[cfe-dev] Question on LiveVariables analysis

[Guoping Long]

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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