[llvm] Spill/restore FP/BP around instructions in which they are clobbered (PR #81048)

[Reid Kleckner via llvm-commits]

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@@ -228,6 +228,8 @@ bool PEI::runOnMachineFunction(MachineFunction &MF) {
   FrameIndexVirtualScavenging = TRI->requiresFrameIndexScavenging(MF);
   ORE = &getAnalysis<MachineOptimizationRemarkEmitterPass>().getORE();
 
+  TFI->spillFPBP(MF);
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rnk wrote:

The PEI process is very complicated, please add comments elaborating on what this does and why it comes before call frame instruction elimination.

https://github.com/llvm/llvm-project/pull/81048