Fix #11591 Truncate variable after pre/post increment operator (#6331)

Author: francois-berder

lib/valueflow.cpp

@@ -604,6 +604,17 @@ static ValueFlow::Value truncateImplicitConversion(Token* parent, const ValueFlo
     return v;
 }
 
+static long long truncateIntValue(long long value, size_t value_size, const ValueType::Sign dst_sign)
+{
+    const MathLib::biguint unsignedMaxValue = (1ULL << (value_size * 8)) - 1ULL;
+    const MathLib::biguint signBit = 1ULL << (value_size * 8 - 1);
+    value &= unsignedMaxValue;
+    if (dst_sign == ValueType::Sign::SIGNED && (value & signBit))
+        value |= ~unsignedMaxValue;
+
+    return value;
+}
+
 /** set ValueFlow value and perform calculations if possible */
 static void setTokenValue(Token* tok,
                           ValueFlow::Value value,
@@ -2817,7 +2828,16 @@ struct ValueFlowAnalyzer : Analyzer {
             if (d == Direction::Reverse)
                 inc = !inc;
             value->intvalue += (inc ? 1 : -1);
-            value->errorPath.emplace_back(tok, tok->str() + " is " + opName + "', new value is " + value->infoString());
+
+            /* Truncate value */
+            const ValueType *dst = tok->valueType();
+            if (dst) {
+                const size_t sz = ValueFlow::getSizeOf(*dst, settings);
+                if (sz > 0 && sz < 8)
+                    value->intvalue = truncateIntValue(value->intvalue, sz, dst->sign);
+
+                value->errorPath.emplace_back(tok, tok->str() + " is " + opName + "', new value is " + value->infoString());
+            }
         }
     }
 
@@ -6028,13 +6048,8 @@ static std::list<ValueFlow::Value> truncateValues(std::list<ValueFlow::Value> va
             value.valueType = ValueFlow::Value::ValueType::INT;
         }
 
-        if (value.isIntValue() && sz > 0 && sz < 8) {
-            const MathLib::biguint unsignedMaxValue = (1ULL << (sz * 8)) - 1ULL;
-            const MathLib::biguint signBit = 1ULL << (sz * 8 - 1);
-            value.intvalue &= unsignedMaxValue;
-            if (dst->sign == ValueType::Sign::SIGNED && (value.intvalue & signBit))
-                value.intvalue |= ~unsignedMaxValue;
-        }
+        if (value.isIntValue() && sz > 0 && sz < 8)
+            value.intvalue = truncateIntValue(value.intvalue, sz, dst->sign);
     }
     return values;
 }

test/testvalueflow.cpp

@@ -150,6 +150,7 @@ class TestValueFlow : public TestFixture {
         TEST_CASE(valueFlowIdempotent);
         TEST_CASE(valueFlowUnsigned);
         TEST_CASE(valueFlowMod);
+        TEST_CASE(valueFlowInc);
         TEST_CASE(valueFlowNotNull);
         TEST_CASE(valueFlowSymbolic);
         TEST_CASE(valueFlowSymbolicIdentity);
@@ -7879,6 +7880,22 @@ class TestValueFlow : public TestFixture {
         ASSERT_EQUALS(false, testValueOfXImpossible(code, 3U, 1));
     }
 
+    void valueFlowInc() {
+        const char *code;
+        std::list<ValueFlow::Value> values;
+
+        // #11591
+        code = "int f() {\n"
+               "    const int a[1] = {};\n"
+               "    unsigned char i = 255;\n"
+               "    ++i;\n"
+               "    return a[i];\n"
+               "}\n";
+        values = tokenValues(code, "i ]");
+        ASSERT_EQUALS(1U, values.size());
+        ASSERT_EQUALS(0LLU, values.back().intvalue);
+    }
+
     void valueFlowNotNull()
     {
         const char* code;