Create specialization of -Wgnu-statement-expression for expressions found in macros.

-Wgnu-statement-expression currently warns for both direct source uses of statement expressions but also macro expansions; since they may be used by macros to avoid multiple evaluation of macro arguments, engineers might want to suppress warnings when statement expressions are expanded from macros but see them if introduced directly in source code.

Differential Revision: https://reviews.llvm.org/D126522

clang/include/clang/Basic/DiagnosticGroups.td

@@ -611,7 +611,12 @@ def StaticInInline : DiagGroup<"static-in-inline">;
 def StaticLocalInInline : DiagGroup<"static-local-in-inline">;
 def GNUStaticFloatInit : DiagGroup<"gnu-static-float-init">;
 def StaticFloatInit : DiagGroup<"static-float-init", [GNUStaticFloatInit]>;
-def GNUStatementExpression : DiagGroup<"gnu-statement-expression">;
+// Allow differentiation between GNU statement expressions in a macro versus
+// written directly in source.
+def GNUStatementExpressionFromMacroExpansion :
+  DiagGroup<"gnu-statement-expression-from-macro-expansion">;
+def GNUStatementExpression : DiagGroup<"gnu-statement-expression",
+                                       [GNUStatementExpressionFromMacroExpansion]>;
 def StringConcatation : DiagGroup<"string-concatenation">;
 def StringCompare : DiagGroup<"string-compare">;
 def StringPlusInt : DiagGroup<"string-plus-int">;

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -174,6 +174,9 @@ def err_stmtexpr_file_scope : Error<
   "statement expression not allowed at file scope">;
 def ext_gnu_statement_expr : Extension<
   "use of GNU statement expression extension">, InGroup<GNUStatementExpression>;
+def ext_gnu_statement_expr_macro : Extension<
+  "use of GNU statement expression extension from macro expansion">,
+  InGroup<GNUStatementExpressionFromMacroExpansion>;
 def ext_gnu_conditional_expr : Extension<
   "use of GNU ?: conditional expression extension, omitting middle operand">, InGroup<GNUConditionalOmittedOperand>;
 def ext_gnu_empty_initializer : Extension<

clang/lib/Parse/ParseExpr.cpp

@@ -2870,7 +2870,8 @@ Parser::ParseParenExpression(ParenParseOption &ExprType, bool stopIfCastExpr,
   // None of these cases should fall through with an invalid Result
   // unless they've already reported an error.
   if (ExprType >= CompoundStmt && Tok.is(tok::l_brace)) {
-    Diag(Tok, diag::ext_gnu_statement_expr);
+    Diag(Tok, OpenLoc.isMacroID() ? diag::ext_gnu_statement_expr_macro
+                                  : diag::ext_gnu_statement_expr);
 
     checkCompoundToken(OpenLoc, tok::l_paren, CompoundToken::StmtExprBegin);
 

clang/test/Sema/gnu-flags.c

@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s -DNONE -Wno-gnu
-// RUN: %clang_cc1 -fsyntax-only -verify %s -DALL -Wgnu 
+// RUN: %clang_cc1 -fsyntax-only -verify %s -DALL -Wgnu
 // RUN: %clang_cc1 -fsyntax-only -verify %s -DALL -Wno-gnu \
 // RUN:   -Wgnu-alignof-expression -Wgnu-case-range -Wgnu-complex-integer -Wgnu-conditional-omitted-operand \
 // RUN:   -Wgnu-empty-initializer -Wgnu-label-as-value -Wgnu-statement-expression \
@@ -20,6 +20,7 @@
 // %clang_cc1 -fsyntax-only -verify %s -DEMPTYINIT -Wno-gnu -Wgnu-empty-initializer
 // %clang_cc1 -fsyntax-only -verify %s -DLABELVALUE -Wno-gnu -Wgnu-label-as-value
 // %clang_cc1 -fsyntax-only -verify %s -DSTATEMENTEXP -Wno-gnu -Wgnu-statement-expression
+// %clang_cc1 -fsyntax-only -verify %s -DSTATEMENTEXPMACRO -Wno-gnu -Wgnu-statement-expression-from-macro-expansion
 // %clang_cc1 -fsyntax-only -verify %s -DCOMPOUNDLITERALINITIALIZER -Wno-gnu -Wgnu-compound-literal-initializer
 // %clang_cc1 -fsyntax-only -verify %s -DFLEXIBLEARRAYINITIALIZER -Wno-gnu -Wgnu-flexible-array-initializer
 // %clang_cc1 -fsyntax-only -verify %s -DREDECLAREDENUM -Wno-gnu -Wgnu-redeclared-enum
@@ -95,6 +96,14 @@ void statementexp(void)
 	int a = ({ 1; });
 }
 
+#if ALL || STATEMENTEXP || STATEMENTEXPMACRO
+// expected-warning@+5 {{use of GNU statement expression extension from macro expansion}}
+#endif
+
+#define STMT_EXPR_MACRO(a) ({ (a); })
+void statementexprmacro(void) {
+  int a = STMT_EXPR_MACRO(1);
+}
 
 #if ALL || COMPOUNDLITERALINITIALIZER
 // expected-warning@+4 {{initialization of an array of type 'int[5]' from a compound literal of type 'int[5]' is a GNU extension}}