[llvm] [RISCV] Convert AVLs with vlenb to VLMAX where possible (PR #97800)

[Pengcheng Wang via llvm-commits]

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@@ -62,6 +69,54 @@ char RISCVFoldMasks::ID = 0;
 
 INITIALIZE_PASS(RISCVFoldMasks, DEBUG_TYPE, "RISC-V Fold Masks", false, false)
 
+// If an AVL is a VLENB that's possibly scaled to be equal to VLMAX, convert it
+// to the VLMAX sentinel value.
+bool RISCVFoldMasks::convertToVLMAX(MachineInstr &MI) const {
+  if (!RISCVII::hasVLOp(MI.getDesc().TSFlags) ||
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wangpc-pp wrote:

Looking up table may be slow, I think it's OK to just check VL/SEW.

https://github.com/llvm/llvm-project/pull/97800