PPC: [builtins] Make sure argument count is always valid for C++ builtins.

src/ppc/builtins-ppc.cc

Index: src/ppc/builtins-ppc.cc
diff --git a/src/ppc/builtins-ppc.cc b/src/ppc/builtins-ppc.cc
index 7269b18b4c11a90fdec76da24ada712e91aa0b5f..cdbb1c24a076d7446d8ab230bd1f110ccc9be9da 100644
--- a/src/ppc/builtins-ppc.cc
+++ b/src/ppc/builtins-ppc.cc
@@ -21,11 +21,12 @@ void Builtins::Generate_Adaptor(MacroAssembler* masm, CFunctionId id,
                                 BuiltinExtraArguments extra_args) {
   // ----------- S t a t e -------------
   //  -- r3                 : number of arguments excluding receiver
-  //  -- r4                 : called function (only guaranteed when
-  //                          extra_args requires it)
+  //                          (only guaranteed when the called function
+  //                           is not marked as DontAdaptArguments)
+  //  -- r4                 : called function
   //  -- sp[0]              : last argument
   //  -- ...
-  //  -- sp[4 * (argc - 1)] : first argument (argc == r0)
+  //  -- sp[4 * (argc - 1)] : first argument
   //  -- sp[4 * argc]       : receiver
   // -----------------------------------
   __ AssertFunction(r4);
@@ -46,9 +47,27 @@ void Builtins::Generate_Adaptor(MacroAssembler* masm, CFunctionId id,
     DCHECK(extra_args == NO_EXTRA_ARGUMENTS);
   }
 
-  // JumpToExternalReference expects r0 to contain the number of arguments
-  // including the receiver and the extra arguments.
+  // JumpToExternalReference expects r3 to contain the number of arguments
+  // including the receiver and the extra arguments.  But r3 is only valid
+  // if the called function is marked as DontAdaptArguments, otherwise we
+  // need to load the argument count from the SharedFunctionInfo.
+  __ LoadP(r5, FieldMemOperand(r4, JSFunction::kSharedFunctionInfoOffset));
+  __ LoadWordArith(
+      r5, FieldMemOperand(r5, SharedFunctionInfo::kFormalParameterCountOffset));
+#if !V8_TARGET_ARCH_PPC64
+  __ SmiUntag(r5);
+#endif
+  __ cmpi(r5, Operand(SharedFunctionInfo::kDontAdaptArgumentsSentinel));
+  if (CpuFeatures::IsSupported(ISELECT)) {
+    __ isel(ne, r3, r5, r3);
+  } else {
+    Label skip;
+    __ beq(&skip);
+    __ mr(r3, r5);
+    __ bind(&skip);
+  }
   __ addi(r3, r3, Operand(num_extra_args + 1));
+
   __ JumpToExternalReference(ExternalReference(id, masm->isolate()));
 }