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cppcheck
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Fix some false positives when the same expression at different places does not have the same value 

Typically with
```
int F(int *f);
void F2(int *a, int *b) {
  int c = *a;
  F(a); // modifies *a
  if (b && c != *a) {}
}
```
we would get the following FP:
```
[test.cpp:3] -> [test.cpp:5]: (style) The comparison 'c != *a' is always false because 'c' and '*a' represent the same value.\n
```

I guess it boils down to isSameExpression only checking that the
expression is the same (in the above case, "*a" and "*a" are indeed the
same), but there's not real check on the values.
So the patch here is a bit hackish, and we still have false negatives in
cases with dereferenced pointers.
This commit is contained in:
Ken-Patrick Lehrmann 2020-07-11 13:42:57 +02:00
parent 27841d6b81
commit 61ccf888b3
2 changed files with 32 additions and 1 deletions
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4
lib/checkother.cpp
View File

@ -2014,7 +2014,9 @@ void CheckOther::checkDuplicateExpression()
if (tok->isOp() && tok->astOperand1() && !Token::Match(tok, "+|*|<<|>>|+=|*=|<<=|>>=")) {
if (Token::Match(tok, "==|!=|-") && astIsFloat(tok->astOperand1(), true))
continue;
const bool followVar = !isConstVarExpression(tok) || Token::Match(tok, "%comp%|%oror%|&&");
const bool pointerDereference = (tok->astOperand1() && tok->astOperand1()->isUnaryOp("*")) ||
(tok->astOperand2() && tok->astOperand2()->isUnaryOp("*"));
const bool followVar = (!isConstVarExpression(tok) || Token::Match(tok, "%comp%|%oror%|&&")) && !pointerDereference;
if (isSameExpression(mTokenizer->isCPP(),
true,
tok->astOperand1(),

29
test/testother.cpp
View File

@ -243,6 +243,8 @@ private:
TEST_CASE(unusedVariableValueTemplate); // #8994
TEST_CASE(moduloOfOne);
TEST_CASE(sameExpressionPointers);
}
void check(const char code[], const char *filename = nullptr, bool experimental = false, bool inconclusive = true, bool runSimpleChecks=true, bool verbose=false, Settings* settings = nullptr) {
@ -5484,6 +5486,24 @@ private:
ASSERT_EQUALS("[test.cpp:2] -> [test.cpp:3]: (style) The comparison 'val < 0' is always false.\n"
"[test.cpp:2] -> [test.cpp:4]: (style) The comparison 'val > 0' is always false.\n", errout.str());
check("void f() {\n"
" int val = 0;\n"
" int *p = &val;n"
" val = 1;\n"
" if (*p < 0) continue;\n"
" if ((*p > 0)) {}\n"
"}\n");
ASSERT_EQUALS("", errout.str());
check("void f() {\n"
" int val = 0;\n"
" int *p = &val;n"
" if (*p < 0) continue;\n"
" if ((*p > 0)) {}\n"
"}\n");
TODO_ASSERT_EQUALS("[test.cpp:2] -> [test.cpp:3]: (style) The comparison '*p < 0' is always false.\n"
"[test.cpp:2] -> [test.cpp:4]: (style) The comparison '*p > 0' is always false.\n", "", errout.str());
check("void f() {\n"
" int val = 0;\n"
" if (val < 0) {\n"
@ -8701,6 +8721,15 @@ private:
ASSERT_EQUALS("", errout.str());
}
void sameExpressionPointers() {
check("int f(int *i);\n"
"void g(int *a, int *b) {\n"
" int c = *a;\n"
" f(a);\n"
" if (b && c != *a) {}\n"
"}\n");
ASSERT_EQUALS("", errout.str());
}
};
REGISTER_TEST(TestOther)