[clang] [llvm] [BPF] introduce `__attribute__((bpf_fastcall))` (PR #101228)

[via llvm-commits]

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@@ -596,6 +600,90 @@ bool BPFMIPreEmitPeephole::adjustBranch() {
   return Changed;
 }
 
+static const unsigned CallerSavedRegs[] = {BPF::R0, BPF::R1, BPF::R2,
+                                           BPF::R3, BPF::R4, BPF::R5};
+
+struct BPFFastCall {
+  MachineInstr *MI;
+  unsigned LiveCallerSavedRegs;
+};
+
+static void collectBPFFastCalls(const TargetRegisterInfo *TRI,
+                                LivePhysRegs &LiveRegs, MachineBasicBlock &BB,
+                                SmallVectorImpl<BPFFastCall> &Calls) {
+  LiveRegs.init(*TRI);
+  LiveRegs.addLiveOuts(BB);
+  Calls.clear();
+  for (MachineInstr &MI : llvm::reverse(BB)) {
+    unsigned LiveCallerSavedRegs;
+    if (!MI.isCall())
+      goto NextInsn;
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yonghong-song wrote:

I am not 100% sure. But let us try to avoid 'goto' statement?

https://github.com/llvm/llvm-project/pull/101228