[RISCV] Generate Xqcilsm LWMI/SWMI load/store multiple instructions (#171079)

This patch adds support for generating the Xqcilsm load/store multiple
instructions as a part of the RISCVLoadStoreOptimizer pass. For now we
only combine two load/store instructions into a load/store multiple.
Support for converting more loads/stores will be added in follow-up
patches. These instructions are only applicable for 32-bit loads/stores
with an alignment of 4-bytes.

Author: svs-quic

llvm/lib/Target/RISCV/RISCVLoadStoreOptimizer.cpp

@@ -70,6 +70,12 @@ struct RISCVLoadStoreOpt : public MachineFunctionPass {
   // Convert load/store pairs to single instructions.
   bool tryConvertToLdStPair(MachineBasicBlock::iterator First,
                             MachineBasicBlock::iterator Second);
+  bool tryConvertToXqcilsmLdStPair(MachineFunction *MF,
+                                   MachineBasicBlock::iterator First,
+                                   MachineBasicBlock::iterator Second);
+  bool tryConvertToMIPSLdStPair(MachineFunction *MF,
+                                MachineBasicBlock::iterator First,
+                                MachineBasicBlock::iterator Second);
 
   // Scan the instructions looking for a load/store that can be combined
   // with the current instruction into a load/store pair.
@@ -114,7 +120,7 @@ bool RISCVLoadStoreOpt::runOnMachineFunction(MachineFunction &Fn) {
   ModifiedRegUnits.init(*TRI);
   UsedRegUnits.init(*TRI);
 
-  if (Subtarget.useMIPSLoadStorePairs()) {
+  if (Subtarget.useMIPSLoadStorePairs() || Subtarget.hasVendorXqcilsm()) {
     for (MachineBasicBlock &MBB : Fn) {
       LLVM_DEBUG(dbgs() << "MBB: " << MBB.getName() << "\n");
 
@@ -168,14 +174,93 @@ bool RISCVLoadStoreOpt::tryToPairLdStInst(MachineBasicBlock::iterator &MBBI) {
   return false;
 }
 
-// Merge two adjacent load/store instructions into a paired instruction
-// (LDP/SDP/SWP/LWP) if the effective address is 8-byte aligned in case of
-// SWP/LWP 16-byte aligned in case of LDP/SDP. This function selects the
-// appropriate paired opcode, verifies that the memory operand is properly
-// aligned, and checks that the offset is valid. If all conditions are met, it
-// builds and inserts the paired instruction.
-bool RISCVLoadStoreOpt::tryConvertToLdStPair(
-    MachineBasicBlock::iterator First, MachineBasicBlock::iterator Second) {
+bool RISCVLoadStoreOpt::tryConvertToXqcilsmLdStPair(
+    MachineFunction *MF, MachineBasicBlock::iterator First,
+    MachineBasicBlock::iterator Second) {
+  unsigned Opc = First->getOpcode();
+  if ((Opc != RISCV::LW && Opc != RISCV::SW) || Second->getOpcode() != Opc)
+    return false;
+
+  const auto &FirstOp1 = First->getOperand(1);
+  const auto &SecondOp1 = Second->getOperand(1);
+  const auto &FirstOp2 = First->getOperand(2);
+  const auto &SecondOp2 = Second->getOperand(2);
+
+  // Require simple reg+imm addressing for both.
+  if (!FirstOp1.isReg() || !SecondOp1.isReg() || !FirstOp2.isImm() ||
+      !SecondOp2.isImm())
+    return false;
+
+  Register Base1 = FirstOp1.getReg();
+  Register Base2 = SecondOp1.getReg();
+
+  if (Base1 != Base2)
+    return false;
+
+  const MachineMemOperand *MMO = *First->memoperands_begin();
+  Align MMOAlign = MMO->getAlign();
+
+  if (MMOAlign < Align(4))
+    return false;
+
+  auto &FirstOp0 = First->getOperand(0);
+  auto &SecondOp0 = Second->getOperand(0);
+
+  int64_t Off1 = FirstOp2.getImm();
+  int64_t Off2 = SecondOp2.getImm();
+
+  if (Off2 < Off1) {
+    std::swap(FirstOp0, SecondOp0);
+    std::swap(Off1, Off2);
+  }
+
+  Register StartReg = FirstOp0.getReg();
+  Register NextReg = SecondOp0.getReg();
+
+  if (StartReg == RISCV::X0 || NextReg == RISCV::X0)
+    return false;
+
+  // If the base reg gets overwritten by one of the loads then bail out.
+  if (Opc == RISCV::LW && (StartReg == Base1 || NextReg == Base1))
+    return false;
+
+  if (!isShiftedUInt<5, 2>(Off1) || (Off2 - Off1 != 4))
+    return false;
+
+  if (NextReg != StartReg + 1)
+    return false;
+
+  unsigned XqciOpc = (Opc == RISCV::LW) ? RISCV::QC_LWMI : RISCV::QC_SWMI;
+
+  auto StartRegState = (Opc == RISCV::LW) ? RegState::Define
+                                          : getKillRegState(FirstOp0.isKill());
+  auto NextRegState =
+      (Opc == RISCV::LW)
+          ? RegState::ImplicitDefine
+          : (RegState::Implicit | getKillRegState(SecondOp0.isKill()));
+
+  DebugLoc DL =
+      First->getDebugLoc() ? First->getDebugLoc() : Second->getDebugLoc();
+  MachineInstrBuilder MIB = BuildMI(*MF, DL, TII->get(XqciOpc));
+  MIB.addReg(StartReg, StartRegState)
+      .addReg(Base1, getKillRegState(FirstOp1.isKill() || SecondOp1.isKill()))
+      .addImm(2)
+      .addImm(Off1)
+      .cloneMergedMemRefs({&*First, &*Second})
+      .addReg(NextReg, NextRegState);
+
+  First->getParent()->insert(First, MIB);
+  First->removeFromParent();
+  Second->removeFromParent();
+
+  return true;
+}
+
+bool RISCVLoadStoreOpt::tryConvertToMIPSLdStPair(
+    MachineFunction *MF, MachineBasicBlock::iterator First,
+    MachineBasicBlock::iterator Second) {
+  // Try converting to SWP/LWP/LDP/SDP.
+  // SWP/LWP requires 8-byte alignment whereas LDP/SDP needs 16-byte alignment.
   unsigned PairOpc;
   Align RequiredAlignment;
   switch (First->getOpcode()) {
@@ -199,7 +284,6 @@ bool RISCVLoadStoreOpt::tryConvertToLdStPair(
     break;
   }
 
-  MachineFunction *MF = First->getMF();
   const MachineMemOperand *MMO = *First->memoperands_begin();
   Align MMOAlign = MMO->getAlign();
 
@@ -227,6 +311,24 @@ bool RISCVLoadStoreOpt::tryConvertToLdStPair(
   return true;
 }
 
+// Merge two adjacent load/store instructions into a paired instruction.
+// This function calls the vendor specific implementation that seelects the
+// appropriate paired opcode, verifies that the memory operand is properly
+// aligned, and checks that the offset is valid. If all conditions are met, it
+// builds and inserts the paired instruction.
+bool RISCVLoadStoreOpt::tryConvertToLdStPair(
+    MachineBasicBlock::iterator First, MachineBasicBlock::iterator Second) {
+  MachineFunction *MF = First->getMF();
+  const RISCVSubtarget &STI = MF->getSubtarget<RISCVSubtarget>();
+
+  // Try converting to QC_LWMI/QC_SWMI if the XQCILSM extension is enabled.
+  if (!STI.is64Bit() && STI.hasVendorXqcilsm())
+    return tryConvertToXqcilsmLdStPair(MF, First, Second);
+
+  // Else try to convert them into MIPS Paired Loads/Stores.
+  return tryConvertToMIPSLdStPair(MF, First, Second);
+}
+
 static bool mayAlias(MachineInstr &MIa,
                      SmallVectorImpl<MachineInstr *> &MemInsns,
                      AliasAnalysis *AA) {