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

[Jiufu Guo <guojiufu@linux.ibm.com>]

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/cfgexpand.cc b/gcc/cfgexpand.cc
index 1a1b26b1c6c..eda4d85d140 100644
--- a/gcc/cfgexpand.cc
+++ b/gcc/cfgexpand.cc
@@ -2158,6 +2158,20 @@ expand_used_vars (bitmap forced_stack_vars)
     frame_phase = off ? align - off : 0;
   }
 
+  /* Collect VARs on returns.  */
+  if (DECL_RESULT (current_function_decl))
+    {
+      edge_iterator ei;
+      edge e;
+      FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR_FOR_FN (cfun)->preds)
+	if (greturn *ret = safe_dyn_cast<greturn *> (last_stmt (e->src)))
+	  {
+	    tree val = gimple_return_retval (ret);
+	    if (val && VAR_P (val))
+	      DECL_USEDBY_RETURN_P (val) = 1;
+	  }
+    }
+
   /* Set TREE_USED on all variables in the local_decls.  */
   FOR_EACH_LOCAL_DECL (cfun, i, var)
     TREE_USED (var) = 1;
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 ();
+  HOST_WIDE_INT sub_size = GET_MODE_SIZE (sub_mode).to_constant ();
+  HOST_WIDE_INT len = size / sub_size;
+  gcc_assert (size % sub_size == 0);
+
+  push_temp_slots ();
+
+  rtx from_rtx = expand_expr (from, NULL_RTX, GET_MODE (to_rtx), EXPAND_NORMAL);
+  for (int i = 0; i < len; i++)
+    {
+      rtx temp = gen_reg_rtx (sub_mode);
+      rtx src = adjust_address (from_rtx, sub_mode, sub_size * i);
+      rtx dest = adjust_address (to_rtx, sub_mode, sub_size * i);
+      emit_move_insn (temp, src);
+      emit_move_insn (dest, temp);
+    }
+
+  preserve_temp_slots (to_rtx);
+  pop_temp_slots ();
+  return;
+}
+
 /* Expand an assignment that stores the value of FROM into TO.  If NONTEMPORAL
    is true, try generating a nontemporal store.  */
 
@@ -6045,6 +6080,32 @@ expand_assignment (tree to, tree from, bool nontemporal)
       return;
     }
 
+  /* If it is assigning from a struct param which may be passed via registers,
+     it would be better to use the register's mode to move sub-blocks for the
+     assignment.  */
+  if (TREE_CODE (from) == PARM_DECL && mode == BLKmode
+      && DECL_REGS_TO_STACK_P (from))
+    {
+      rtx parm = DECL_INCOMING_RTL (from);
+      machine_mode sub_mode
+	= REG_P (parm) ? word_mode : GET_MODE (XEXP (XVECEXP (parm, 0, 0), 0));
+      move_sub_blocks (to_rtx, from, sub_mode);
+      return;
+    }
+
+  /* If it is assigning to a struct var which will be returned, and the
+     function is returning via registers, it would be better to use the
+     register's mode to move sub-blocks for the assignment.  */
+  if (VAR_P (to) && DECL_USEDBY_RETURN_P (to) && mode == BLKmode
+      && TREE_CODE (from) != CONSTRUCTOR
+      && GET_CODE (DECL_RTL (DECL_RESULT (current_function_decl))) == PARALLEL)
+    {
+      rtx ret = DECL_RTL (DECL_RESULT (current_function_decl));
+      machine_mode sub_mode = GET_MODE (XEXP (XVECEXP (ret, 0, 0), 0));
+      move_sub_blocks (to_rtx, from, sub_mode);
+      return;
+    }
+
   /* Compute FROM and store the value in the rtx we got.  */
 
   push_temp_slots ();
diff --git a/gcc/function.cc b/gcc/function.cc
index cfc4d2f74af..b8cd3d89d22 100644
--- a/gcc/function.cc
+++ b/gcc/function.cc
@@ -2991,6 +2991,9 @@ assign_parm_setup_block (struct assign_parm_data_all *all,
 
       mem = validize_mem (copy_rtx (stack_parm));
 
+      if (MEM_P (mem) && size != 0 && size % UNITS_PER_WORD == 0)
+	DECL_REGS_TO_STACK_P (parm) = 1;
+
       /* Handle values in multiple non-contiguous locations.  */
       if (GET_CODE (entry_parm) == PARALLEL && !MEM_P (mem))
 	emit_group_store (mem, entry_parm, data->arg.type, size);
diff --git a/gcc/tree-core.h b/gcc/tree-core.h
index fd2be57b78c..30656658431 100644
--- a/gcc/tree-core.h
+++ b/gcc/tree-core.h
@@ -1808,7 +1808,9 @@ struct GTY(()) tree_decl_common {
      In VAR_DECL, PARM_DECL and RESULT_DECL, this is
      DECL_HAS_VALUE_EXPR_P.  */
   unsigned decl_flag_2 : 1;
-  /* In FIELD_DECL, this is DECL_PADDING_P.  */
+  /* In FIELD_DECL, this is DECL_PADDING_P
+     In VAR_DECL, this is DECL_USEDBY_RETURN_P
+     In PARM_DECL, this is DECL_REGS_TO_STACK_P.  */
   unsigned decl_flag_3 : 1;
   /* Logically, these two would go in a theoretical base shared by var and
      parm decl. */
diff --git a/gcc/tree.h b/gcc/tree.h
index 91375f9652f..356c6067bac 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -3019,6 +3019,15 @@ extern void decl_value_expr_insert (tree, tree);
 #define DECL_PADDING_P(NODE) \
   (FIELD_DECL_CHECK (NODE)->decl_common.decl_flag_3)
 
+/* Used in a VAR_DECL to indicate that it is used by a return stmt.  */
+#define DECL_USEDBY_RETURN_P(NODE) \
+  (VAR_DECL_CHECK (NODE)->decl_common.decl_flag_3)
+
+/* Used in a PARM_DECL to indicate that it is struct parameter passed
+   by registers totally and stored to stack during setup.  */
+#define DECL_REGS_TO_STACK_P(NODE) \
+  (PARM_DECL_CHECK (NODE)->decl_common.decl_flag_3)
+
 /* Used in a FIELD_DECL to indicate whether this field is not a flexible
    array member. This is only valid for the last array type field of a
    structure.  */
diff --git a/gcc/testsuite/gcc.target/powerpc/pr65421-1.c b/gcc/testsuite/gcc.target/powerpc/pr65421-1.c
new file mode 100644
index 00000000000..4e1f87f7939
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr65421-1.c
@@ -0,0 +1,6 @@
+/* PR target/65421 */
+/* { dg-options "-O2" } */
+
+typedef struct LARGE {double a[4]; int arr[32];} LARGE;
+LARGE foo (LARGE a){return a;}
+/* { dg-final { scan-assembler-times {\mmemcpy\M} 1 } } */
diff --git a/gcc/testsuite/gcc.target/powerpc/pr65421.c b/gcc/testsuite/gcc.target/powerpc/pr65421.c
new file mode 100644
index 00000000000..fd5ad542c64
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr65421.c
@@ -0,0 +1,33 @@
+/* PR target/65421 */
+/* { dg-options "-O2" } */
+/* { dg-require-effective-target powerpc_elfv2 } */
+/* { dg-require-effective-target has_arch_ppc64 } */
+
+typedef struct FLOATS
+{
+  double a[3];
+} FLOATS;
+
+/* 3 lfd */
+FLOATS ret_arg_pt (FLOATS *a){return *a;}
+/* { dg-final { scan-assembler-times {\mlfd\M} 3 } } */
+
+/* 3 stfd */
+void st_arg (FLOATS a, FLOATS *p) {*p = a;}
+/* { dg-final { scan-assembler-times {\mstfd\M} 3 } } */
+
+/* blr */
+FLOATS ret_arg (FLOATS a) {return a;}
+
+typedef struct MIX
+{
+  double a[2];
+  long l;
+} MIX;
+
+/* std 3 param regs to return slot */
+MIX ret_arg1 (MIX a) {return a;}
+/* { dg-final { scan-assembler-times {\mstd\M} 3 } } */
+
+/* count insns */
+/* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 13 } } */
-- 
2.31.1