[SYCL] Allow __failed_assertion to support libstdc++-11

clang/lib/Sema/SemaSYCL.cpp

@@ -61,6 +61,8 @@ static constexpr llvm::StringLiteral InitESIMDMethodName = "__init_esimd";
 static constexpr llvm::StringLiteral InitSpecConstantsBuffer =
     "__init_specialization_constants_buffer";
 static constexpr llvm::StringLiteral FinalizeMethodName = "__finalize";
+static constexpr llvm::StringLiteral LibstdcxxFailedAssertion =
+    "__failed_assertion";
 constexpr unsigned MaxKernelArgsSize = 2048;
 
 namespace {
@@ -320,6 +322,21 @@ static bool isSYCLKernelBodyFunction(FunctionDecl *FD) {
   return FD->getOverloadedOperator() == OO_Call;
 }
 
+static bool isSYCLUndefinedAllowed(const FunctionDecl *Callee,
+                                   const SourceManager &SrcMgr) {
+  if (!Callee)
+    return false;
+
+  // libstdc++-11 introduced an undefined function "void __failed_assertion()"
+  // which may lead to SemaSYCL check failure. However, this undefined function
+  // is used to trigger some compilation error when the check fails at compile
+  // time and will be ignored when the check succeeds. We allow calls to this
+  // function to support some important std functions in SYCL device.
+  return (Callee->getName() == LibstdcxxFailedAssertion) &&
+         Callee->getNumParams() == 0 && Callee->getReturnType()->isVoidType() &&
+         SrcMgr.isInSystemHeader(Callee->getLocation());
+}
+
 // Helper function to report conflicting function attributes.
 // F - the function, A1 - function attribute, A2 - the attribute it conflicts
 // with.
@@ -4122,7 +4139,10 @@ void Sema::finalizeSYCLDelayedAnalysis(const FunctionDecl *Caller,
     return;
 
   // Diagnose if this is an undefined function and it is not a builtin.
-  if (!Callee->isDefined() && !Callee->getBuiltinID()) {
+  // Currently, there is an exception of "__failed_assertion" in libstdc++-11,
+  // this undefined function is used to trigger a compiling error.
+  if (!Callee->isDefined() && !Callee->getBuiltinID() &&
+      !isSYCLUndefinedAllowed(Callee, getSourceManager())) {
     Diag(Loc, diag::err_sycl_restrict) << Sema::KernelCallUndefinedFunction;
     Diag(Callee->getLocation(), diag::note_previous_decl) << Callee;
     Diag(Caller->getLocation(), diag::note_called_by) << Caller;

clang/test/SemaSYCL/Inputs/dummy_failed_assert

@@ -0,0 +1 @@
+void __failed_assertion();

clang/test/SemaSYCL/__failed_assertion.cpp

@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -fsycl-is-device -internal-isystem %S/Inputs -sycl-std=2020 -verify -DUSR -fsyntax-only %s
+// RUN: %clang_cc1 -fsycl-is-device -internal-isystem %S/Inputs -sycl-std=2020 -verify -fsyntax-only %s
+// UNSUPPORTED: system-windows
+// This test checks that an undefined "__failed_assertion" without SYCL_EXTERNAL will lead to SYCL sema check
+// failure if it is not declared in a system header otherwise no SYCL sema check failure will be triggered.
+
+#include "sycl.hpp"
+#ifdef USR
+void __failed_assertion();
+// expected-note@-1 {{'__failed_assertion' declared here}}
+#else
+#include <dummy_failed_assert>
+#endif
+
+#ifdef USR
+SYCL_EXTERNAL
+void call_failed_assertion() {
+  // expected-note@-1 {{called by 'call_failed_assertion'}}
+  __failed_assertion();
+  // expected-error@-1 {{SYCL kernel cannot call an undefined function without SYCL_EXTERNAL attribute}}
+}
+#else
+// expected-no-diagnostics
+SYCL_EXTERNAL
+void call_failed_assertion() {
+  __failed_assertion();
+}
+#endif
+