[llvm] [RISCV][VLOPT] Allow propagation even when VL isn't VLMAX (PR #112228)

[Michael Maitland via llvm-commits]

================
@@ -713,16 +736,15 @@ bool RISCVVLOptimizer::checkUsers(std::optional<Register> &CommonVL,
 
     unsigned VLOpNum = RISCVII::getVLOpNum(Desc);
     const MachineOperand &VLOp = UserMI.getOperand(VLOpNum);
-    // Looking for a register VL that isn't X0.
-    if (!VLOp.isReg() || VLOp.getReg() == RISCV::X0) {
-      LLVM_DEBUG(dbgs() << "    Abort due to user uses X0 as VL.\n");
-      CanReduceVL = false;
-      break;
-    }
+
+    // Looking for an immediate or a register VL that isn't X0.
+    assert(!VLOp.isReg() ||
+           VLOp.getReg() != RISCV::X0 && "Did not expect X0 VL");
 
     if (!CommonVL) {
-      CommonVL = VLOp.getReg();
-    } else if (*CommonVL != VLOp.getReg()) {
+      CommonVL = &VLOp;
+      LLVM_DEBUG(dbgs() << "    User VL is: " << VLOp << "\n");
+    } else if (!CommonVL->isIdenticalTo(VLOp)) {
----------------
michaelmaitland wrote:

Agreed.

https://github.com/llvm/llvm-project/pull/112228