[SYCL] Fix int-footer spec-const generation for deduced types. (#3908)

Apparently my initial implementation documented the need to do this, but
never did!  We collect SpecConstants (the vector), and add ones we don't
know if they are SpecConstants. However, the previous implementation
forgot to skip the VarDecls that were later deduced to be a different
type.

Author: Erich Keane

clang/lib/Sema/SemaSYCL.cpp

@@ -4852,7 +4852,6 @@ void SYCLIntegrationFooter::addVarDecl(const VarDecl *VD) {
     // rest of this file, is called during Sema instead of after it. We will
     // also have to filter out after deduction later.
     QualType Ty = VD->getType().getCanonicalType();
-
     if (!Ty->isUndeducedType())
       return;
   }
@@ -5024,11 +5023,24 @@ bool SYCLIntegrationFooter::emit(raw_ostream &OS) {
   Policy.SuppressTypedefs = true;
   Policy.SuppressUnwrittenScope = true;
 
+  llvm::SmallSet<const VarDecl *, 8> VisitedSpecConstants;
+
   // Used to uniquely name the 'shim's as we generate the names in each
   // anonymous namespace.
   unsigned ShimCounter = 0;
   for (const VarDecl *VD : SpecConstants) {
     VD = VD->getCanonicalDecl();
+
+    // Skip if this isn't a SpecIdType.  This can happen if it was a deduced
+    // type.
+    if (!Util::isSyclSpecIdType(VD->getType()))
+      continue;
+
+    // Skip if we've already visited this.
+    if (llvm::find(VisitedSpecConstants, VD) != VisitedSpecConstants.end())
+      continue;
+
+    VisitedSpecConstants.insert(VD);
     std::string TopShim = EmitSpecIdShims(OS, ShimCounter, VD);
     OS << "__SYCL_INLINE_NAMESPACE(cl) {\n";
     OS << "namespace sycl {\n";

clang/test/CodeGenSYCL/integration_footer.cpp

@@ -144,4 +144,19 @@ specialization_id<int> AnonNSSpecID;
 
 } // namespace Foo
 
+// make sure we don't emit a deduced type that isn't a spec constant.
+enum SomeEnum { SE_A };
+enum AnotherEnum : unsigned int { AE_A };
+
+template<SomeEnum E> struct GetThing{};
+template<> struct GetThing<SE_A>{
+  static constexpr auto thing = AE_A;
+};
+
+struct container {
+  static constexpr auto Thing = GetThing<SE_A>::thing;
+};
+// CHECK-NOT: ::GetThing
+// CHECK-NOT: ::container::Thing
+
 // CHECK: #include <CL/sycl/detail/spec_const_integration.hpp>