ppc64: [baseline] implement AddSmi

Change-Id: I94f3f02e2214437d8320d31c8be24f41698f136c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3604752Reviewed-by: Milad Farazmand <mfarazma@redhat.com>
Commit-Queue: Junliang Yan <junyan@redhat.com>
Cr-Commit-Position: refs/heads/main@{#80156}

src/baseline/ppc/baseline-assembler-ppc-inl.h

@@ -578,7 +578,15 @@ void BaselineAssembler::AddToInterruptBudgetAndJumpIfNotExceeded(
   if (skip_interrupt_label) __ b(ge, skip_interrupt_label);
 }
 
-void BaselineAssembler::AddSmi(Register lhs, Smi rhs) { UNIMPLEMENTED(); }
+void BaselineAssembler::AddSmi(Register lhs, Smi rhs) {
+  if (rhs.value() == 0) return;
+  __ LoadSmiLiteral(r0, rhs);
+  if (SmiValuesAre31Bits()) {
+    __ AddS32(lhs, lhs, r0);
+  } else {
+    __ AddS64(lhs, lhs, r0);
+  }
+}
 
 void BaselineAssembler::Switch(Register reg, int case_value_base,
                                Label** labels, int num_labels) {