[llvm] Fix SIFixSGPRCopies To Handle Physical Registers (PR #149859)

[Janek van Oirschot via llvm-commits]

================
@@ -256,17 +256,18 @@ AMDGPUResourceUsageAnalysisImpl::analyzeResourceUsage(
 
         const Function *Callee = getCalleeFunction(*CalleeOp);
 
+        auto isSameFunction = [](const MachineFunction &MF, const Function *F) {
+          return F == &MF.getFunction();
+        };
+
         // Avoid crashing on undefined behavior with an illegal call to a
         // kernel. If a callsite's calling convention doesn't match the
         // function's, it's undefined behavior. If the callsite calling
         // convention does match, that would have errored earlier.
-        if (Callee && AMDGPU::isEntryFunctionCC(Callee->getCallingConv()))
+        if (Callee && AMDGPU::isEntryFunctionCC(Callee->getCallingConv()) &&
+            !isSameFunction(MF, Callee))
           report_fatal_error("invalid call to entry function");
----------------
JanekvO wrote:

AFAIU, the `isEntryFunctionCC`-ness of this is the blocker on why it cannot be a callee, regardless of (self-)recursion. Recursion itself is possible (albeit dubious in terms of resource allocation and runtime use, but I digress) so long as it isn't marked as an entry function.

https://github.com/llvm/llvm-project/pull/149859