C++: Support C11 _Generic expressions

cpp/ql/lib/semmle/code/cpp/PrintAST.qll

@@ -385,6 +385,19 @@ class CastNode extends ConversionNode {
   }
 }
 
+/**
+ * A node representing a `C11GenericExpr`.
+ */
+class C11GenericNode extends ConversionNode {
+  C11GenericExpr generic;
+
+  C11GenericNode() { generic = conv }
+
+  override AstNode getChildInternal(int childIndex) {
+    result.getAst() = generic.getChild(childIndex)
+  }
+}
+
 /**
  * A node representing a `StmtExpr`.
  */

cpp/ql/lib/semmle/code/cpp/exprs/Cast.qll

@@ -831,6 +831,15 @@ class TemporaryObjectExpr extends Conversion, @temp_init {
   override string getAPrimaryQlClass() { result = "TemporaryObjectExpr" }
 }
 
+/**
+ * A node representing a C11 `_Generic` expression.
+ */
+class C11GenericExpr extends Conversion, @c11_generic {
+  override string toString() { result = "_Generic" }
+
+  override string getAPrimaryQlClass() { result = "C11GenericExpr" }
+}
+
 /**
  * A node representing the Cast sub-class of entity `cast`.
  */

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedElement.qll

@@ -128,6 +128,9 @@ private predicate ignoreExprAndDescendants(Expr expr) {
     vaStartExpr.getLastNamedParameter().getFullyConverted() = expr
   )
   or
+  // The children of C11 _Generic expressions are just surface syntax.
+  exists(C11GenericExpr generic | generic.getAChild() = expr)
+  or
   // Do not translate implicit destructor calls for unnamed temporary variables that are
   // conditionally constructed (until we have a mechanism for calling these only when the
   // temporary's constructor was run)
@@ -432,6 +435,9 @@ predicate ignoreLoad(Expr expr) {
     // The load is duplicated from the right operand.
     isExtractorFrontendVersion65OrHigher() and expr instanceof CommaExpr
     or
+    // The load is duplicated from the chosen expression.
+    expr instanceof C11GenericExpr
+    or
     expr.(PointerDereferenceExpr).getOperand().getFullyConverted().getType().getUnspecifiedType()
       instanceof FunctionPointerType
     or

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedExpr.qll

@@ -893,7 +893,8 @@ class TranslatedTransparentConversion extends TranslatedTransparentExpr {
     (
       expr instanceof ParenthesisExpr or
       expr instanceof ReferenceDereferenceExpr or
-      expr instanceof ReferenceToExpr
+      expr instanceof ReferenceToExpr or
+      expr instanceof C11GenericExpr
     )
   }
 

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -1210,6 +1210,7 @@ conversionkinds(
             | @reference_to
             | @ref_indirect
             | @temp_init
+            | @c11_generic
             ;
 
 /*
@@ -1788,6 +1789,7 @@ case @expr.kind of
 | 382 = @isvalidwinrttype
 | 383 = @iswinclass
 | 384 = @iswininterface
+| 385 = @c11_generic
 ;
 
 @var_args_expr = @vastartexpr

cpp/ql/test/library-tests/c11_generic/PrintAST.qlref

@@ -0,0 +1 @@
+semmle/code/cpp/PrintAST.ql

cpp/ql/test/library-tests/c11_generic/macro_invocation.expected

@@ -0,0 +1,8 @@
+| generic.c:21:22:21:32 | _Generic | generic.c:21:22:21:32 | describe(val) |
+| generic.c:22:22:22:32 | _Generic | generic.c:22:22:22:32 | describe(val) |
+| generic.c:23:22:23:32 | _Generic | generic.c:23:22:23:32 | describe(val) |
+| generic.c:24:22:24:32 | _Generic | generic.c:24:22:24:32 | describe(val) |
+| generic.cpp:22:22:22:32 | _Generic | generic.cpp:22:22:22:32 | describe(val) |
+| generic.cpp:23:22:23:32 | _Generic | generic.cpp:23:22:23:32 | describe(val) |
+| generic.cpp:24:22:24:32 | _Generic | generic.cpp:24:22:24:32 | describe(val) |
+| generic.cpp:25:22:25:32 | _Generic | generic.cpp:25:22:25:32 | describe(val) |

cpp/ql/test/library-tests/c11_generic/macro_invocation.ql

@@ -0,0 +1,5 @@
+import cpp
+
+from C11GenericExpr g, MacroInvocation m
+where m.getAnExpandedElement() = g
+select g, m

cpp/ql/test/library-tests/ir/ir/PrintAST.expected

@@ -4180,7 +4180,7 @@ destructors_for_temps.cpp:
 #  103|             ValueCategory = prvalue
 #  104|     getStmt(1): [ReturnStmt] return ...
 generic.c:
-#    7| [TopLevelFunction] char const* c11_generic()
+#    7| [TopLevelFunction] char const* c11_generic_1()
 #    7|   <params>: 
 #    8|   getEntryPoint(): [BlockStmt] { ... }
 #    9|     getStmt(0): [DeclStmt] declaration
@@ -4198,6 +4198,104 @@ generic.c:
 #   11|         getExpr(): [ArrayToPointerConversion] array to pointer conversion
 #   11|             Type = [CharPointerType] char *
 #   11|             ValueCategory = prvalue
+#   11|           getExpr(): [C11GenericExpr] _Generic
+#   11|               Type = [ArrayType] char[4]
+#   11|               ValueCategory = lvalue
+#   11|             getChild(0): [VariableAccess] i
+#   11|                 Type = [IntType] int
+#   11|                 ValueCategory = prvalue(load)
+#   11|             getChild(1): [TypeName] int
+#   11|                 Type = [IntType] int
+#   11|                 ValueCategory = prvalue
+#   11|             getChild(2): [ReuseExpr] reuse of int
+#   11|                 Type = [ArrayType] char[4]
+#   11|                 ValueCategory = lvalue
+#   11|             getChild(3): [TypeName] void
+#   11|                 Type = [VoidType] void
+#   11|                 ValueCategory = prvalue
+#   11|             getChild(4): unknown
+#   11|                 Type = [ArrayType] char[8]
+#   11|                 Value = [StringLiteral] "unknown"
+#   11|                 ValueCategory = lvalue
+#   11|             getChild(0).getFullyConverted(): [ParenthesisExpr] (...)
+#   11|                 Type = [IntType] int
+#   11|                 ValueCategory = prvalue(load)
+#   14| [TopLevelFunction] void enk_c11_generic_2(unsigned int, int)
+#   14|   <params>: 
+#   14|     getParameter(0): [Parameter] x
+#   14|         Type = [IntType] unsigned int
+#   14|     getParameter(1): [Parameter] y
+#   14|         Type = [IntType] int
+#   14|   getEntryPoint(): [BlockStmt] { ... }
+#   15|     getStmt(0): [DeclStmt] declaration
+#   15|       getDeclarationEntry(0): [VariableDeclarationEntry] definition of r
+#   15|           Type = [IntType] unsigned int
+#   16|     getStmt(1): [ExprStmt] ExprStmt
+#   16|       getExpr(): [AssignExpr] ... = ...
+#   16|           Type = [IntType] unsigned int
+#   16|           ValueCategory = prvalue
+#   16|         getLValue(): [VariableAccess] r
+#   16|             Type = [IntType] unsigned int
+#   16|             ValueCategory = lvalue
+#   16|         getRValue(): [AddExpr] ... + ...
+#   16|             Type = [IntType] unsigned int
+#   16|             ValueCategory = prvalue
+#   16|           getLeftOperand(): [VariableAccess] x
+#   16|               Type = [IntType] unsigned int
+#   16|               ValueCategory = lvalue
+#   16|           getRightOperand(): [Literal] 1
+#   16|               Type = [IntType] int
+#   16|               Value = [Literal] 1
+#   16|               ValueCategory = prvalue
+#   16|           getLeftOperand().getFullyConverted(): [C11GenericExpr] _Generic
+#   16|               Type = [IntType] unsigned int
+#   16|               ValueCategory = prvalue
+#   16|             getChild(0): [VariableAccess] r
+#   16|                 Type = [IntType] unsigned int
+#   16|                 ValueCategory = prvalue(load)
+#   16|             getChild(1): [TypeName] unsigned int
+#   16|                 Type = [IntType] unsigned int
+#   16|                 ValueCategory = prvalue
+#   16|             getChild(2): [ReuseExpr] reuse of x
+#   16|                 Type = [IntType] unsigned int
+#   16|                 ValueCategory = lvalue
+#   16|             getChild(3): [TypeName] int
+#   16|                 Type = [IntType] int
+#   16|                 ValueCategory = prvalue
+#   16|             getChild(4): [VariableAccess] y
+#   16|                 Type = [IntType] int
+#   16|                 ValueCategory = lvalue
+#   16|           getRightOperand().getFullyConverted(): [CStyleCast] (unsigned int)...
+#   16|               Conversion = [IntegralConversion] integral conversion
+#   16|               Type = [IntType] unsigned int
+#   16|               Value = [CStyleCast] 1
+#   16|               ValueCategory = prvalue
+#   18|     getStmt(2): [DeclStmt] declaration
+#   18|       getDeclarationEntry(0): [VariableDeclarationEntry] definition of s
+#   18|           Type = [IntType] unsigned int
+#   19|     getStmt(3): [ExprStmt] ExprStmt
+#   19|       getExpr(): [AssignExpr] ... = ...
+#   19|           Type = [IntType] unsigned int
+#   19|           ValueCategory = prvalue
+#   19|         getLValue(): [VariableAccess] s
+#   19|             Type = [IntType] unsigned int
+#   19|             ValueCategory = lvalue
+#   19|         getRValue(): [AddExpr] ... + ...
+#   19|             Type = [IntType] unsigned int
+#   19|             ValueCategory = prvalue
+#   19|           getLeftOperand(): [VariableAccess] x
+#   19|               Type = [IntType] unsigned int
+#   19|               ValueCategory = prvalue(load)
+#   19|           getRightOperand(): [Literal] 1
+#   19|               Type = [IntType] int
+#   19|               Value = [Literal] 1
+#   19|               ValueCategory = prvalue
+#   19|           getRightOperand().getFullyConverted(): [CStyleCast] (unsigned int)...
+#   19|               Conversion = [IntegralConversion] integral conversion
+#   19|               Type = [IntType] unsigned int
+#   19|               Value = [CStyleCast] 1
+#   19|               ValueCategory = prvalue
+#   20|     getStmt(4): [ReturnStmt] return ...
 ir.c:
 #    5| [TopLevelFunction] int getX(MyCoords*)
 #    5|   <params>: 

cpp/ql/test/library-tests/ir/ir/aliased_ir.expected

@@ -2959,7 +2959,7 @@ destructors_for_temps.cpp:
 #  102|     v102_10(void)                        = ExitFunction                             : 
 
 generic.c:
-#    7| char const* c11_generic()
+#    7| char const* c11_generic_1()
 #    7|   Block 0
 #    7|     v7_1(void)            = EnterFunction            : 
 #    7|     m7_2(unknown)         = AliasedDefinition        : 
@@ -2977,6 +2977,37 @@ generic.c:
 #    7|     v7_7(void)            = AliasedUse               : m7_3
 #    7|     v7_8(void)            = ExitFunction             : 
 
+#   14| void enk_c11_generic_2(unsigned int, int)
+#   14|   Block 0
+#   14|     v14_1(void)                = EnterFunction          : 
+#   14|     m14_2(unknown)             = AliasedDefinition      : 
+#   14|     m14_3(unknown)             = InitializeNonLocal     : 
+#   14|     m14_4(unknown)             = Chi                    : total:m14_2, partial:m14_3
+#   14|     r14_5(glval<unsigned int>) = VariableAddress[x]     : 
+#   14|     m14_6(unsigned int)        = InitializeParameter[x] : &:r14_5
+#   14|     m14_7(unknown)             = Chi                    : total:m14_4, partial:m14_6
+#   14|     r14_8(glval<int>)          = VariableAddress[y]     : 
+#   14|     m14_9(int)                 = InitializeParameter[y] : &:r14_8
+#   15|     r15_1(glval<unsigned int>) = VariableAddress[r]     : 
+#   15|     m15_2(unsigned int)        = Uninitialized[r]       : &:r15_1
+#   16|     r16_1(glval<unsigned int>) = VariableAddress[x]     : 
+#   16|     r16_2(unsigned int)        = Constant[1]            : 
+#   16|     r16_3(unsigned int)        = Add                    : r16_1, r16_2
+#   16|     r16_4(glval<unsigned int>) = VariableAddress[r]     : 
+#   16|     m16_5(unsigned int)        = Store[r]               : &:r16_4, r16_3
+#   18|     r18_1(glval<unsigned int>) = VariableAddress[s]     : 
+#   18|     m18_2(unsigned int)        = Uninitialized[s]       : &:r18_1
+#   19|     r19_1(glval<unsigned int>) = VariableAddress[x]     : 
+#   19|     r19_2(unsigned int)        = Load[x]                : &:r19_1, m14_6
+#   19|     r19_3(unsigned int)        = Constant[1]            : 
+#   19|     r19_4(unsigned int)        = Add                    : r19_2, r19_3
+#   19|     r19_5(glval<unsigned int>) = VariableAddress[s]     : 
+#   19|     m19_6(unsigned int)        = Store[s]               : &:r19_5, r19_4
+#   20|     v20_1(void)                = NoOp                   : 
+#   14|     v14_10(void)               = ReturnVoid             : 
+#   14|     v14_11(void)               = AliasedUse             : m14_3
+#   14|     v14_12(void)               = ExitFunction           : 
+
 ir.c:
 #    7| void MyCoordsTest(int)
 #    7|   Block 0

cpp/ql/test/library-tests/ir/ir/generic.c

@@ -4,11 +4,19 @@
     default: "unknown" \
   )
 
-const char *c11_generic()
+const char *c11_generic_1()
 {
   int i;
 
   return describe(i);
 }
 
-// semmle-extractor-options: -std=c11
+void enk_c11_generic_2(unsigned int x, int y) {
+  unsigned int r;
+  r = _Generic(r, unsigned int: x, int: y) + 1;
+
+  unsigned int s;
+  s = x + 1;
+}
+
+// semmle-extractor-options: -std=c11

cpp/ql/test/library-tests/ir/ir/raw_ir.expected

@@ -2733,7 +2733,7 @@ destructors_for_temps.cpp:
 #  102|     v102_8(void)                         = ExitFunction                             : 
 
 generic.c:
-#    7| char const* c11_generic()
+#    7| char const* c11_generic_1()
 #    7|   Block 0
 #    7|     v7_1(void)            = EnterFunction            : 
 #    7|     mu7_2(unknown)        = AliasedDefinition        : 
@@ -2750,6 +2750,35 @@ generic.c:
 #    7|     v7_6(void)            = AliasedUse               : ~m?
 #    7|     v7_7(void)            = ExitFunction             : 
 
+#   14| void enk_c11_generic_2(unsigned int, int)
+#   14|   Block 0
+#   14|     v14_1(void)                = EnterFunction          : 
+#   14|     mu14_2(unknown)            = AliasedDefinition      : 
+#   14|     mu14_3(unknown)            = InitializeNonLocal     : 
+#   14|     r14_4(glval<unsigned int>) = VariableAddress[x]     : 
+#   14|     mu14_5(unsigned int)       = InitializeParameter[x] : &:r14_4
+#   14|     r14_6(glval<int>)          = VariableAddress[y]     : 
+#   14|     mu14_7(int)                = InitializeParameter[y] : &:r14_6
+#   15|     r15_1(glval<unsigned int>) = VariableAddress[r]     : 
+#   15|     mu15_2(unsigned int)       = Uninitialized[r]       : &:r15_1
+#   16|     r16_1(glval<unsigned int>) = VariableAddress[x]     : 
+#   16|     r16_2(unsigned int)        = Constant[1]            : 
+#   16|     r16_3(unsigned int)        = Add                    : r16_1, r16_2
+#   16|     r16_4(glval<unsigned int>) = VariableAddress[r]     : 
+#   16|     mu16_5(unsigned int)       = Store[r]               : &:r16_4, r16_3
+#   18|     r18_1(glval<unsigned int>) = VariableAddress[s]     : 
+#   18|     mu18_2(unsigned int)       = Uninitialized[s]       : &:r18_1
+#   19|     r19_1(glval<unsigned int>) = VariableAddress[x]     : 
+#   19|     r19_2(unsigned int)        = Load[x]                : &:r19_1, ~m?
+#   19|     r19_3(unsigned int)        = Constant[1]            : 
+#   19|     r19_4(unsigned int)        = Add                    : r19_2, r19_3
+#   19|     r19_5(glval<unsigned int>) = VariableAddress[s]     : 
+#   19|     mu19_6(unsigned int)       = Store[s]               : &:r19_5, r19_4
+#   20|     v20_1(void)                = NoOp                   : 
+#   14|     v14_8(void)                = ReturnVoid             : 
+#   14|     v14_9(void)                = AliasedUse             : ~m?
+#   14|     v14_10(void)               = ExitFunction           : 
+
 ir.c:
 #    7| void MyCoordsTest(int)
 #    7|   Block 0