Fix #15032 FP knownConditionTrueFalse for bitwise negation of char (#8941)

Author: chrchr-github

lib/valueflow.cpp

@@ -4131,7 +4131,7 @@ static std::list<ValueFlow::Value> truncateValues(std::list<ValueFlow::Value> va
         }
 
         if (value.isIntValue() && sz > 0 && sz < sizeof(MathLib::biguint))
-            value.intvalue = ValueFlow::truncateIntValue(value.intvalue, sz, dst->sign);
+            value.intvalue = ValueFlow::truncateIntValue(value.intvalue, sz, dst, settings.platform);
     }
     return values;
 }

lib/vf_analyzers.cpp

@@ -357,7 +357,7 @@ struct ValueFlowAnalyzer : Analyzer {
             if (dst) {
                 const size_t sz = dst->getSizeOf(settings, ValueType::Accuracy::ExactOrZero, ValueType::SizeOf::Pointer);
                 if (sz > 0 && sz < sizeof(MathLib::biguint)) {
-                    MathLib::bigint newvalue = ValueFlow::truncateIntValue(value->intvalue, sz, dst->sign);
+                    MathLib::bigint newvalue = ValueFlow::truncateIntValue(value->intvalue, sz, dst, settings.platform);
 
                     /* Handle overflow/underflow for value bounds */
                     if (value->bound != ValueFlow::Value::Bound::Point) {

lib/vf_common.cpp

@@ -96,15 +96,15 @@ namespace ValueFlow
         return true;
     }
 
-    MathLib::bigint truncateIntValue(MathLib::bigint value, size_t value_size, const ValueType::Sign dst_sign)
+    MathLib::bigint truncateIntValue(MathLib::bigint value, size_t value_size, const ValueType* dst, const Platform& platform)
     {
         if (value_size == 0)
             return value;
 
         const MathLib::biguint unsignedMaxValue = std::numeric_limits<MathLib::biguint>::max() >> ((sizeof(unsignedMaxValue) - value_size) * 8);
         const MathLib::biguint signBit = 1ULL << ((value_size * 8) - 1);
         value &= unsignedMaxValue;
-        if (dst_sign == ValueType::Sign::SIGNED && (value & signBit))
+        if ((dst->sign == ValueType::Sign::SIGNED || (dst->sign == ValueType::Sign::UNKNOWN_SIGN && dst->type == ValueType::Type::CHAR && platform.defaultSign == 's')) && (value & signBit))
             value |= ~unsignedMaxValue;
 
         return value;

lib/vf_common.h

@@ -41,7 +41,7 @@ namespace ValueFlow
 {
     bool getMinMaxValues(const ValueType* vt, const Platform& platform, MathLib::bigint& minValue, MathLib::bigint& maxValue);
 
-    MathLib::bigint truncateIntValue(MathLib::bigint value, size_t value_size, ValueType::Sign dst_sign);
+    MathLib::bigint truncateIntValue(MathLib::bigint value, size_t value_size, const ValueType* dst, const Platform& platform);
 
     Token * valueFlowSetConstantValue(Token *tok, const Settings &settings);
 

lib/vf_settokenvalue.cpp

@@ -665,7 +665,7 @@ namespace ValueFlow
                         const ValueType *dst = tok->valueType();
                         if (dst) {
                             const size_t sz = dst->getSizeOf(settings, ValueType::Accuracy::ExactOrZero, ValueType::SizeOf::Pointer);
-                            MathLib::bigint newvalue = ValueFlow::truncateIntValue(v.intvalue + 1, sz, dst->sign);
+                            MathLib::bigint newvalue = ValueFlow::truncateIntValue(v.intvalue + 1, sz, dst, settings.platform);
                             if (v.bound != ValueFlow::Value::Bound::Point) {
                                 if (newvalue < v.intvalue) {
                                     v.invertBound();
@@ -695,7 +695,7 @@ namespace ValueFlow
                         const ValueType *dst = tok->valueType();
                         if (dst) {
                             const size_t sz = dst->getSizeOf(settings, ValueType::Accuracy::ExactOrZero, ValueType::SizeOf::Pointer);
-                            MathLib::bigint newvalue = ValueFlow::truncateIntValue(v.intvalue - 1, sz, dst->sign);
+                            MathLib::bigint newvalue = ValueFlow::truncateIntValue(v.intvalue - 1, sz, dst, settings.platform);
                             if (v.bound != ValueFlow::Value::Bound::Point) {
                                 if (newvalue > v.intvalue) {
                                     v.invertBound();

test/testvalueflow.cpp

@@ -1389,6 +1389,13 @@ class TestValueFlow : public TestFixture {
             ASSERT_EQUALS(22, values.back().intvalue);
         }
 
+        code  = "void f() {\n" // #15032
+                "    char c = -1;\n"
+                "    if (~c == -256) {}\n"
+                "}\n";
+        const int expected = std::numeric_limits<char>::is_signed ? 0 : -256;
+        ASSERT_EQUALS(true, testKnownValueOfTok(code, "~", expected));
+
         // #10251 starship operator
         code  = "struct X {};\n"
                 "auto operator<=>(const X & a, const X & b) -> decltype(1 <=> 2) {\n"