[llvm] [RISCV] Don't lose elements from False in vmerge -> vmv peephole (PR #149720)

[Craig Topper via llvm-commits]

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@@ -434,6 +434,14 @@ bool RISCVVectorPeephole::convertSameMaskVMergeToVMv(MachineInstr &MI) {
   if (!isKnownSameDefs(TrueMask.getReg(), MIMask.getReg()))
     return false;
 
+  // Masked off lanes past TrueVL will come from False, and converting to vmv
+  // will lose these lanes unless MIVL <= TrueVL.
+  MachineOperand &MIVL = MI.getOperand(RISCVII::getVLOpNum(MI.getDesc()));
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topperc wrote:

Should these be const references?

https://github.com/llvm/llvm-project/pull/149720