[llvm] [RISCV] Move vmv.v.v peephole from SelectionDAG to RISCVVectorPeephole (PR #100367)

[Philip Reames via llvm-commits]

================
@@ -297,6 +298,143 @@ bool RISCVVectorPeephole::convertToUnmasked(MachineInstr &MI) const {
   return true;
 }
 
+/// Given two VL operands, returns the one known to be the smallest or nullptr
+/// if unknown.
+static const MachineOperand *getKnownMinVL(const MachineOperand *LHS,
+                                           const MachineOperand *RHS) {
+  if (LHS->isReg() && RHS->isReg() && LHS->getReg().isVirtual() &&
+      LHS->getReg() == RHS->getReg())
+    return LHS;
+  if (LHS->isImm() && LHS->getImm() == RISCV::VLMaxSentinel)
+    return RHS;
+  if (RHS->isImm() && RHS->getImm() == RISCV::VLMaxSentinel)
+    return LHS;
+  if (!LHS->isImm() || !RHS->isImm())
+    return nullptr;
+  return LHS->getImm() <= RHS->getImm() ? LHS : RHS;
+}
+
+/// Check if it's safe to move From down to To, checking that no physical
+/// registers are clobbered.
+static bool isSafeToMove(const MachineInstr &From, const MachineInstr &To) {
+  assert(From.getParent() == To.getParent() && !From.hasImplicitDef());
+  SmallVector<Register> PhysUses;
+  for (const MachineOperand &MO : From.all_uses())
+    if (MO.getReg().isPhysical())
+      PhysUses.push_back(MO.getReg());
+  bool SawStore = false;
+  for (auto II = From.getIterator(); II != To.getIterator(); II++) {
+    for (Register PhysReg : PhysUses)
+      if (II->definesRegister(PhysReg, nullptr))
+        return false;
+    if (II->mayStore()) {
+      SawStore = true;
+      break;
+    }
+  }
+  return From.isSafeToMove(nullptr, SawStore);
+}
+
+static const RISCV::RISCVMaskedPseudoInfo *
+lookupMaskedPseudoInfo(const MachineInstr &MI) {
+  const RISCV::RISCVMaskedPseudoInfo *Info =
+      RISCV::lookupMaskedIntrinsicByUnmasked(MI.getOpcode());
+  if (!Info)
+    Info = RISCV::getMaskedPseudoInfo(MI.getOpcode());
+  return Info;
+}
+
+/// If a PseudoVMV_V_V is the only user of it's input, fold its passthru and VL
+/// into it.
+///
+/// %x = PseudoVADD_V_V_M1 %passthru, %a, %b, %vl, sew, policy
----------------
preames wrote:

The comment should use vl1 and vl2, and a min(vl1, vl2) in the result for clarity.

https://github.com/llvm/llvm-project/pull/100367