Bug 394521 Do Constant folding propagation when building CFG

When building control flow graph we can consider constants
and not add some branches in decisions nodes, that make CFG
more accurate and elimate some false positives

Change-Id: I19c623e1e6d2dc7416a0e796a98168df7a976111
Signed-off-by: Alena Laskavaia <elaskavaia.cdt@gmail.com>
Reviewed-on: https://git.eclipse.org/r/28726

3 files changed, 94 insertions, 5 deletions

diff --git a/codan/org.eclipse.cdt.codan.core.cxx/src/org/eclipse/cdt/codan/core/cxx/internal/model/cfg/ControlFlowGraphBuilder.java b/codan/org.eclipse.cdt.codan.core.cxx/src/org/eclipse/cdt/codan/core/cxx/internal/model/cfg/ControlFlowGraphBuilder.java
index 69809d2ae60..139b4af08b2 100644
--- a/codan/org.eclipse.cdt.codan.core.cxx/src/org/eclipse/cdt/codan/core/cxx/internal/model/cfg/ControlFlowGraphBuilder.java
+++ b/codan/org.eclipse.cdt.codan.core.cxx/src/org/eclipse/cdt/codan/core/cxx/internal/model/cfg/ControlFlowGraphBuilder.java
@@ -52,8 +52,10 @@ import org.eclipse.cdt.core.dom.ast.IASTStatement;
 import org.eclipse.cdt.core.dom.ast.IASTSwitchStatement;
 import org.eclipse.cdt.core.dom.ast.IASTUnaryExpression;
 import org.eclipse.cdt.core.dom.ast.IASTWhileStatement;
+import org.eclipse.cdt.core.dom.ast.IValue;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTCatchHandler;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTTryBlockStatement;
+import org.eclipse.cdt.internal.core.dom.parser.Value;
 
 /**
  * This class creates C control flow graph
@@ -463,14 +465,37 @@ public class ControlFlowGraphBuilder {
 		if (prev instanceof IExitNode || prev == null) {
 			dead.add(node);
 			return;
-		} else if (prev instanceof ICfgData) {
-			if (prev instanceof IDecisionNode && !(node instanceof IBranchNode)) {
+		}
+		if (prev instanceof IDecisionNode) {
+			if (node instanceof IBranchNode) {
+				IDecisionNode decisionNode = (IDecisionNode) prev;
+				if (isConstant(decisionNode, 1) && ((IBranchNode) node).getLabel().equals(IBranchNode.ELSE)) {
+					dead.add(node);
+					return;
+				} else if (isConstant(decisionNode, 0) && ((IBranchNode) node).getLabel().equals(IBranchNode.THEN)) {
+					dead.add(node);
+					return;
+				}
+			} else {
 				dead.add(node);
 				return;
 			}
-			((AbstractBasicBlock) prev).addOutgoing(node);
 		}
+		((AbstractBasicBlock) prev).addOutgoing(node);
 		if (!(node instanceof IStartNode))
 			((AbstractBasicBlock) node).addIncoming(prev);
 	}
+
+	private boolean isConstant(IDecisionNode node, long testvalue) {
+		if (node instanceof ICfgData) {
+			IASTNode ast = (IASTNode) ((ICfgData) node).getData();
+			if (ast instanceof IASTExpression) {
+				IValue dvalue = Value.create((IASTExpression) ast, 5);
+				Long numericalValue = dvalue.numericalValue();
+				if (numericalValue==null) return false;
+				return (numericalValue==testvalue);
+			}
+		}
+		return false;
+	}
 }
diff --git a/codan/org.eclipse.cdt.codan.core.test/src/org/eclipse/cdt/codan/core/cfg/ControlFlowGraphTest.java b/codan/org.eclipse.cdt.codan.core.test/src/org/eclipse/cdt/codan/core/cfg/ControlFlowGraphTest.java
index dd6c6d20592..d483f52b425 100644
--- a/codan/org.eclipse.cdt.codan.core.test/src/org/eclipse/cdt/codan/core/cfg/ControlFlowGraphTest.java
+++ b/codan/org.eclipse.cdt.codan.core.test/src/org/eclipse/cdt/codan/core/cfg/ControlFlowGraphTest.java
@@ -294,8 +294,8 @@ public class ControlFlowGraphTest extends CodanFastCxxAstTestCase {
 		assertEquals(1, graph.getUnconnectedNodeSize());
 	}
 
-	//	 foo() {
-	//	   int a=10, x=5;
+	//	 foo(int x) {
+	//	   int a=10;
 	//	   if (a--) {
 	//	      if (x<0)
 	//	         a++;
@@ -408,4 +408,46 @@ public class ControlFlowGraphTest extends CodanFastCxxAstTestCase {
 		IStartNode startNode = graph.getStartNode();
 		assertEquals(1, graph.getUnconnectedNodeSize());
 	}
+
+	//	 foo() {
+	//	   int a=10,x=5;
+	//	   if (x<0)
+	//	       a++;
+	//	 }
+	public void test_deadbranch() {
+		buildCfg(getAboveComment(), false);
+		checkCfg(false);
+		IStartNode startNode = graph.getStartNode();
+		IPlainNode decl = (IPlainNode) startNode.getOutgoing();
+		IDecisionNode des = (IDecisionNode) decl.getOutgoing();
+		assertEquals("x<0", data(des));
+		IBasicBlock bElse = branchEnd(des, IBranchNode.ELSE);
+		IBasicBlock m2 = jumpEnd(branchEnd(des, IBranchNode.THEN));
+		IBasicBlock m1 = jumpEnd(bElse);
+
+		assertNull(m2);
+		assertNotNull(m1);
+	}
+
+//	int test1_f()
+//	{
+//	    while (1)
+//	    {
+//	    }
+//	}
+	public void test_infiniloop() {
+		buildCfg(getAboveComment(), false);
+		checkCfg(false);
+		IStartNode startNode = graph.getStartNode();
+		IConnectorNode conn = (IConnectorNode) startNode.getOutgoing();
+		IDecisionNode des = (IDecisionNode) conn.getOutgoing();
+		assertEquals("1", data(des));
+		IBasicBlock bElse = branchEnd(des, IBranchNode.ELSE);
+		IBasicBlock bThen = branchEnd(des, IBranchNode.THEN);
+		IBasicBlock m2 = jumpEnd(bThen);
+		IBasicBlock m1 = jumpEnd(bElse);
+
+		assertNotNull(m2);
+		assertNull(m1);
+	}
 }
diff --git a/codan/org.eclipse.cdt.codan.core.test/src/org/eclipse/cdt/codan/core/internal/checkers/ReturnCheckerTest.java b/codan/org.eclipse.cdt.codan.core.test/src/org/eclipse/cdt/codan/core/internal/checkers/ReturnCheckerTest.java
index d56ff169f05..e1e1f1775c1 100644
--- a/codan/org.eclipse.cdt.codan.core.test/src/org/eclipse/cdt/codan/core/internal/checkers/ReturnCheckerTest.java
+++ b/codan/org.eclipse.cdt.codan.core.test/src/org/eclipse/cdt/codan/core/internal/checkers/ReturnCheckerTest.java
@@ -384,4 +384,26 @@ public class ReturnCheckerTest extends CheckerTestCase {
 		checkNoErrors();
 	}
 
+//	int test1() {
+//	    do {
+//	        return 1;
+//	    } while (0);
+//	}
+	public void testNoRetInfinitLoop() throws Exception {
+		// Bug 394521
+		loadCodeAndRunCpp(getAboveComment());
+		checkNoErrors();
+	}
+
+//	int test1_f()    // WARNING HERE: "No return, in function returning non-void"
+//	{
+//	    while (1)
+//	    {
+//	    }
+//	}
+	public void testNoRetInfinitLoop2() throws Exception {
+		// Bug 394521
+		loadCodeAndRunCpp(getAboveComment());
+		checkNoErrors();
+	}
 }
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