[llvm] [AMDGPU][SIInsertWaitcnts] drop OldWaitcntInstr only when it is processed (PR #145720)

[Jay Foad via llvm-commits]

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@@ -2474,6 +2474,10 @@ bool SIInsertWaitcnts::insertWaitcntInBlock(MachineFunction &MF,
                                          E = Block.instr_end();
        Iter != E;) {
     MachineInstr &Inst = *Iter;
+    if (Inst.isMetaInstruction()) {
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jayfoad wrote:

Does this mean `generateWaitcntInstBefore` no longer has to worry about meta instruction, or could assert that it does not see them?

https://github.com/llvm/llvm-project/pull/145720