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Fix #15145 FN knownArgumentHiddenVariableExpression in if scope #8974

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Fix #15145 FN knownArgumentHiddenVariableExpression in if scope #8974

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a2c9ccf
Update checkother.cpp
chrchr-github Oct 28, 2026
246b6e6
Update testother.cpp
chrchr-github Oct 28, 2026
e04ce1d
Update checkother.cpp
chrchr-github Oct 28, 2026
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3 changes: 2 additions & 1 deletion lib/checkother.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4405,7 +4405,8 @@ void CheckOtherImpl::checkKnownArgument()
if (Token::Match(child, "%var%|.|[")) {
if (child->hasKnownIntValue())
return ChildrenToVisit::none;
if (astIsIntegral(child, false) && !astIsPointer(child) && child->values().empty()) {
if (astIsIntegral(child, false) && !astIsPointer(child) &&
(child->values().empty() || (child->values().front().isIntValue() && child->values().front().isImpossible()))) {

@dmcppcheck dmcppcheck Oct 29, 2026

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AI review

Accepting a variable whose first value is impossible also lets through comparisons whose result follows from those impossible values, and those warnings are wrong. With this PR:

  • void f(int x) { if (x != 0) g(x == 0); } gives Argument 'x==0' to function g is always 0. It does not matter what value 'x' has. [knownArgument]
  • if (x < 0) return; g(x >= 0); gives the same kind of warning.
  • void f(unsigned x) { g(x >= 0); } and g(x < 0) give the same kind of warning, on top of the existing unsignedPositive / unsignedLessThanZero.

The value of x is what decides each of these results, so "It does not matter what value 'x' has" is misleading. Base reports none of them. Consider accepting impossible values only when a constant literal (0*x, x&0, ...) hides the variable, or skipping comparison operators here, and add a negative test such as if (x != 0) g(x == 0);.

vartok = child;
return ChildrenToVisit::done;
}
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7 changes: 7 additions & 0 deletions test/testother.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13822,6 +13822,13 @@ class TestOther : public TestFixture {
"[test.cpp:5:18]: (style) Argument 'true||x' to function dostuff is always 1. Constant literal calculation disable/hide variable expression 'x'. [knownArgumentHiddenVariableExpression]\n"
"[test.cpp:6:15]: (style) Argument 'x*0' to function dostuff is always 0. Constant literal calculation disable/hide variable expression 'x'. [knownArgumentHiddenVariableExpression]\n"
"[test.cpp:7:15]: (style) Argument '0*x' to function dostuff is always 0. Constant literal calculation disable/hide variable expression 'x'. [knownArgumentHiddenVariableExpression]\n", errout_str());

check("void f(int x) {\n" // #15145
" if (x != 0)\n"
" g(0 * x);\n"
"}\n");
ASSERT_EQUALS("[test.cpp:3:13]: (style) Argument '0*x' to function g is always 0. Constant literal calculation disable/hide variable expression 'x'. [knownArgumentHiddenVariableExpression]\n",
errout_str());
}

void knownArgumentTernaryOperator() { // #10374
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