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

[Jeff Law via Gcc-patches]

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