[clang] [SYCL] SYCL host kernel launch support for the sycl_kernel_entry_point attribute. (PR #152403)

[Tom Honermann via cfe-commits]

================
@@ -16227,6 +16227,32 @@ Decl *Sema::ActOnStartOfFunctionDef(Scope *FnBodyScope, Decl *D,
 
   maybeAddDeclWithEffects(FD);
 
+  if (FD && !FD->isInvalidDecl() && FD->hasAttr<SYCLKernelEntryPointAttr>() &&
+      FnBodyScope) {
+    // An implicit call expression is synthesized for functions declared with
+    // the sycl_kernel_entry_point attribute. The call may resolve to a
+    // function template, a member function template, or a call operator
+    // of a variable template depending on the results of unqualified lookup
+    // for 'sycl_kernel_launch' from the beginning of the function body.
+    // Performing that lookup requires the stack of parsing scopes active
+    // when the definition is parsed and is thus done here; the result is
+    // cached in FunctionScopeInfo and used to synthesize the (possibly
+    // unresolved) call expression after the function body has been parsed.
+    const auto *SKEPAttr = FD->getAttr<SYCLKernelEntryPointAttr>();
+    if (!SKEPAttr->isInvalidAttr()) {
+      ExprResult LaunchIdExpr =
+          SYCL().BuildSYCLKernelLaunchIdExpr(FD, SKEPAttr->getKernelName());
+      if (LaunchIdExpr.isInvalid()) {
+        // Do not mark 'FD' as invalid. Name lookup failure for
+        // 'sycl_kernel_launch' is treated as an error in the definition of
+        // 'FD'; treating it as an error of the declaration would affect
+        // overload resolution.
+      }
----------------
tahonermann wrote:

I agree it is a bit odd. I wrote it this way because the absence of a check would be somewhat suspicious, so I wanted to clearly communicate that it has been considered and handled (by not doing anything about it here). I haven't manged to find a comment-only change that I'm fond of. Is this an improvement?
```suggestion
      // Do not mark 'FD' as invalid if construction of `LaunchIDExpr` produces
      // an invalid result. Name lookup failure for 'sycl_kernel_launch' is
      // treated as an error in the definition of 'FD'; treating it as an error
      // of the declaration would affect overload resolution.
```

https://github.com/llvm/llvm-project/pull/152403