[PATCH] new check checking use of identical expressions inside a conditional expression, i.e. '?'.

[Per Viberg]

Hi,

This patch adds a check that warns for usage of identical expressions inside a conditional expression, i.e. '?'.
example:

unsigned a = 1;
unsigned b = 2;
unsigned c = a > 5 ? a+b : a+b;

generates warning
"identical expressions on both sides of ':' in conditional expression"
see test file identical-expression.cpp for more details.


Benchmarking results:

LLVM/Clang build time: 
time without check: 17415.63 seconds (scan-build --use-analyzer clang -enable-checker)
time without check: 17508.07 seconds (scan-build --use-analyzer clang -enable-checker alpha.core.IdenticalExpr)
increase:  92,44 seconds 
increase in percent:  0.53 %  (IdenticalExpr includes check for of use of identical expressions with comparison operators as well).

Validation results:

Run check on selected open source C/C++ projects:
LLVM/Clang --> no positives, false or true.
cppchecker --> no positives, false or true.
redis --> no positives, false or true.
rethinkdb --> no positives, false or true.

Verification results:

Tested against identical-expressions.cpp: no failed tests. 
(see test file: identical-expression.cpp) 


Best regards,
Per

.......................................................................................................................
Per Viberg Senior Engineer
Evidente ES East AB  Warfvinges väg 34  SE-112 51 Stockholm  Sweden
Phone:    +46 (0)8 402 79 00
Mobile:    +46 (0)70 912 42 52
E-mail:     Per.Viberg at evidente.se

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