[turbofan] Reland of `Add alignment parameter to StackSlot operator`

src/compiler/ppc/instruction-selector-ppc.cc

Index: src/compiler/ppc/instruction-selector-ppc.cc
diff --git a/src/compiler/ppc/instruction-selector-ppc.cc b/src/compiler/ppc/instruction-selector-ppc.cc
index 449e71038999032df537ebc2d332fd8607f3283e..ea88e81a05ed6c12192c38ab96c3f28381db83f3 100644
--- a/src/compiler/ppc/instruction-selector-ppc.cc
+++ b/src/compiler/ppc/instruction-selector-ppc.cc
@@ -174,6 +174,14 @@ void VisitBinop(InstructionSelector* selector, Node* node,
 
 }  // namespace
 
+void InstructionSelector::VisitStackSlot(Node* node) {
+  StackSlotRepresentation rep = StackSlotRepresentationOf(node->op());
+  int slot = frame_->AllocateSpillSlot(rep.size());
+  OperandGenerator g(this);
+
+  Emit(kArchStackSlot, g.DefineAsRegister(node),
+       sequence()->AddImmediate(Constant(slot)), 0, nullptr);
+}
 
 void InstructionSelector::VisitLoad(Node* node) {
   LoadRepresentation load_rep = LoadRepresentationOf(node->op());