[llvm] [MachineLICM] Let targets decide if copy-like instructions are cheap (PR #146599)

[Guy David via llvm-commits]

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@@ -1219,7 +1219,7 @@ bool MachineLICMImpl::HasHighOperandLatency(MachineInstr &MI, unsigned DefIdx,
 /// Return true if the instruction is marked "cheap" or the operand latency
 /// between its def and a use is one or less.
 bool MachineLICMImpl::IsCheapInstruction(MachineInstr &MI) const {
-  if (TII->isAsCheapAsAMove(MI) || MI.isCopyLike())
+  if (TII->isAsCheapAsAMove(MI))
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guy-david wrote:

Maybe the hoisting of a `SUBREG_TO_REG` permitted the hoisting of other instructions, eventually leading to more optimized code? Just like the test case here. 

https://github.com/llvm/llvm-project/pull/146599