Improve isSameExpression for literals (#2514)

Improve isSameExpression() for literals with same value but different
representation, for example  the following different ways of
representing 9 as double: 9.0, 0.9e1 and 0x1.2p3.

With this change, cppcheck can (for example) correctly detect that the
else if statements are always false in the following example:

	void f(double x) {
		if (x < 9.0) {}
		else if (x < 0x1.2p3) {}
		else if (x < 0.9e1) {}
	}

Author: rikardfalkeborn

lib/astutils.cpp

@@ -547,6 +547,26 @@ bool isDifferentKnownValues(const Token * const tok1, const Token * const tok2)
     return result;
 }
 
+static bool isSameConstantValue(bool macro, const Token * const tok1, const Token * const tok2)
+{
+    if (tok1 == nullptr || tok2 == nullptr)
+        return false;
+
+    if (!tok1->isNumber() || !tok2->isNumber())
+        return false;
+
+    if (macro && (tok1->isExpandedMacro() || tok2->isExpandedMacro() || tok1->isTemplateArg() || tok2->isTemplateArg()))
+        return false;
+
+    const ValueType * v1 = tok1->valueType();
+    const ValueType * v2 = tok2->valueType();
+
+    if (!v1 || !v2 || v1->sign != v2->sign || v1->type != v2->type || v1->pointer != v2->pointer)
+        return false;
+
+    return isEqualKnownValue(tok1, tok2);
+}
+
 bool isSameExpression(bool cpp, bool macro, const Token *tok1, const Token *tok2, const Library& library, bool pure, bool followVar, ErrorPath* errors)
 {
     if (tok1 == nullptr && tok2 == nullptr)
@@ -568,6 +588,9 @@ bool isSameExpression(bool cpp, bool macro, const Token *tok1, const Token *tok2
     }
     if (tok1->str() != tok2->str() && isDifferentKnownValues(tok1, tok2))
         return false;
+    if (isSameConstantValue(macro, tok1, tok2))
+        return true;
+
     // Follow variable
     if (followVar && tok1->str() != tok2->str() && (Token::Match(tok1, "%var%") || Token::Match(tok2, "%var%"))) {
         const Token * varTok1 = followVariableExpression(tok1, cpp, tok2);

test/testastutils.cpp

@@ -36,6 +36,7 @@ class TestAstUtils : public TestFixture {
         TEST_CASE(findLambdaEndToken);
         TEST_CASE(findLambdaStartToken);
         TEST_CASE(isReturnScope);
+        TEST_CASE(isSameExpression);
         TEST_CASE(isVariableChanged);
         TEST_CASE(isVariableChangedByFunctionCall);
         TEST_CASE(nextAfterAstRightmostLeaf);
@@ -135,6 +136,33 @@ class TestAstUtils : public TestFixture {
         ASSERT_EQUALS(true, isReturnScope("void positiveTokenOffset() { return; }", 7));
     }
 
+    bool isSameExpression(const char code[], const char tokStr1[], const char tokStr2[]) {
+        Settings settings;
+        Library library;
+        Tokenizer tokenizer(&settings, this);
+        std::istringstream istr(code);
+        tokenizer.tokenize(istr, "test.cpp");
+        const Token * const tok1 = Token::findsimplematch(tokenizer.tokens(), tokStr1);
+        const Token * const tok2 = Token::findsimplematch(tok1->next(), tokStr2);
+        return ::isSameExpression(false, false, tok1, tok2, library, false, false, nullptr);
+    }
+
+    void isSameExpression() {
+        ASSERT_EQUALS(true,  isSameExpression("x = 1 + 1;", "1", "1"));
+        ASSERT_EQUALS(false, isSameExpression("x = 1 + 1u;", "1", "1u"));
+        ASSERT_EQUALS(true,  isSameExpression("x = 1.0 + 1.0;", "1.0", "1.0"));
+        ASSERT_EQUALS(false, isSameExpression("x = 1.0f + 1.0;", "1.0f", "1.0"));
+        ASSERT_EQUALS(false, isSameExpression("x = 1L + 1;", "1L", "1"));
+        ASSERT_EQUALS(true,  isSameExpression("x = 0.0f + 0x0p+0f;", "0.0f", "0x0p+0f"));
+        ASSERT_EQUALS(true,  isSameExpression("x < x;", "x", "x"));
+        ASSERT_EQUALS(false, isSameExpression("x < y;", "x", "y"));
+        ASSERT_EQUALS(true,  isSameExpression("(x + 1) < (x + 1);", "+", "+"));
+        ASSERT_EQUALS(false, isSameExpression("(x + 1) < (x + 1L);", "+", "+"));
+        ASSERT_EQUALS(true,  isSameExpression("(1 + x) < (x + 1);", "+", "+"));
+        ASSERT_EQUALS(false, isSameExpression("(1.0l + x) < (1.0 + x);", "+", "+"));
+        ASSERT_EQUALS(true,  isSameExpression("(0.0 + x) < (x + 0x0p+0);", "+", "+"));
+    }
+
     bool isVariableChanged(const char code[], const char startPattern[], const char endPattern[]) {
         Settings settings;
         Tokenizer tokenizer(&settings, this);