[clang] [SYCL] Basic code generation for SYCL kernel caller offload entry point functions. (PR #133030)

[Tom Honermann via cfe-commits]

================
@@ -3303,6 +3303,27 @@ void CodeGenModule::EmitDeferred() {
   CurDeclsToEmit.swap(DeferredDeclsToEmit);
 
   for (GlobalDecl &D : CurDeclsToEmit) {
+    // Functions declared with the sycl_kernel_entry_point attribute are
+    // emitted normally during host compilation. During device compilation,
+    // a SYCL kernel caller offload entry point function is generated and
+    // emitted in place of each of these functions.
+    if (const auto *FD = D.getDecl()->getAsFunction()) {
+      if (LangOpts.SYCLIsDevice && FD->hasAttr<SYCLKernelEntryPointAttr>() &&
+          FD->isDefined()) {
+        // Functions with an invalid sycl_kernel_entry_point attribute are
+        // ignored during device compilation.
+        if (!FD->getAttr<SYCLKernelEntryPointAttr>()->isInvalidAttr()) {
+          // Generate and emit the SYCL kernel caller function.
+          EmitSYCLKernelCaller(FD, getContext());
+          // Recurse to emit any symbols directly or indirectly referenced
+          // by the SYCL kernel caller function.
+          EmitDeferred();
----------------
tahonermann wrote:

This is following what is normally done per the following comment near the end of the function:
```
3271 void CodeGenModule::EmitDeferred() {
....
3359     // If we found out that we need to emit more decls, do that recursively.
3360     // This has the advantage that the decls are emitted in a DFS and related
3361     // ones are close together, which is convenient for testing.
3362     if (!DeferredVTables.empty() || !DeferredDeclsToEmit.empty()) {
3363       EmitDeferred();
3364       assert(DeferredVTables.empty() && DeferredDeclsToEmit.empty());
3365     }
3366   }
3367 }
```

https://github.com/llvm/llvm-project/pull/133030