[strong] Function arity check should be based on required parameters

src/mips64/builtins-mips64.cc

Index: src/mips64/builtins-mips64.cc
diff --git a/src/mips64/builtins-mips64.cc b/src/mips64/builtins-mips64.cc
index 2c2233256b17059fb0829f596977b1ee29c09147..c7d4574c6c9382a6730c4bce18c827dcb12ab8a5 100644
--- a/src/mips64/builtins-mips64.cc
+++ b/src/mips64/builtins-mips64.cc
@@ -1753,11 +1753,16 @@ void Builtins::Generate_ArgumentsAdaptorTrampoline(MacroAssembler* masm) {
     __ bind(&too_few);
 
     // If the function is strong we need to throw an error.
-    Label weak_function;
+    Label no_strong_error;
     __ ld(a4, FieldMemOperand(a1, JSFunction::kSharedFunctionInfoOffset));
-    __ lbu(a4, FieldMemOperand(a4, SharedFunctionInfo::kStrongModeByteOffset));
-    __ And(a4, a4, Operand(1 << SharedFunctionInfo::kStrongModeBitWithinByte));
-    __ Branch(&weak_function, eq, a4, Operand(zero_reg));
+    __ lbu(a5, FieldMemOperand(a4, SharedFunctionInfo::kStrongModeByteOffset));
+    __ And(a5, a5, Operand(1 << SharedFunctionInfo::kStrongModeBitWithinByte));
+    __ Branch(&no_strong_error, eq, a5, Operand(zero_reg));
+
+    // What we really care about is the required number of arguments.
+    __ lw(a5, FieldMemOperand(a4, SharedFunctionInfo::kLengthOffset));
+    __ srl(a5, a5, 1);

[paul.l..., 2015/05/18 22:04:01]

A couple nits that I think are completely unimportant for this usage: lw() will
sign extend (lwu() will zero-extend). If you expect negative numbers then your
shift should be sra(). Since this is a parameter count, it won't be negative,
and it won't be close to 2^31 so I don't think either comment applies here.

[paul.l..., 2015/05/18 22:11:47]

Actually, if you expected negative numbers, you should then use dsra(), the
double-word/64-bit arithmetic shift. Still a nit for this usage.

+    __ Branch(&no_strong_error, ge, a0, Operand(a5));
 
     {
       FrameScope frame(masm, StackFrame::MANUAL);
@@ -1765,7 +1770,7 @@ void Builtins::Generate_ArgumentsAdaptorTrampoline(MacroAssembler* masm) {
       __ CallRuntime(Runtime::kThrowStrongModeTooFewArguments, 0);
     }
 
-    __ bind(&weak_function);
+    __ bind(&no_strong_error);
     EnterArgumentsAdaptorFrame(masm);
 
     // Calculate copy start address into a0 and copy end address is fp.