simplifyNumericCalculations: Don't fold negative constants in shift/bitmask calculation. Behaviour is not well defined.

danmar · danmar · commit 1977a18a1ecd · 2015-11-27T14:16:49.000+01:00
diff --git a/lib/templatesimplifier.cpp b/lib/templatesimplifier.cpp
@@ -964,6 +964,12 @@ bool TemplateSimplifier::simplifyNumericCalculations(Token *tok)
 
         // Integer operations
         if (Token::Match(op, ">>|<<|&|^|%or%")) {
+            // Don't simplify if operand is negative, shifting with negative
+            // operand is UB. Bitmasking with negative operand is implementation
+            // defined behaviour.
+            if (MathLib::isNegative(tok->str()) || MathLib::isNegative(tok->strAt(2)))
+                continue;
+
             const char cop = op->str()[0];
             std::string result;
             if (tok->str().find_first_of("uU") != std::string::npos)
diff --git a/test/testsimplifytokens.cpp b/test/testsimplifytokens.cpp
@@ -2096,6 +2096,7 @@ class TestSimplifyTokens : public TestFixture {
         ASSERT_EQUALS("x ( 1 )", tok("x(2 && 4<<4<<5 && 4)")); // #4933
         ASSERT_EQUALS("x ( 1 )", tok("x(9&&8%5%4/3)")); // #4931
         ASSERT_EQUALS("x ( 1 )", tok("x(2 && 2|5<<2%4)")); // #4931
+        ASSERT_EQUALS("x ( -2 << 6 | 1 )", tok("x(1-3<<6|5/3)")); // #4931
 
         // don't remove these spaces..
         ASSERT_EQUALS("new ( auto ) ( 4 ) ;", tok("new (auto)(4);"));
