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Fix #14660 Handle reverse conditions in isOppositeCond function #8408

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Merged
danmar merged 3 commits into from
Apr 12, 2026
+52 −12
Merged

Fix #14660 Handle reverse conditions in isOppositeCond function #8408

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4fc115d
Handle reverse conditions in isOppositeCond function
francois-berder Apr 1, 2026
37efa2e
fixup! Handle reverse conditions in isOppositeCond function
francois-berder Apr 5, 2026
303be34
fixup! fixup! Handle reverse conditions in isOppositeCond function
francois-berder Apr 10, 2026
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58 changes: 46 additions & 12 deletions lib/astutils.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1810,21 +1810,31 @@ bool isSameExpression(bool macro, const Token *tok1, const Token *tok2, const Se
return commutativeEquals;
}

static bool isZeroBoundCond(const Token * const cond)
static bool isZeroBoundCond(const Token * const cond, bool reverse)
{
if (cond == nullptr)
if (cond == nullptr || !cond->isBinaryOp())
return false;

const Token* op = reverse ? cond->astOperand1() : cond->astOperand2();
if (!op->hasKnownIntValue())
return false;

// Assume unsigned
// TODO: Handle reverse conditions
const bool isZero = cond->astOperand2()->getValue(0);
if (cond->str() == "==" || cond->str() == ">=")
const bool isZero = op->getKnownIntValue() == 0;
std::string cmp = cond->str();
if (reverse) {
if (cmp[0] == '>')
cmp[0] = '<';
else if (cmp[0] == '<')
cmp[0] = '>';
}

if (cmp == "==" || cmp == ">=")
return isZero;
if (cond->str() == "<=")
if (cmp == "<=")
return true;
if (cond->str() == "<")
if (cmp == "<")
return !isZero;
if (cond->str() == ">")
return false;
return false;
}

Expand Down Expand Up @@ -1888,7 +1898,7 @@ bool isOppositeCond(bool isNot, const Token * const cond1, const Token * const c
if (isSameExpression(true, cond1->astOperand2(), cond2->astOperand2(), settings, pure, followVar, errors))
return isDifferentKnownValues(cond1->astOperand1(), cond2->astOperand1());
}
// TODO: Handle reverse conditions

if (Library::isContainerYield(cond1, Library::Container::Yield::EMPTY, "empty") &&
Library::isContainerYield(cond2->astOperand1(), Library::Container::Yield::SIZE, "size") &&
isSameExpression(true,
Expand All @@ -1898,7 +1908,19 @@ bool isOppositeCond(bool isNot, const Token * const cond1, const Token * const c
pure,
followVar,
errors)) {
return !isZeroBoundCond(cond2);
return !isZeroBoundCond(cond2, false);
}

if (Library::isContainerYield(cond1, Library::Container::Yield::EMPTY, "empty") &&
Library::isContainerYield(cond2->astOperand2(), Library::Container::Yield::SIZE, "size") &&
isSameExpression(true,
cond1->astOperand1()->astOperand1(),
cond2->astOperand2()->astOperand1()->astOperand1(),
settings,
pure,
followVar,
errors)) {
return !isZeroBoundCond(cond2, true);
}

if (Library::isContainerYield(cond2, Library::Container::Yield::EMPTY, "empty") &&
Expand All @@ -1910,7 +1932,19 @@ bool isOppositeCond(bool isNot, const Token * const cond1, const Token * const c
pure,
followVar,
errors)) {
return !isZeroBoundCond(cond1);
return !isZeroBoundCond(cond1, false);
}

if (Library::isContainerYield(cond2, Library::Container::Yield::EMPTY, "empty") &&
Library::isContainerYield(cond1->astOperand2(), Library::Container::Yield::SIZE, "size") &&
isSameExpression(true,
cond2->astOperand1()->astOperand1(),
cond1->astOperand2()->astOperand1()->astOperand1(),
settings,
pure,
followVar,
errors)) {
return !isZeroBoundCond(cond1, true);
}
}

Expand Down
6 changes: 6 additions & 0 deletions test/testcondition.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2674,6 +2674,12 @@ class TestCondition : public TestFixture {
check("void f1(const std::string &s) { if(s.size() >= 0) if(s.empty()) {}} "); // CheckOther says: Unsigned expression 's.size()' can't be negative so it is unnecessary to test it. [unsignedPositive]
ASSERT_EQUALS("", errout_str());

check("void f1(const std::string &s) { if(42 < s.size()) if(s.empty()) {}}");
ASSERT_EQUALS("[test.cpp:1:39] -> [test.cpp:1:61]: (warning) Opposite inner 'if' condition leads to a dead code block. [oppositeInnerCondition]\n", errout_str());
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@danmar danmar Apr 12, 2026

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hmm I feel it's out of scope for this PR but I feel the warning message is a bit obfuscated. The "leads to a dead code block" is true but it's an indirect consequence. I think it would be better to try to describe the direct consequence that inner condition s.empty() is always false.
I also feel that sometimes opposite inner conditions doesn't necessarily lead to dead code.. i.e.: if (x < 0 || s.empty()) I don't know if we warn but imho it should be OK to warn if the message is clear..


check("void f1(const std::string &s) { if(s.empty()) if(42 < s.size()) {}}");
ASSERT_EQUALS("[test.cpp:1:43] -> [test.cpp:1:53]: (warning) Opposite inner 'if' condition leads to a dead code block. [oppositeInnerCondition]\n", errout_str());

// TODO: These are identical condition since size cannot be negative
check("void f1(const std::string &s) { if(s.size() <= 0) if(s.empty()) {}}");
ASSERT_EQUALS("", errout_str());
Expand Down
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