Bug 580325 - constexpr evaluation of builtins for clrsb, clz (#52)

Adds constexpr evaluation for some additional compiler builtins. This is
probably the last lot few builtins that can reasonably be
constexpr-evaluated in CDT.

core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/cxx14/constexpr/IntegralValueTests.java

@@ -340,4 +340,24 @@ public abstract class IntegralValueTests extends TestBase {
 	public void testBuiltinAbsNarrowing() throws Exception {
 		assertEvaluationEquals(1);
 	}
+
+	// constexpr int x = __builtin_clrsb(0xFFFFFFFF);
+	public void testBuiltinClrsb() throws Exception {
+		assertEvaluationEquals(31);
+	}
+
+	// constexpr int x = __builtin_clrsb(555);
+	public void testBuiltinClrsbPositive() throws Exception {
+		assertEvaluationEquals(21);
+	}
+
+	// constexpr int x = __builtin_clz(0x8000);
+	public void testBuiltinClz() throws Exception {
+		assertEvaluationEquals(16);
+	}
+
+	// constexpr int x = __builtin_clz(-17);
+	public void testBuiltinClzNegative() throws Exception {
+		assertEvaluationEquals(0);
+	}
 }

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/GCCBuiltinSymbolProvider.java

@@ -205,6 +205,12 @@ public class GCCBuiltinSymbolProvider implements IBuiltinBindingsProvider {
 		ICPPExecution builtinAbs = new ExecBuiltin(ExecBuiltin.BUILTIN_ABS);
 		ICPPExecution builtinLabs = new ExecBuiltin(ExecBuiltin.BUILTIN_LABS);
 		ICPPExecution builtinLlabs = new ExecBuiltin(ExecBuiltin.BUILTIN_LLABS);
+		ICPPExecution builtinClrsb = new ExecBuiltin(ExecBuiltin.BUILTIN_CLRSB);
+		ICPPExecution builtinClrsbl = new ExecBuiltin(ExecBuiltin.BUILTIN_CLRSBL);
+		ICPPExecution builtinClrsbll = new ExecBuiltin(ExecBuiltin.BUILTIN_CLRSBLL);
+		ICPPExecution builtinClz = new ExecBuiltin(ExecBuiltin.BUILTIN_CLZ);
+		ICPPExecution builtinClzl = new ExecBuiltin(ExecBuiltin.BUILTIN_CLZL);
+		ICPPExecution builtinClzll = new ExecBuiltin(ExecBuiltin.BUILTIN_CLZLL);
 
 		// Other Builtins (https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html) [incomplete]
 		function("void", "__builtin_abort");
@@ -243,12 +249,12 @@ public class GCCBuiltinSymbolProvider implements IBuiltinBindingsProvider {
 		function("float", "__builtin_cimagf", "complex float");
 		function("long double", "__builtin_cimagl", "complex long double");
 		function("void", "__builtin___clear_cache", "void*", "void*");
-		function("int", "__builtin_clrsb", "int");
+		function("int", "__builtin_clrsb", builtinClrsb, "int");
-		function("int", "__builtin_clrsbl", "long");
+		function("int", "__builtin_clrsbl", builtinClrsbl, "long");
-		function("int", "__builtin_clrsbll", "long long");
+		function("int", "__builtin_clrsbll", builtinClrsbll, "long long");
-		function("int", "__builtin_clz", "unsigned int");
+		function("int", "__builtin_clz", builtinClz, "unsigned int");
-		function("int", "__builtin_clzl", "unsigned long");
+		function("int", "__builtin_clzl", builtinClzl, "unsigned long");
-		function("int", "__builtin_clzll", "unsigned long long");
+		function("int", "__builtin_clzll", builtinClzll, "unsigned long long");
 		function("complex double", "__builtin_conj", "complex double");
 		function("complex float", "__builtin_conjf", "complex float");
 		function("complex long double", "__builtin_conjl", "complex long double");
@@ -330,7 +336,7 @@ public class GCCBuiltinSymbolProvider implements IBuiltinBindingsProvider {
 		function("int", "__builtin_ilogb", "double");
 		function("int", "__builtin_ilogbf", "float");
 		function("int", "__builtin_ilogbl", "long double");
-		function("long long", "__builtin_imaxabs", "long long");
+		function("long long", "__builtin_imaxabs", builtinLlabs, "long long");
 		function("double", "__builtin_inf");
 		function("_Decimal32", "__builtin_infd32");
 		function("_Decimal64", "__builtin_infd64");

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/ExecBuiltin.java

@@ -19,6 +19,8 @@ import org.eclipse.cdt.core.dom.ast.IType;
 import org.eclipse.cdt.core.dom.ast.IValue;
 import org.eclipse.cdt.internal.core.dom.parser.ITypeMarshalBuffer;
 import org.eclipse.cdt.internal.core.dom.parser.IntegralValue;
+import org.eclipse.cdt.internal.core.dom.parser.SizeofCalculator;
+import org.eclipse.cdt.internal.core.dom.parser.SizeofCalculator.SizeAndAlignment;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPBasicType;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPBuiltinParameter;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.ICPPEvaluation;
@@ -33,7 +35,9 @@ import org.eclipse.core.runtime.CoreException;
 public class ExecBuiltin implements ICPPExecution {
 	public final static short BUILTIN_FFS = 0, BUILTIN_FFSL = 1, BUILTIN_FFSLL = 2, BUILTIN_CTZ = 3, BUILTIN_CTZL = 4,
 			BUILTIN_CTZLL = 5, BUILTIN_POPCOUNT = 6, BUILTIN_POPCOUNTL = 7, BUILTIN_POPCOUNTLL = 8, BUILTIN_PARITY = 9,
-			BUILTIN_PARITYL = 10, BUILTIN_PARITYLL = 11, BUILTIN_ABS = 12, BUILTIN_LABS = 13, BUILTIN_LLABS = 14;
+			BUILTIN_PARITYL = 10, BUILTIN_PARITYLL = 11, BUILTIN_ABS = 12, BUILTIN_LABS = 13, BUILTIN_LLABS = 14,
+			BUILTIN_CLRSB = 15, BUILTIN_CLRSBL = 16, BUILTIN_CLRSBLL = 17, BUILTIN_CLZ = 18, BUILTIN_CLZL = 19,
+			BUILTIN_CLZLL = 20;
 
 	private static IType intType = new CPPBasicType(Kind.eInt, 0);
 	private static IType longType = new CPPBasicType(Kind.eInt, CPPBasicType.IS_LONG);
@@ -84,6 +88,18 @@ public class ExecBuiltin implements ICPPExecution {
 			return executeBuiltinAbs(record, context, longType);
 		case BUILTIN_LLABS:
 			return executeBuiltinAbs(record, context, longlongType);
+		case BUILTIN_CLRSB:
+			return executeBuiltinClrsb(record, context, intType);
+		case BUILTIN_CLRSBL:
+			return executeBuiltinClrsb(record, context, longType);
+		case BUILTIN_CLRSBLL:
+			return executeBuiltinClrsb(record, context, longlongType);
+		case BUILTIN_CLZ:
+			return executeBuiltinClz(record, context, intType);
+		case BUILTIN_CLZL:
+			return executeBuiltinClz(record, context, longType);
+		case BUILTIN_CLZLL:
+			return executeBuiltinClz(record, context, longlongType);
 		}
 		return null;
 	}
@@ -166,6 +182,9 @@ public class ExecBuiltin implements ICPPExecution {
 		return executeBuiltinPopcountParity(record, context, true, argType);
 	}
 
+	/*
+	 * Return an execution implementing __builtin_abs
+	 */
 	private ICPPExecution executeBuiltinAbs(ActivationRecord record, ConstexprEvaluationContext context,
 			IType argType) {
 		ICPPEvaluation arg0 = record.getVariable(new CPPBuiltinParameter(null, 0));
@@ -182,6 +201,69 @@ public class ExecBuiltin implements ICPPExecution {
 		return new ExecReturn(new EvalFixed(argType, ValueCategory.PRVALUE, IntegralValue.create(result)));
 	}
 
+	/*
+	 * Return an execution implementing __builtin_clsrb (count leading "redundant" sign bits)
+	 */
+	private ICPPExecution executeBuiltinClrsb(ActivationRecord record, ConstexprEvaluationContext context,
+			IType argType) {
+		ICPPEvaluation arg0 = record.getVariable(new CPPBuiltinParameter(null, 0));
+
+		SizeAndAlignment sizeToType = SizeofCalculator.getSizeAndAlignment(argType);
+		if (sizeToType.size > 8)
+			return null; // can't handle too-large type
+
+		IValue argValue = arg0.getValue();
+		Number argNumber = argValue.numberValue();
+		if (argNumber == null)
+			return null;
+
+		long argLong = argNumber.longValue();
+		long signBit = 1L << (sizeToType.size * 8 - 1);
+		int result = 0;
+		long valueBit = signBit >>> 1;
+
+		if ((argLong & signBit) == 0) {
+			// if positive, invert all bits so we can unconditionally count 1 bits
+			argLong = ~argLong;
+		}
+
+		while ((argLong & valueBit) != 0) {
+			result++;
+			valueBit >>>= 1;
+		}
+
+		return new ExecReturn(new EvalFixed(intType, ValueCategory.PRVALUE, IntegralValue.create(result)));
+	}
+
+	private ICPPExecution executeBuiltinClz(ActivationRecord record, ConstexprEvaluationContext context,
+			IType argType) {
+		ICPPEvaluation arg0 = record.getVariable(new CPPBuiltinParameter(null, 0));
+
+		SizeAndAlignment sizeToType = SizeofCalculator.getSizeAndAlignment(argType);
+		if (sizeToType.size > 8)
+			return null; // can't handle too-large type
+
+		IValue argValue = arg0.getValue();
+		Number argNumber = argValue.numberValue();
+		if (argNumber == null)
+			return null;
+
+		long argLong = argNumber.longValue();
+		long valueBit = 1L << (sizeToType.size * 8 - 1);
+		int result = 0;
+
+		// Note that __builtin_clz(0) is supposedly undefined, but GCC (12.1) apparently returns
+		// the bit size of int, so we'll make sure to do the same.
+		while ((argLong & valueBit) == 0) {
+			result++;
+			valueBit >>>= 1;
+			if (valueBit == 0)
+				break;
+		}
+
+		return new ExecReturn(new EvalFixed(intType, ValueCategory.PRVALUE, IntegralValue.create(result)));
+	}
+
 	@Override
 	public void marshal(ITypeMarshalBuffer buffer, boolean includeValue) throws CoreException {
 		buffer.putShort(ITypeMarshalBuffer.EXEC_BUILTIN);