Fixed #2097 (false positive: buffer access out of bounds)

lib/checkbufferoverrun.cpp

@@ -589,6 +589,10 @@ void CheckBufferOverrun::checkFunctionCall(const Token &tok, unsigned int par, c
 
                 if (ftok->varId() == parameterVarId)
                 {
+                    if (Token::Match(ftok->previous(), "-- %var%") ||
+                        Token::Match(ftok, "%var% --"))
+                        break;
+
                     if (Token::Match(ftok->previous(), "[=+-*/;{}] %var% [ %num% ]"))
                     {
                         long index = MathLib::toLongNumber(ftok->strAt(2));

test/testbufferoverrun.cpp

@@ -550,6 +550,20 @@ private:
               "    memclr( str, 5 );   // ERROR\n"
               "}\n");
         ASSERT_EQUALS("", errout.str());
+
+        // #2097..
+        check("void foo(int *p)\n"
+              "{\n"
+              "    --p;\n"
+              "    p[2] = 0;\n"
+              "}\n"
+              "\n"
+              "void bar()\n"
+              "{\n"
+              "    int p[3];\n"
+              "    foo(p+1);\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
     }