Bug 579934 support constexpr evaluation of __builtin_ffs[l,ll]

Change-Id: I103a4d0a7958d6172eb2b05379c8eec40369526c

5 files changed, 138 insertions, 7 deletions

diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/GCCBuiltinSymbolProvider.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/GCCBuiltinSymbolProvider.java
index b453dfe5e10..b5ab4d3b5df 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/GCCBuiltinSymbolProvider.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/GCCBuiltinSymbolProvider.java
@@ -53,6 +53,8 @@ import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPImplicitTypedef;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPPointerType;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPQualifierType;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPReferenceType;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.ICPPExecution;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.ExecBuiltin;
 
 /**
  * This is the IBuiltinBindingsProvider used to implement the "Other" built-in GCC symbols defined:
@@ -188,6 +190,8 @@ public class GCCBuiltinSymbolProvider implements IBuiltinBindingsProvider {
 		function("bool", "__atomic_always_lock_free", "size_t", "void*");
 		function("bool", "__atomic_is_lock_free", "size_t", "void*");
 
+		ICPPExecution builtinFfs = new ExecBuiltin(ExecBuiltin.BUILTIN_FFS);
+
 		// Other Builtins (https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html) [incomplete]
 		function("void", "__builtin_abort");
 		function("int", "__builtin_abs", "int");
@@ -277,9 +281,9 @@ public class GCCBuiltinSymbolProvider implements IBuiltinBindingsProvider {
 		function("double", "__builtin_fdim", "double", "double");
 		function("float", "__builtin_fdimf", "float", "float");
 		function("long double", "__builtin_fdiml", "long double", "long double");
-		function("int", "__builtin_ffs", "unsigned int");
-		function("int", "__builtin_ffsl", "unsigned long");
-		function("int", "__builtin_ffsll", "unsigned long long");
+		function("int", "__builtin_ffs", builtinFfs, "unsigned int");
+		function("int", "__builtin_ffsl", builtinFfs, "unsigned long");
+		function("int", "__builtin_ffsll", builtinFfs, "unsigned long long");
 		function("double", "__builtin_floor", "double");
 		function("float", "__builtin_floorf", "float");
 		function("long double", "__builtin_floorl", "long double");
@@ -501,6 +505,13 @@ public class GCCBuiltinSymbolProvider implements IBuiltinBindingsProvider {
 	}
 
 	private void function(String returnType, String name, String... parameterTypes) {
+		function(returnType, name, null, parameterTypes);
+	}
+
+	/*
+	 * Create a function which can possibly be constexpr-evaluated
+	 */
+	private void function(String returnType, String name, ICPPExecution exec, String... parameterTypes) {
 		int len = parameterTypes.length;
 		boolean varargs = len > 0 && parameterTypes[len - 1].equals("...");
 		if (varargs)
@@ -511,14 +522,14 @@ public class GCCBuiltinSymbolProvider implements IBuiltinBindingsProvider {
 		for (int i = 0; i < len; i++) {
 			IType pType = toType(parameterTypes[i]);
 			pTypes[i] = pType;
-			theParms[i] = fCpp ? new CPPBuiltinParameter(pType) : new CBuiltinParameter(pType);
+			theParms[i] = fCpp ? new CPPBuiltinParameter(pType, i) : new CBuiltinParameter(pType);
 		}
 		IType rt = toType(returnType);
 		IFunctionType ft = fCpp ? new CPPFunctionType(rt, pTypes, null) : new CFunctionType(rt, pTypes);
 
 		IBinding b = fCpp
-				? new CPPImplicitFunction(toCharArray(name), fScope, (ICPPFunctionType) ft, (ICPPParameter[]) theParms,
-						false, varargs)
+				? new CPPBuiltinImplicitFunction(toCharArray(name), fScope, (ICPPFunctionType) ft,
+						(ICPPParameter[]) theParms, varargs, exec)
 				: new CImplicitFunction(toCharArray(name), fScope, ft, theParms, varargs);
 		fBindingList.add(b);
 	}
@@ -661,4 +672,22 @@ public class GCCBuiltinSymbolProvider implements IBuiltinBindingsProvider {
 	public boolean isKnownBuiltin(char[] builtinName) {
 		return fKnownBuiltins.containsKey(builtinName);
 	}
+
+	/*
+	 * A builtin function which can be evaluated in a constexpr context
+	 */
+	private static class CPPBuiltinImplicitFunction extends CPPImplicitFunction {
+		private ICPPExecution execution;
+
+		public CPPBuiltinImplicitFunction(char[] name, IScope scope, ICPPFunctionType type, ICPPParameter[] params,
+				boolean takesVarArgs, ICPPExecution execution) {
+			super(name, scope, type, params, true, takesVarArgs);
+			this.execution = execution;
+		}
+
+		@Override
+		public ICPPExecution getFunctionBodyExecution() {
+			return execution;
+		}
+	}
 }
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/ITypeMarshalBuffer.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/ITypeMarshalBuffer.java
index cc215747ed2..b7e352d7bf1 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/ITypeMarshalBuffer.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/ITypeMarshalBuffer.java
@@ -52,7 +52,7 @@ public interface ITypeMarshalBuffer {
 			EXEC_DECLARATION_STATEMENT = 0x05, EXEC_DECLARATOR = 0x06, EXEC_DEFAULT = 0x07,
 			EXEC_SIMPLE_DECLARATION = 0x08, EXEC_RETURN = 0x09, EXEC_EXPRESSION_STATEMENT = 0x0A, EXEC_IF = 0x0B,
 			EXEC_WHILE = 0x0C, EXEC_DO = 0x0D, EXEC_FOR = 0x0E, EXEC_RANGE_BASED_FOR = 0x0F, EXEC_SWITCH = 0x10,
-			EXEC_CONSTRUCTOR_CHAIN = 0x11, EXEC_INCOMPLETE = 0x12;
+			EXEC_CONSTRUCTOR_CHAIN = 0x11, EXEC_INCOMPLETE = 0x12, EXEC_BUILTIN = 0x13;
 	// Can add more executions up to 0x1C, after that it will collide with TypeMarshalBuffer.UNSTORABLE_TYPE.
 
 	static final short KIND_MASK = 0x001F;
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/CPPBuiltinParameter.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/CPPBuiltinParameter.java
index 3dd21dc3de9..754da65a108 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/CPPBuiltinParameter.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/CPPBuiltinParameter.java
@@ -38,9 +38,16 @@ public class CPPBuiltinParameter extends PlatformObject implements ICPPParameter
 	}
 
 	private IType type;
+	private int position;
 
 	public CPPBuiltinParameter(IType type) {
 		this.type = type;
+		this.position = -1;
+	}
+
+	public CPPBuiltinParameter(IType type, int position) {
+		this.type = type;
+		this.position = position;
 	}
 
 	@Override
@@ -75,6 +82,9 @@ public class CPPBuiltinParameter extends PlatformObject implements ICPPParameter
 
 	@Override
 	public String getName() {
+		if (position != -1) {
+			return "arg" + position; //$NON-NLS-1$
+		}
 		return ""; //$NON-NLS-1$
 	}
 
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/ExecBuiltin.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/ExecBuiltin.java
new file mode 100644
index 00000000000..338ef00240f
--- /dev/null
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/ExecBuiltin.java
@@ -0,0 +1,89 @@
+/*******************************************************************************
+* Copyright (c) 2022 Davin McCall and others.
+*
+* This program and the accompanying materials
+* are made available under the terms of the Eclipse Public License 2.0
+* which accompanies this distribution, and is available at
+* https://www.eclipse.org/legal/epl-2.0/
+*
+* SPDX-License-Identifier: EPL-2.0
+*
+* Contributors:
+*     Davin McCall - initial API and implementation
+*******************************************************************************/
+package org.eclipse.cdt.internal.core.dom.parser.cpp.semantics;
+
+import org.eclipse.cdt.core.dom.ast.IASTExpression.ValueCategory;
+import org.eclipse.cdt.core.dom.ast.IBasicType.Kind;
+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.cpp.CPPBasicType;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPBuiltinParameter;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.ICPPEvaluation;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.ICPPEvaluation.ConstexprEvaluationContext;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.ICPPExecution;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.InstantiationContext;
+import org.eclipse.core.runtime.CoreException;
+
+/**
+ * Constexpr-evaluation for compiler builtin functions.
+ */
+public class ExecBuiltin implements ICPPExecution {
+	public final static short BUILTIN_FFS = 0;
+
+	private static IType intType = new CPPBasicType(Kind.eInt, 0);
+
+	private short funcId;
+
+	public ExecBuiltin(short funcId) {
+		this.funcId = funcId;
+	}
+
+	@Override
+	public ICPPExecution instantiate(InstantiationContext context, int maxDepth) {
+		return this;
+	}
+
+	@Override
+	public ICPPExecution executeForFunctionCall(ActivationRecord record, ConstexprEvaluationContext context) {
+
+		switch (funcId) {
+		case BUILTIN_FFS:
+			return executeBuiltinFfs(record, context);
+		}
+		return null;
+	}
+
+	private ICPPExecution executeBuiltinFfs(ActivationRecord record, ConstexprEvaluationContext context) {
+		ICPPEvaluation arg0 = record.getVariable(new CPPBuiltinParameter(null, 0));
+
+		IValue argValue = arg0.getValue();
+		if (!(argValue instanceof IntegralValue))
+			return null;
+
+		// __builtin_ffs returns 0 if arg is 0, or 1+count where count is the number of trailing 0 bits
+		long arg = argValue.numberValue().longValue();
+		if (arg == 0) {
+			return new ExecReturn(new EvalFixed(intType, ValueCategory.PRVALUE, IntegralValue.create(0)));
+		}
+		int count = 0;
+		while ((arg & 1) == 0) {
+			arg >>= 1;
+			count++;
+		}
+		return new ExecReturn(new EvalFixed(intType, ValueCategory.PRVALUE, IntegralValue.create(count + 1)));
+	}
+
+	@Override
+	public void marshal(ITypeMarshalBuffer buffer, boolean includeValue) throws CoreException {
+		buffer.putShort(ITypeMarshalBuffer.EXEC_BUILTIN);
+		buffer.putShort(funcId);
+	}
+
+	public static ICPPExecution unmarshal(short firstBytes, ITypeMarshalBuffer buffer) throws CoreException {
+		short funcId = buffer.getShort();
+		return new ExecBuiltin(funcId);
+	}
+}
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/dom/cpp/PDOMCPPLinkage.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/dom/cpp/PDOMCPPLinkage.java
index 9b683b08a2e..991f3ef73eb 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/dom/cpp/PDOMCPPLinkage.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/dom/cpp/PDOMCPPLinkage.java
@@ -143,6 +143,7 @@ import org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.EvalTypeId;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.EvalUnary;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.EvalUnaryTypeID;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.ExecBreak;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.ExecBuiltin;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.ExecCase;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.ExecCompoundStatement;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.ExecConstructorChain;
@@ -1771,6 +1772,8 @@ class PDOMCPPLinkage extends PDOMLinkage implements IIndexCPPBindingConstants {
 			return ExecConstructorChain.unmarshal(firstBytes, buffer);
 		case ITypeMarshalBuffer.EXEC_INCOMPLETE:
 			return ExecIncomplete.unmarshal(firstBytes, buffer);
+		case ITypeMarshalBuffer.EXEC_BUILTIN:
+			return ExecBuiltin.unmarshal(firstBytes, buffer);
 		}
 		throw new CoreException(CCorePlugin.createStatus("Cannot unmarshal an execution, first bytes=" + firstBytes)); //$NON-NLS-1$
 	}