[llvm] [RISCV] Handle non uimm5 VL constants in isVLKnownLE (PR #156639)

[Philip Reames via llvm-commits]

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@@ -4807,9 +4820,11 @@ bool RISCV::isVLKnownLE(const MachineOperand &LHS, const MachineOperand &RHS) {
     return true;
   if (LHS.isImm() && LHS.getImm() == RISCV::VLMaxSentinel)
     return false;
-  if (!LHS.isImm() || !RHS.isImm())
+  std::optional<int64_t> LHSImm = getEffectiveImm(LHS, MRI),
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preames wrote:

Are you sure the new logic works properly with VLMaxSentinel?  In particular, what if you get an ADDI which happens to encode -1?  

I think this is correct, just flagging it for extra consideration.

https://github.com/llvm/llvm-project/pull/156639