[llvm-commits] [llvm] r50075 - in /llvm/trunk: lib/Target/X86/README-X86-64.txt lib/Target/X86/X86ISelLowering.cpp lib/Target/X86/X86MachineFunctionInfo.h test/CodeGen/X86/x86-64-sret-return.ll

[Duncan Sands]

Hi Dan,

> +A better implementation would be to relax the LLVM IR rules for sret
> +arguments to allow a function with an sret argument to have a non-void
> +return type, and to have the front-end to set up the sret argument value
> +as the return value of the function. The front-end could more easily
> +emit uses of the returned struct value to be in terms of the function's
> +lowered return value, and it would free non-C frontends from a
> +complication only required by a C-based ABI.

there is already some support for this in llvm-gcc, i.e. having a function
return the "shadow" pointer.  In llvm-abi.h (note the bit about RetPtr):

  /// HandleAggregateShadowArgument - This callback is invoked if the function
  /// returns an aggregate value by using a "shadow" first parameter, which is
  /// a pointer to the aggregate, of type PtrArgTy.  If RetPtr is set to true,
  /// the pointer argument itself is returned from the function.
  void HandleAggregateShadowArgument(const PointerType *PtrArgTy, bool RetPtr){}

Ciao,

Duncan.