[wasm] Support validation of asm.js modules with != 3 args.

src/builtins/ppc/builtins-ppc.cc

Index: src/builtins/ppc/builtins-ppc.cc
diff --git a/src/builtins/ppc/builtins-ppc.cc b/src/builtins/ppc/builtins-ppc.cc
index ef01f40b6eee0bff9c548ecad65977a0dd8d95c1..b799819dbdf71b5af1394eb4079d63761213bddb 100644
--- a/src/builtins/ppc/builtins-ppc.cc
+++ b/src/builtins/ppc/builtins-ppc.cc
@@ -1458,23 +1458,47 @@ void Builtins::Generate_InstantiateAsmJs(MacroAssembler* masm) {
   Label failed;
   {
     FrameScope scope(masm, StackFrame::INTERNAL);
+    // Preserve argument count for later compare.
+    __ Move(r5, r3);
     // Push a copy of the target function and the new target.
     // Push function as parameter to the runtime call.
     __ SmiTag(r3);
     __ Push(r3, r4, r6, r4);
 
     // Copy arguments from caller (stdlib, foreign, heap).
-    for (int i = 2; i >= 0; --i) {
-      __ LoadP(r4, MemOperand(fp, StandardFrameConstants::kCallerSPOffset +
-                                      i * kPointerSize));
-      __ push(r4);
+    Label args_done;
+    for (int j = 0; j < 4; ++j) {
+      Label over;
+      if (j < 3) {
+        __ cmpi(r5, Operand(j));
+        __ bne(&over);
+      }
+      for (int i = j - 1; i >= 0; --i) {
+        __ LoadP(r5, MemOperand(fp, StandardFrameConstants::kCallerSPOffset +
+                                        i * kPointerSize));
+        __ push(r5);
+      }
+      for (int i = 0; i < 3 - j; ++i) {
+        __ PushRoot(Heap::kUndefinedValueRootIndex);
+      }
+      if (j < 3) {
+        __ jmp(&args_done);
+        __ bind(&over);
+      }
     }
+    __ bind(&args_done);
+
     // Call runtime, on success unwind frame, and parent frame.
     __ CallRuntime(Runtime::kInstantiateAsmJs, 4);
     // A smi 0 is returned on failure, an object on success.
     __ JumpIfSmi(r3, &failed);
+
+    __ Drop(2);
+    __ pop(r5);
+    __ SmiUntag(r5);
     scope.GenerateLeaveFrame();
-    __ Drop(4);
+
+    __ Drop(r5);
     __ Ret();
 
     __ bind(&failed);