Re: [PATCH V5] Use reg mode to move sub blocks for parameters and returns

[Jeff Law <jeffreyalaw@gmail.com>]

On 3/16/23 21:39, Jiufu Guo wrote:
> Hi,
> 
> When assigning a parameter to a variable, or assigning a variable to
> return value with struct type, and the parameter/return is passed
> through registers.
> For this kind of case, it would be better to use the nature mode of
> the registers to move the content for the assignment.
> 
> As the example code (like code in PR65421):
> 
> typedef struct SA {double a[3];} A;
> A ret_arg_pt (A *a) {return *a;} // on ppc64le, expect only 3 lfd(s)
> A ret_arg (A a) {return a;} // just empty fun body
> void st_arg (A a, A *p) {*p = a;} //only 3 stfd(s)
> 
> Comparing with previous version:
> https://gcc.gnu.org/pipermail/gcc-patches/2023-January/609394.html
> This version refine code to eliminated reductant code in  the sub
> routine "move_sub_blocks".
> 
> Bootstrap and regtest pass on ppc64{,le}.
> Is this ok for trunk?
> 
> BR,
> Jeff (Jiufu)
> 
> 	PR target/65421
> 
> gcc/ChangeLog:
> 
> 	* cfgexpand.cc (expand_used_vars): Update to mark DECL_USEDBY_RETURN_P
> 	for returns.
> 	* expr.cc (move_sub_blocks): New function.
> 	(expand_assignment): Update assignment code about returns/parameters.
> 	* function.cc (assign_parm_setup_block): Update to mark
> 	DECL_REGS_TO_STACK_P for parameter.
> 	* tree-core.h (struct tree_decl_common): Add comment.
> 	* tree.h (DECL_USEDBY_RETURN_P): New define.
> 	(DECL_REGS_TO_STACK_P): New define.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.target/powerpc/pr65421-1.c: New test.
> 	* gcc.target/powerpc/pr65421.c: New test.
> 
> ---
>   gcc/cfgexpand.cc                             | 14 +++++
>   gcc/expr.cc                                  | 61 ++++++++++++++++++++
>   gcc/function.cc                              |  3 +
>   gcc/tree-core.h                              |  4 +-
>   gcc/tree.h                                   |  9 +++
>   gcc/testsuite/gcc.target/powerpc/pr65421-1.c |  6 ++
>   gcc/testsuite/gcc.target/powerpc/pr65421.c   | 33 +++++++++++
>   7 files changed, 129 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/gcc.target/powerpc/pr65421-1.c
>   create mode 100644 gcc/testsuite/gcc.target/powerpc/pr65421.c
> 
> diff --git a/gcc/expr.cc b/gcc/expr.cc
> index 15be1c8db99..97a7be9542e 100644
> --- a/gcc/expr.cc
> +++ b/gcc/expr.cc
> @@ -5559,6 +5559,41 @@ mem_ref_refers_to_non_mem_p (tree ref)
>     return non_mem_decl_p (base);
>   }
>   
> +/* Sub routine of expand_assignment, invoked when assigning from a
> +   parameter or assigning to a return val on struct type which may
> +   be passed through registers.  The mode of register is used to
> +   move the content for the assignment.
> +
> +   This routine generates code for expression FROM which is BLKmode,
> +   and move the generated content to TO_RTX by su-blocks in SUB_MODE.  */
> +
> +static void
> +move_sub_blocks (rtx to_rtx, tree from, machine_mode sub_mode)
> +{
> +  gcc_assert (MEM_P (to_rtx));
> +
> +  HOST_WIDE_INT size = MEM_SIZE (to_rtx).to_constant ();
Consider the case of a BLKmode return value.  Isn't TO_RTX in this case 
a BLKmode object?

It looks pretty good at this point.

jeff