PPC: [crankshaft] Support ES6 tail call elimination.

src/ppc/macro-assembler-ppc.cc

Index: src/ppc/macro-assembler-ppc.cc
diff --git a/src/ppc/macro-assembler-ppc.cc b/src/ppc/macro-assembler-ppc.cc
index 14759de0da334b700d2f96e720489672948b493b..3f8640a408fdf9b9393c78c164d387705424c0a9 100644
--- a/src/ppc/macro-assembler-ppc.cc
+++ b/src/ppc/macro-assembler-ppc.cc
@@ -1093,6 +1093,67 @@ void MacroAssembler::MovFromFloatParameter(const DoubleRegister dst) {
   Move(dst, d1);
 }
 
+void MacroAssembler::PrepareForTailCall(const ParameterCount& callee_args_count,
+                                        Register caller_args_count_reg,
+                                        Register scratch0, Register scratch1) {
+#if DEBUG
+  if (callee_args_count.is_reg()) {
+    DCHECK(!AreAliased(callee_args_count.reg(), caller_args_count_reg, scratch0,
+                       scratch1));
+  } else {
+    DCHECK(!AreAliased(caller_args_count_reg, scratch0, scratch1));
+  }
+#endif
+
+  // Calculate the end of destination area where we will put the arguments
+  // after we drop current frame. We add kPointerSize to count the receiver
+  // argument which is not included into formal parameters count.
+  Register dst_reg = scratch0;
+  ShiftLeftImm(dst_reg, caller_args_count_reg, Operand(kPointerSizeLog2));
+  add(dst_reg, fp, dst_reg);
+  addi(dst_reg, dst_reg,
+       Operand(StandardFrameConstants::kCallerSPOffset + kPointerSize));
+
+  Register src_reg = caller_args_count_reg;
+  // Calculate the end of source area. +kPointerSize is for the receiver.
+  if (callee_args_count.is_reg()) {
+    ShiftLeftImm(src_reg, callee_args_count.reg(), Operand(kPointerSizeLog2));
+    add(src_reg, sp, src_reg);
+    addi(src_reg, src_reg, Operand(kPointerSize));
+  } else {
+    Add(src_reg, sp, (callee_args_count.immediate() + 1) * kPointerSize, r0);
+  }
+
+  if (FLAG_debug_code) {
+    cmpl(src_reg, dst_reg);
+    Check(lt, kStackAccessBelowStackPointer);
+  }
+
+  // Restore caller's frame pointer and return address now as they will be
+  // overwritten by the copying loop.
+  RestoreFrameStateForTailCall();
+
+  // Now copy callee arguments to the caller frame going backwards to avoid
+  // callee arguments corruption (source and destination areas could overlap).
+
+  // Both src_reg and dst_reg are pointing to the word after the one to copy,
+  // so they must be pre-decremented in the loop.
+  Register tmp_reg = scratch1;
+  Label loop;
+  if (callee_args_count.is_reg()) {
+    addi(tmp_reg, callee_args_count.reg(), Operand(1));  // +1 for receiver
+  } else {
+    mov(tmp_reg, Operand(callee_args_count.immediate() + 1));
+  }
+  mtctr(tmp_reg);
+  bind(&loop);
+  LoadPU(tmp_reg, MemOperand(src_reg, -kPointerSize));
+  StorePU(tmp_reg, MemOperand(dst_reg, -kPointerSize));
+  bdnz(&loop);
+
+  // Leave current frame.
+  mr(sp, dst_reg);
+}
 
 void MacroAssembler::InvokePrologue(const ParameterCount& expected,
                                     const ParameterCount& actual, Label* done,