[LLVMdev] RFC: Tailcall Improvement

Evan Cheng
Fri, 11 Jan 2008 00:16:28 -0000

1. IsPossiblyOverriddenArgumentOfTailCall() should be marked static?

2. Please start all function level comments this way:
// IsPossiblyOverriddenArgumentOfTailCall - Check if ...

3.
+        if (IsPossiblyOverriddenArgumentOfTailCall(Arg)){
+          // Copy from stack slots to stack slot of a tail called
function. This
+          // needs to be done because if we would lower the arguments
directly
+          // to their real stack slot we might end up overwriting
each other.
+          // Get source stack slot.
+          Source = DAG.getConstant(VA.getLocMemOffset(),
+                                             getPointerTy());
Funky indentation?

4.
+          if (StackPtr.Val == 0)
+            StackPtr = DAG.getRegister(getStackPtrReg(),
getPointerTy());

This should be a CopyFromReg which reads the stack pointer register.

5.

+        SDOperand Source;
+        if (IsPossiblyOverriddenArgumentOfTailCall(Arg)){
              ....
+        } else {
+          Source=Arg;
+        }

I prefer this:

           SDOperand Source = Arg;
           if (IsPossiblyOverriddenArgumentOfTailCall(Arg)) {
             ...
           }
6.
      if (!MemOpChains2.empty())
        Chain = DAG.getNode(ISD::TokenFactor, MVT::Other,
-                          &MemOpChains2[0], MemOpChains.size());
+                          &MemOpChains2[0], MemOpChains2.size());

This looks like a bug fix? Please check this part in first.

Thanks!

Evan


On Jan 8, 2008, at 5:04 AM, Arnold Schwaighofer wrote:

> Here is a patch to improve argument lowering for tail calls. Before
> this patch all outgoing arguments were move to the stack slot where
> they would go on a normal function call and from there moved back to
> the tail call stack slot to prevent overwriting of values.
> After this patch only arguments that source from callers arguments
> (formal_arguments) are lowered this way.
>
> I moved some code that would otherwise be duplicated to a new
> function 'GetMemCpyWithFlags'.
>
> Okay to commit?
>
> regards arnold
>
>
> <tailcall-
> improvement.patch>_______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev