Successors (0):
>>>>
>>>>
>>>> Block B3 is actually the entrance block, since the CFG is built
>>>> bottom-up.
>>>>
>>>> Perhaps there is something not quite right with how you are running the
>>>> checkers?
>>>>
>>>> On Oct 7, 2011, at 9:32 PM, Guoping Long wrote:
>>>>
>>>> Hi,
>>>>
>>>>    While LiveVariables analysis
>>>> (tools/clang/lib/Analysis/LiveVariables.cpp) does not generate any output?
>>>> Specifically, for this simple program:
>>>>   1 int main(int argc, char *argv[])
>>>>   2 {
>>>>   3   int a,b,c,d,x;
>>>>   4
>>>>   5   a = 3;   //Basic block B1
>>>>   6   b = 5;
>>>>   7   d = 4;
>>>>   8   x = 100;
>>>>   9
>>>>  10   if(a>b){  //Basic block B2
>>>>  11     c = a+b;
>>>>  12     d = 2;
>>>>  13   }
>>>>  14
>>>>  15   c = 4;   //Basic block B3
>>>>  16   return b * d + c;
>>>>  17 }
>>>> This simple example is taken from this wiki page illustrating live
>>>> variables analysis (http://en.wikipedia.org/wiki/Live_variable_analysis
>>>> ).
>>>> Both B2 and B3 should have live variables, but the output (using
>>>> LiveVariables::dumpBlockLiveness(SourceManager &)) says no live variables
>>>> exist. I am trying to use this analysis as an example on how to write a good
>>>> analysis algorithm for Clang, but really did not expect this behavior for
>>>> this analysis.
>>>> Anybody who knows the answer please let me know. Many thanks!!!
>>>>
>>>> --------
>>>> Guoping
>>>> _______________________________________________
>>>> cfe-dev mailing list
>>>> cfe-dev at cs.uiuc.edu
>>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>>>>
>>>>
>>>>
>>>
>>
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