[llvm] [PowerPC] Peephole address calculation in TOC memops (PR #76488)

[Amy Kwan via llvm-commits]

================
@@ -7565,224 +7565,209 @@ static void reduceVSXSwap(SDNode *N, SelectionDAG *DAG) {
   DAG->ReplaceAllUsesOfValueWith(SDValue(N, 0), N->getOperand(0));
 }
 
-void PPCDAGToDAGISel::PeepholePPC64() {
-  SelectionDAG::allnodes_iterator Position = CurDAG->allnodes_end();
-
-  while (Position != CurDAG->allnodes_begin()) {
-    SDNode *N = &*--Position;
-    // Skip dead nodes and any non-machine opcodes.
-    if (N->use_empty() || !N->isMachineOpcode())
-      continue;
+static bool isValidOffsetMemOp(SDNode *N, bool &IsLoad, unsigned &ExtraAlign) {
+  switch (N->getMachineOpcode()) {
+  default:
+    return false;
+  // Global must be word-aligned for LD, STD, LWA.
+  case PPC::LWA:
+  case PPC::LD:
+  case PPC::DFLOADf64:
+  case PPC::DFLOADf32:
+    ExtraAlign = 4;
+    [[fallthrough]];
+  case PPC::LBZ:
+  case PPC::LBZ8:
+  case PPC::LFD:
+  case PPC::LFS:
+  case PPC::LHA:
+  case PPC::LHA8:
+  case PPC::LHZ:
+  case PPC::LHZ8:
+  case PPC::LWZ:
+  case PPC::LWZ8:
+    IsLoad = true;
+    break;
+  case PPC::STD:
+  case PPC::DFSTOREf64:
+  case PPC::DFSTOREf32:
+    ExtraAlign = 4;
+    [[fallthrough]];
+  case PPC::STB:
+  case PPC::STB8:
+  case PPC::STFD:
+  case PPC::STFS:
+  case PPC::STH:
+  case PPC::STH8:
+  case PPC::STW:
+  case PPC::STW8:
+    break;
+  }
+  SDValue Base = N->getOperand(IsLoad ? 1 : 2);
+  if (!Base.isMachineOpcode())
+    return false;
+  switch (Base.getMachineOpcode()) {
+  default:
+    return false;
+  case PPC::ADDI8:
+  case PPC::ADDI:
+  case PPC::ADDIdtprelL:
+  case PPC::ADDItlsldL:
+  case PPC::ADDItocL:
+  case PPC::ADDItoc:
+  case PPC::ADDItoc8:
+    break;
+  }
+  return true;
+}
 
-    if (isVSXSwap(SDValue(N, 0)))
-      reduceVSXSwap(N, CurDAG);
+static void peepholeMemOffset(SDNode *N, SelectionDAG *DAG,
+                              const PPCSubtarget *Subtarget) {
+  // TODO: Enable for AIX 32-bit
+  if (!Subtarget->isPPC64())
+    return;
 
-    unsigned FirstOp;
-    unsigned StorageOpcode = N->getMachineOpcode();
-    bool RequiresMod4Offset = false;
+  bool IsLoad = false;
+  unsigned ExtraAlign = 1;
+  if (!isValidOffsetMemOp(N, IsLoad, ExtraAlign))
+    return;
 
-    switch (StorageOpcode) {
-    default: continue;
+  SDValue MemOffset = N->getOperand(IsLoad ? 0 : 1);
+  SDValue MemBase = N->getOperand(IsLoad ? 1 : 2);
+  unsigned BaseOpc = MemBase.getMachineOpcode();
 
-    case PPC::LWA:
-    case PPC::LD:
-    case PPC::DFLOADf64:
-    case PPC::DFLOADf32:
-      RequiresMod4Offset = true;
-      [[fallthrough]];
-    case PPC::LBZ:
-    case PPC::LBZ8:
-    case PPC::LFD:
-    case PPC::LFS:
-    case PPC::LHA:
-    case PPC::LHA8:
-    case PPC::LHZ:
-    case PPC::LHZ8:
-    case PPC::LWZ:
-    case PPC::LWZ8:
-      FirstOp = 0;
-      break;
+  // Only additions with constant offsets will be folded.
+  if (!isa<ConstantSDNode>(MemOffset))
+    return;
+  assert(MemBase.getNumOperands() == 2 && "Invalid base of memop with offset!");
 
-    case PPC::STD:
-    case PPC::DFSTOREf64:
-    case PPC::DFSTOREf32:
-      RequiresMod4Offset = true;
-      [[fallthrough]];
-    case PPC::STB:
-    case PPC::STB8:
-    case PPC::STFD:
-    case PPC::STFS:
-    case PPC::STH:
-    case PPC::STH8:
-    case PPC::STW:
-    case PPC::STW8:
-      FirstOp = 1;
-      break;
+  auto CheckAlign = [DAG](const SDValue &Val, unsigned TargetAlign) {
+    if (GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(Val)) {
+      Align Alignment =
+          GA->getGlobal()->getPointerAlignment(DAG->getDataLayout());
+      if (Alignment < TargetAlign)
+        return false;
     }
+    return true;
+  };
 
-    // If this is a load or store with a zero offset, or within the alignment,
-    // we may be able to fold an add-immediate into the memory operation.
-    // The check against alignment is below, as it can't occur until we check
-    // the arguments to N
-    if (!isa<ConstantSDNode>(N->getOperand(FirstOp)))
-      continue;
-
-    SDValue Base = N->getOperand(FirstOp + 1);
-    if (!Base.isMachineOpcode())
-      continue;
-
-    unsigned Flags = 0;
-    bool ReplaceFlags = true;
+  SDValue ImmOp, RegOp;
+  // ADDItoc and ADDItoc8 (prints 'la') put register at second operand.
----------------
amy-kwan wrote:

Nit on the sentence.
```suggestion
  // ADDItoc and ADDItoc8 (prints 'la') puts the register at the second operand.
```

https://github.com/llvm/llvm-project/pull/76488