[cfe-dev] Question on LiveVariables analysis

[Guoping Long]

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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