[llvm] [RISCV][TTI] Scale the cost of the sext/zext with LMUL (PR #86617)

[Luke Lau via llvm-commits]

================
@@ -915,15 +916,21 @@ InstructionCost RISCVTTIImpl::getCastInstrCost(unsigned Opcode, Type *Dst,
                   (int)Log2_32(Src->getScalarSizeInBits());
     switch (ISD) {
     case ISD::SIGN_EXTEND:
-    case ISD::ZERO_EXTEND:
-      if (Src->getScalarSizeInBits() == 1) {
-        // We do not use vsext/vzext to extend from mask vector.
-        // Instead we use the following instructions to extend from mask vector:
-        // vmv.v.i v8, 0
-        // vmerge.vim v8, v8, -1, v0
----------------
lukel97 wrote:

Can we keep the comment?

https://github.com/llvm/llvm-project/pull/86617