S390: optimize loading of reversed bytes

This adds a check similar to Word32ReverseBytes.

Change-Id: I3a75f29ae1b9cb75dd0fda471d6d42ca21915bf9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3009795Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/master@{#75591}

src/compiler/backend/s390/instruction-selector-s390.cc

@@ -1084,6 +1084,19 @@ void InstructionSelector::VisitInt64AbsWithOverflow(Node* node) {
 
 void InstructionSelector::VisitWord64ReverseBytes(Node* node) {
   S390OperandGenerator g(this);
+  NodeMatcher input(node->InputAt(0));
+  if (CanCover(node, input.node()) && input.IsLoad()) {
+    LoadRepresentation load_rep = LoadRepresentationOf(input.node()->op());
+    if (load_rep.representation() == MachineRepresentation::kWord64) {
+      Node* base = input.node()->InputAt(0);
+      Node* offset = input.node()->InputAt(1);
+      Emit(kS390_LoadReverse64 | AddressingModeField::encode(kMode_MRR),
+           // TODO(miladfarca): one of the base and offset can be imm.
+           g.DefineAsRegister(node), g.UseRegister(base),
+           g.UseRegister(offset));
+      return;
+    }
+  }
   Emit(kS390_LoadReverse64RR, g.DefineAsRegister(node),
        g.UseRegister(node->InputAt(0)));
 }