[llvm] [AMDGPU] Compiler should synthesize private buffer resource descriptor from flat_scratch_init (PR #79586)

[Matt Arsenault via llvm-commits]

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@@ -610,11 +612,15 @@ void SIFrameLowering::emitEntryFunctionPrologue(MachineFunction &MF,
   const SIInstrInfo *TII = ST.getInstrInfo();
   const SIRegisterInfo *TRI = &TII->getRegisterInfo();
   MachineRegisterInfo &MRI = MF.getRegInfo();
-  const Function &F = MF.getFunction();
   MachineFrameInfo &FrameInfo = MF.getFrameInfo();
 
   assert(MFI->isEntryFunction());
 
+  bool NeedsFlatScratchInit =
+      MFI->getUserSGPRInfo().hasFlatScratchInit() &&
+      (MRI.isPhysRegUsed(AMDGPU::FLAT_SCR) || FrameInfo.hasCalls() ||
+       (!allStackObjectsAreDead(FrameInfo) && ST.enableFlatScratch()));
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arsenm wrote:

We could avoid some of this if we fixed #63586

https://github.com/llvm/llvm-project/pull/79586