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

[Stefan Pintilie via llvm-commits]

================
@@ -7565,224 +7565,205 @@ 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();
+static void peepholeMemOffset(SDNode *N, SelectionDAG *DAG,
+                              const PPCSubtarget *Subtarget) {
+  unsigned StorageOpcode = N->getMachineOpcode();
+  bool IsLoad = false;
+  SDValue MemOffset, MemBase;
 
-  while (Position != CurDAG->allnodes_begin()) {
-    SDNode *N = &*--Position;
-    // Skip dead nodes and any non-machine opcodes.
-    if (N->use_empty() || !N->isMachineOpcode())
-      continue;
-
-    if (isVSXSwap(SDValue(N, 0)))
-      reduceVSXSwap(N, CurDAG);
-
-    unsigned FirstOp;
-    unsigned StorageOpcode = N->getMachineOpcode();
-    bool RequiresMod4Offset = false;
-
-    switch (StorageOpcode) {
-    default: continue;
+  // TODO: Enable for AIX 32-bit
+  if (!Subtarget->isPPC64())
+    return;
 
-    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;
+  // Global must be word-aligned for LD, STD, LWA.
+  unsigned ExtraAlign = 0;
+  switch (StorageOpcode) {
+  default:
+    return;
+  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;
+    MemOffset = N->getOperand(0);
+    MemBase = N->getOperand(1);
+    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:
+    MemOffset = N->getOperand(1);
+    MemBase = N->getOperand(2);
+    break;
+  }
 
-    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 (TargetAlign == 0)
+      return true;
----------------
stefanp-ibm wrote:

You don't really need this special case. You are dealing with only unsigned values here. `llvm::Align` and `TargetAlign` are both unsigned. The if statement:
```
      if (Alignment < TargetAlign)
        return false;
```
should work for both.

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