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Fix #15155 FN accessMoved (string concatenation using +=) #8996

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Fix #15155 FN accessMoved (string concatenation using +=) #8996

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dada503
Update vf_analyzers.cpp
chrchr-github Nov 5, 2026
30484de
Update testnullpointer.cpp
chrchr-github Nov 5, 2026
5812614
Update testvalueflow.cpp
chrchr-github Nov 5, 2026
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3 changes: 2 additions & 1 deletion lib/vf_analyzers.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -228,7 +228,8 @@ struct ValueFlowAnalyzer : Analyzer {
if (inconclusive)
return Action::Read | Action::Inconclusive;
if (isVariableChanged(tok, getIndirect(tok), getSettings())) {
if (Token::Match(tok->astParent(), "*|[|.|++|--"))
if (Token::Match(tok->astParent(), "*|[|.|++|--") ||
(tok->astParent() && tok->astParent()->isAssignmentOp() && tok->astParent()->str().size() == 2)) // compound assignment

@dmcppcheck dmcppcheck Nov 6, 2026

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AI review

str().size() == 2 misses <<= and >>= (both 3 characters). For a moved S x with S& operator<<=(int), x <<= 1; still gets no accessMoved, while x += 1; now does. With uninitialized ints, x += y now gives uninitvar but x <<= y stays legacyUninitvar. tok->astParent()->str() != "=" would cover all compound assignments.

return Action::Read | Action::Invalid;
// Check if its assigned to the same value
if (value && !value->isImpossible() && Token::simpleMatch(tok->astParent(), "=") && astIsLHS(tok) &&
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2 changes: 1 addition & 1 deletion test/testnullpointer.cpp
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Expand Up @@ -4707,7 +4707,7 @@ class TestNullPointer : public TestFixture {
" p += a;\n"
" *p = 0;\n"
"}\n");
ASSERT_EQUALS("", errout_str());
ASSERT_EQUALS("[test.cpp:2:7]: (error) Pointer addition with NULL pointer. [nullPointerArithmetic]\n", errout_str());

check("int f(int *p = 0) {\n"
" if (p == 0) {\n"
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6 changes: 6 additions & 0 deletions test/testvalueflow.cpp
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Expand Up @@ -1110,6 +1110,12 @@ class TestValueFlow : public TestFixture {
" g(std::move(x)).f(1);\n"
"}\n";
ASSERT_EQUALS(false, testValueOfX(code, 5U, ValueFlow::Value::MoveKind::MovedVariable));

code = "void f(std::string x) {\n" // #15155
" std::string a{ std::move(x) };\n"
" x += \"abc\";\n"
"}\n";
ASSERT_EQUALS(true, testValueOfX(code, 3U, ValueFlow::Value::MoveKind::MovedVariable));
}

void valueFlowCalculations() {
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