Fix #12117 FP integerOverflowCond for shift by 31 bits (#5596)

Author: chrchr-github

lib/checktype.cpp

@@ -205,8 +205,8 @@ void CheckType::checkIntegerOverflow()
             continue;
 
         // For left shift, it's common practice to shift into the sign bit
-        //if (tok->str() == "<<" && value->intvalue > 0 && value->intvalue < (((MathLib::bigint)1) << bits))
-        //    continue;
+        if (tok->str() == "<<" && value->intvalue > 0 && value->intvalue < (((MathLib::bigint)1) << bits))
+            continue;
 
         integerOverflowError(tok, *value);
     }

test/testtype.cpp

@@ -295,6 +295,11 @@ class TestType : public TestFixture {
               "   return 123456U * x;\n"
               "}",settings);
         ASSERT_EQUALS("", errout.str());
+
+        check("int f(int i) {\n" // #12117
+              "    return (i == 31) ? 1 << i : 0;\n"
+              "}", settings);
+        ASSERT_EQUALS("[test.cpp:2] -> [test.cpp:2]: (warning) Shifting signed 32-bit value by 31 bits is undefined behaviour. See condition at line 2.\n", errout.str());
     }
 
     void signConversion() {