fixup: Improve fix flags and use MIPS pariable instrs only

Author: djtodoro

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -2750,21 +2750,17 @@ MachineInstr *RISCVInstrInfo::emitLdStWithAddr(MachineInstr &MemI,
       .setMIFlags(MemI.getFlags());
 }
 
+// TODO: At the moment, MIPS introduced paring of instructions operating with
+// word or double word. This should be extended with more instructions when more
+// vendors support load/store pairing.
 bool RISCVInstrInfo::isPairableLdStInstOpc(unsigned Opc) {
   switch (Opc) {
   default:
     return false;
-  case RISCV::SH:
-  case RISCV::LH:
-  case RISCV::LHU:
   case RISCV::SW:
-  case RISCV::FSW:
-  case RISCV::LW:
-  case RISCV::FLW:
   case RISCV::SD:
-  case RISCV::FSD:
   case RISCV::LD:
-  case RISCV::FLD:
+  case RISCV::LW:
     return true;
   }
 }

llvm/lib/Target/RISCV/RISCVLoadStoreOptimizer.cpp

@@ -151,11 +151,10 @@ bool RISCVLoadStoreOpt::tryToPairLdStInst(MachineBasicBlock::iterator &MBBI) {
 bool RISCVLoadStoreOpt::tryConvertToLdStPair(
     MachineBasicBlock::iterator First, MachineBasicBlock::iterator Second) {
   unsigned PairOpc;
-  // TODO: Handle the rest from RISCVInstrInfo::isPairableLdStInstOpc.
   Align RequiredAlignment;
   switch (First->getOpcode()) {
   default:
-    return false;
+    llvm_unreachable("Unsupported load/store instruction for pairing");
   case RISCV::SW:
     PairOpc = RISCV::MIPS_SWP;
     RequiredAlignment = Align(8);
@@ -178,13 +177,11 @@ bool RISCVLoadStoreOpt::tryConvertToLdStPair(
   const MachineMemOperand *MMO = *First->memoperands_begin();
   Align MMOAlign = MMO->getAlign();
 
-  // Only pair if alignment is exactly RequiredAlignment bytes.
-  if (MMOAlign != RequiredAlignment)
+  if (MMOAlign < RequiredAlignment)
     return false;
 
   int64_t Offset = First->getOperand(2).getImm();
-  if (!isUInt<7>(Offset) ||
-      !isAligned(Align(MMO->getSize().getValue()), Offset))
+  if (!isUInt<7>(Offset))
     return false;
 
   MachineInstrBuilder MIB = BuildMI(
@@ -360,11 +357,20 @@ RISCVLoadStoreOpt::mergePairedInsns(MachineBasicBlock::iterator I,
   // Kill flags may become invalid when moving stores for pairing.
   if (I->getOperand(0).isUse()) {
     if (!MergeForward) {
-      // Clear kill flags on store if moving upwards.
-      I->getOperand(0).setIsKill(false);
-      Paired->getOperand(0).setIsKill(false);
+      // Check if the Paired store's source register has a kill flag and clear
+      // it only if there are intermediate uses between I and Paired.
+      MachineOperand &PairedRegOp = Paired->getOperand(0);
+      if (PairedRegOp.isKill()) {
+        for (auto It = std::next(I); It != Paired; ++It) {
+          if (It->readsRegister(PairedRegOp.getReg(), TRI)) {
+            PairedRegOp.setIsKill(false);
+            break;
+          }
+        }
+      }
     } else {
-      // Clear kill flags of the first stores register.
+      // Clear kill flags of the first store's register in the forward
+      // direction.
       Register Reg = I->getOperand(0).getReg();
       for (MachineInstr &MI : make_range(std::next(I), std::next(Paired)))
         MI.clearRegisterKills(Reg, TRI);

llvm/test/CodeGen/RISCV/load-store-pair.ll

@@ -153,8 +153,7 @@ define dso_local void @testi(i8** nocapture noundef readonly %a) local_unnamed_a
 ; RV32I_PAIR-NEXT:    .cfi_offset s3, -8
 ; RV32I_PAIR-NEXT:    .cfi_offset s4, -12
 ; RV32I_PAIR-NEXT:    .cfi_offset s5, -16
-; RV32I_PAIR-NEXT:    lw s3, 0(a0)
-; RV32I_PAIR-NEXT:    lw s2, 4(a0)
+; RV32I_PAIR-NEXT:    mips.lwp s3, s2, 0(a0)
 ; RV32I_PAIR-NEXT:    mips.lwp s5, s4, 8(a0)
 ; RV32I_PAIR-NEXT:    #APP
 ; RV32I_PAIR-NEXT:    #NO_APP
@@ -182,8 +181,7 @@ define dso_local void @testi(i8** nocapture noundef readonly %a) local_unnamed_a
 ; RV32D_PAIR-NEXT:    .cfi_offset s3, -8
 ; RV32D_PAIR-NEXT:    .cfi_offset s4, -12
 ; RV32D_PAIR-NEXT:    .cfi_offset s5, -16
-; RV32D_PAIR-NEXT:    lw s3, 0(a0)
-; RV32D_PAIR-NEXT:    lw s2, 4(a0)
+; RV32D_PAIR-NEXT:    mips.lwp s3, s2, 0(a0)
 ; RV32D_PAIR-NEXT:    mips.lwp s5, s4, 8(a0)
 ; RV32D_PAIR-NEXT:    #APP
 ; RV32D_PAIR-NEXT:    #NO_APP