[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
----------------
amy-kwan wrote:

- Nit: end with period.
- Also, if we enable for 32-bit, this is going into a function called `PeepholePPC64()`. Not sure if the function name is still appropriate in that case.

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