[llvm] [AMDGPU] Fix hidden kernarg preload count inconsistency (PR #116759)

[Matt Arsenault via llvm-commits]

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@@ -520,6 +520,16 @@ bool AMDGPUCallLowering::lowerFormalArgumentsKernel(
 
   // TODO: Align down to dword alignment and extract bits for extending loads.
   for (auto &Arg : F.args()) {
+    // Hidden arguments that are in the kernel signature must be preloaded to
+    // user SGPRs, or loaded via the implicit_arg ptr. Print a diagnostic error
+    // if a hidden argument is in the argument list and is not preloaded.
+    if (Arg.hasAttribute("amdgpu-hidden-argument")) {
+      DiagnosticInfoUnsupported NonPreloadHiddenArg(
+          *Arg.getParent(),
+          "hidden argument in kernel signature was not preloaded");
+      F.getContext().diagnose(NonPreloadHiddenArg);
+    }
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arsenm wrote:

I would expect globalisel to be at feature parity, and hit the fallback for unsupported features, not hard error

https://github.com/llvm/llvm-project/pull/116759