[clang] handle extended integer constant expressions in _Static_assert (PR #57687)

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D134311

clang/docs/ReleaseNotes.rst

@@ -99,6 +99,9 @@ Major New Features
 
 Bug Fixes
 ---------
+- Correct ``_Static_assert`` to accept the same set of extended integer
+  constant expressions as is accpted in other contexts that accept them.
+  This fixes `Issue 57687 <https://github.com/llvm/llvm-project/issues/57687>`_.
 - Fixes an accepts-invalid bug in C when using a ``_Noreturn`` function
   specifier on something other than a function declaration. This fixes
   `Issue 56800 <https://github.com/llvm/llvm-project/issues/56800>`_.

clang/lib/Sema/SemaDeclCXX.cpp

@@ -16736,10 +16736,21 @@ Decl *Sema::BuildStaticAssertDeclaration(SourceLocation StaticAssertLoc,
       AssertExpr = FullAssertExpr.get();
 
     llvm::APSInt Cond;
+    Expr *BaseExpr = AssertExpr;
+    AllowFoldKind FoldKind = NoFold;
+
+    if (!getLangOpts().CPlusPlus) {
+      // In C mode only allow folding and strip the implicit conversion
+      // to the type of the first _Static_assert argument that would
+      // otherwise suppress diagnostics for arguments that convert to int.
+      FoldKind = AllowFold;
+      BaseExpr = BaseExpr->IgnoreImpCasts();
+    }
+
     if (!Failed && VerifyIntegerConstantExpression(
-                       AssertExpr, &Cond,
+                       BaseExpr, &Cond,
-                       diag::err_static_assert_expression_is_not_constant)
+                       diag::err_static_assert_expression_is_not_constant,
-                       .isInvalid())
+                       FoldKind).isInvalid())
       Failed = true;
 
     if (!Failed && !Cond) {

clang/test/Sema/static-assert.c

@@ -74,3 +74,23 @@ static_assert(1, "1 is nonzero"); // ms-warning {{use of 'static_assert' without
 
 _Static_assert(1 , "") // expected-error {{expected ';' after '_Static_assert'}} \
                       // ext-warning {{'_Static_assert' is a C11 extension}}
+
+static int static_var;
+_Static_assert(&static_var != 0, "");  // ext-warning {{'_Static_assert' is a C11 extension}} \
+                                       // expected-warning {{comparison of address of 'static_var' not equal to a null pointer is always true}}
+_Static_assert("" != 0, "");           // ext-warning {{'_Static_assert' is a C11 extension}}
+_Static_assert(("" != 0), "");         // ext-warning {{'_Static_assert' is a C11 extension}}
+_Static_assert(*"1", "");              // ext-warning {{'_Static_assert' is a C11 extension}}
+_Static_assert("1"[0], "");            // ext-warning {{'_Static_assert' is a C11 extension}}
+_Static_assert(1.0 != 0, "");          // ext-warning {{'_Static_assert' is a C11 extension}}
+_Static_assert(__builtin_strlen("1"), "");  // ext-warning {{'_Static_assert' is a C11 extension}}
+#ifndef __cplusplus
+// ext-warning@-9 {{expression is not an integer constant expression; folding it to a constant is a GNU extension}}
+// ext-warning@-8 {{expression is not an integer constant expression; folding it to a constant is a GNU extension}}
+// ext-warning@-8 {{expression is not an integer constant expression; folding it to a constant is a GNU extension}}
+// ext-warning@-8 {{expression is not an integer constant expression; folding it to a constant is a GNU extension}}
+// ext-warning@-8 {{expression is not an integer constant expression; folding it to a constant is a GNU extension}}
+// ext-warning@-8 {{expression is not an integer constant expression; folding it to a constant is a GNU extension}}
+// __builtin_strlen(literal) is considered an integer constant expression
+// and doesn't cause a pedantic warning
+#endif