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Integer overflow; generalized checking for nonportable code

This commit is contained in:
Daniel Marjamäki 2021-01-04 19:43:05 +01:00
parent 01c434f8bf
commit abd6c00c82
1 changed files with 50 additions and 28 deletions
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78
lib/checktype.cpp
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@ -20,6 +20,7 @@
//---------------------------------------------------------------------------
#include "checktype.h"
#include "astutils.h"
#include "mathlib.h"
#include "platform.h"
#include "settings.h"
@ -229,6 +230,7 @@ void CheckType::integerOverflowError(const Token *tok, const ValueFlow::Value &v
void CheckType::checkIntegerOverflowOptimisations()
{
// Interesting blogs:
// https://www.airs.com/blog/archives/120
// https://kristerw.blogspot.com/2016/02/how-undefined-signed-overflow-enables.html
// https://research.checkpoint.com/2020/optout-compiler-undefined-behavior-optimizations/
@ -247,38 +249,58 @@ void CheckType::checkIntegerOverflowOptimisations()
if (!Token::Match(tok, "<|<=|>=|>") || !tok->isBinaryOp())
continue;
const std::string &cmp = tok->str();
const Token * const lhs = tok->astOperand1();
if (!Token::Match(lhs, "[+-]") || !lhs->isBinaryOp() || !lhs->valueType() || !lhs->valueType()->isIntegral() || lhs->valueType()->sign != ValueType::Sign::SIGNED)
continue;
const Token *lhsTokens[2] = {tok->astOperand1(), tok->astOperand2()};
for (const Token *lhs: lhsTokens) {
std::string cmp = tok->str();
if (lhs == tok->astOperand2())
cmp[0] = (cmp[0] == '<') ? '>' : '<';
const Token *expr = lhs->astOperand1();
const Token *other = lhs->astOperand2();
if (expr->varId() == 0 || expr->varId() != lhs->astSibling()->varId())
continue;
if (!Token::Match(lhs, "[+-]") || !lhs->isBinaryOp() || !lhs->valueType() || !lhs->valueType()->isIntegral() || lhs->valueType()->sign != ValueType::Sign::SIGNED)
continue;
// x [+-] c cmp x
if (other->isNumber() && other->getKnownIntValue() > 0) {
bool result;
if (tok->astOperand1()->str() == "+")
result = (cmp == ">" || cmp == ">=");
else
result = (cmp == "<" || cmp == "<=");
integerOverflowOptimisationError(tok, result ? "true" : "false");
}
const Token *exprTokens[2] = {lhs->astOperand1(), lhs->astOperand2()};
for (const Token *expr: exprTokens) {
if (lhs->str() == "-" && expr == lhs->astOperand2())
continue; // TODO?
// x + y cmp x
if (lhs->str() == "+" && other->varId() > 0) {
const std::string result = other->str() + cmp + "0";
integerOverflowOptimisationError(tok, result);
}
if (expr->hasKnownIntValue())
continue;
// x - y cmp x
if (lhs->str() == "-" && other->varId() > 0) {
std::string cmp2 = cmp;
cmp2[0] = (cmp[0] == '<') ? '>' : '<';
const std::string result = other->str() + cmp2 + "0";
integerOverflowOptimisationError(tok, result);
if (!isSameExpression(mTokenizer->isCPP(),
false,
expr,
lhs->astSibling(),
mSettings->library,
false,
false))
continue;
const Token * const other = expr->astSibling();
// x [+-] c cmp x
if (other->isNumber() && other->getKnownIntValue() > 0) {
bool result;
if (lhs->str() == "+")
result = (cmp == ">" || cmp == ">=");
else
result = (cmp == "<" || cmp == "<=");
integerOverflowOptimisationError(tok, result ? "true" : "false");
}
// x + y cmp x
if (lhs->str() == "+" && other->varId() > 0) {
const std::string result = other->str() + cmp + "0";
integerOverflowOptimisationError(tok, result);
}
// x - y cmp x
if (lhs->str() == "-" && other->varId() > 0) {
std::string cmp2 = cmp;
cmp2[0] = (cmp[0] == '<') ? '>' : '<';
const std::string result = other->str() + cmp2 + "0";
integerOverflowOptimisationError(tok, result);
}
}
}
}
}