PPC: [runtime] Implement %_ToLength via ToLengthStub.

Port e678a0f9

Original commit message:
    Use %_ToLength for TO_LENGTH, implemented via a ToLengthStub
    that supports a fast path for small integers. Everything else is still
    handled in the runtime.

R=bmeurer@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, dstence@us.ibm.com
BUG=v8:4494
LOG=n

Review URL: https://codereview.chromium.org/1412153003

Cr-Commit-Position: refs/heads/master@{#31384}

src/ppc/code-stubs-ppc.cc

@@ -3334,6 +3334,28 @@ void ToNumberStub::Generate(MacroAssembler* masm) {
 }
 
 
+void ToLengthStub::Generate(MacroAssembler* masm) {
+  // The ToLength stub takes one argument in r3.
+  Label not_smi;
+  __ JumpIfNotSmi(r3, &not_smi);
+  STATIC_ASSERT(kSmiTag == 0);
+  __ cmpi(r3, Operand::Zero());
+  if (CpuFeatures::IsSupported(ISELECT)) {
+    __ isel(lt, r3, r0, r3);
+  } else {
+    Label positive;
+    __ bgt(&positive);
+    __ li(r3, Operand::Zero());
+    __ bind(&positive);
+  }
+  __ Ret();
+  __ bind(&not_smi);
+
+  __ push(r3);  // Push argument.
+  __ TailCallRuntime(Runtime::kToLength, 1, 1);
+}
+
+
 void ToStringStub::Generate(MacroAssembler* masm) {
   // The ToString stub takes one argument in r3.
   Label is_number;

src/ppc/interface-descriptors-ppc.cc

@@ -99,6 +99,10 @@ void ToNumberDescriptor::InitializePlatformSpecific(
 }
 
 
+// static
+const Register ToLengthDescriptor::ReceiverRegister() { return r3; }
+
+
 // static
 const Register ToStringDescriptor::ReceiverRegister() { return r3; }