[llvm] [AArch64] Optimize when storing symmetry constants (PR #93717)

[David Green via llvm-commits]

================
@@ -2252,6 +2260,159 @@ MachineBasicBlock::iterator AArch64LoadStoreOpt::findMatchingUpdateInsnBackward(
   return E;
 }
 
+static bool isSymmetric(MachineInstr &MI, Register BaseReg) {
+  auto MatchBaseReg = [&](unsigned Count) {
+    for (unsigned I = 0; I < Count; I++) {
+      auto OpI = MI.getOperand(I);
+      if (OpI.isReg() && OpI.getReg() != BaseReg)
+        return false;
+    }
+    return true;
+  };
+
+  unsigned Opc = MI.getOpcode();
+  switch (Opc) {
+  default:
+    return false;
+  case AArch64::MOVZXi:
+    return MatchBaseReg(1);
+  case AArch64::MOVKXi:
+    return MatchBaseReg(2);
+  case AArch64::ORRXrs:
+    MachineOperand &Imm = MI.getOperand(3);
+    // Fourth operand of ORR must be 32 which mean
+    // 32bit symmetric constant load.
+    // ex) renamable $x8 = ORRXrs $x8, $x8, 32
+    if (MatchBaseReg(3) && Imm.isImm() && Imm.getImm() == 32)
+      return true;
+  }
+
+  return false;
+}
+
+MachineBasicBlock::iterator AArch64LoadStoreOpt::doFoldSymmetryConstantLoad(
+    MachineInstr &MI, SmallVectorImpl<MachineBasicBlock::iterator> &MIs,
+    int SuccIndex, int Accumulated) {
+  MachineBasicBlock::iterator I = MI.getIterator();
+  MachineBasicBlock::iterator E = I->getParent()->end();
+  MachineBasicBlock::iterator NextI = next_nodbg(I, E);
+  MachineBasicBlock::iterator FirstMovI;
+  MachineBasicBlock *MBB = MI.getParent();
+  uint64_t Mask = 0xFFFFUL;
+  int Index = 0;
+
+  for (auto MI = MIs.begin(), E = MIs.end(); MI != E; ++MI, Index++) {
+    if (Index == SuccIndex - 1) {
+      FirstMovI = *MI;
+      break;
+    }
+    (*MI)->eraseFromParent();
+  }
+
+  Register DstRegW =
+      TRI->getSubReg(FirstMovI->getOperand(0).getReg(), AArch64::sub_32);
+  int Lower = Accumulated & Mask;
+  if (Lower) {
+    BuildMI(*MBB, FirstMovI, FirstMovI->getDebugLoc(),
+            TII->get(AArch64::MOVZWi), DstRegW)
+        .addImm(Lower)
+        .addImm(0);
+    Lower = Accumulated >> 16 & Mask;
----------------
davemgreen wrote:

 (Accumulated >> 16) & Mask;

https://github.com/llvm/llvm-project/pull/93717