[PATCH v3] xtensa: Prepare the transition from Reload to LRA

[Takayuki 'January June' Suwa <jjsuwa_sys3175@yahoo.co.jp>]

On 2022/10/18 21:16, Max Filippov wrote:
> Hi Suwa-san,
Hi!

> I've noticed that this is related to the following hunk:
> 
> -#define CALL_USED_REGISTERS                                            \
> +#define CALL_REALLY_USED_REGISTERS                                     \
>  {                                                                      \
> -  1, 1, 4, 4, 4, 4, 4, 4, 1, 1, 1, 1, 2, 2, 2, 2,                      \
> -  1, 1, 1,                                                             \
> +  0, 0, 4, 4, 4, 4, 4, 4, 1, 1, 1, 1, 2, 2, 2, 2,                      \
> +  0, 0, 1,                                                             \
>    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,                      \
>    1,                                                                   \
>  }
> 
> And the following change on top of v2 fixes this regression for me:
> 
> diff --git a/gcc/config/xtensa/xtensa.h b/gcc/config/xtensa/xtensa.h
> index 6b60e5960625..897f87f735da 100644
> --- a/gcc/config/xtensa/xtensa.h
> +++ b/gcc/config/xtensa/xtensa.h
> @@ -244,7 +244,7 @@ along with GCC; see the file COPYING3.  If not see
> 
> #define CALL_REALLY_USED_REGISTERS                                     \
> {                                                                      \
> -  0, 0, 4, 4, 4, 4, 4, 4, 1, 1, 1, 1, 2, 2, 2, 2,                      \
> +  1, 0, 4, 4, 4, 4, 4, 4, 1, 1, 1, 1, 2, 2, 2, 2,                      \
>   0, 0, 1,                                                             \
>   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,                      \
>   1,                                                                   \

If we take "CALL_REALLY_USED_REGISTERS" literally, it makes sense because the CALL0/CALLX0 instructions actually change the A0 register.
(little question: Then FIXED_REGISTERS is interpreted as not including the link register, but is that correct...)

===
This patch provides the first step in the transition from Reload to LRA
in Xtensa.

gcc/ChangeLog:

	* config/xtensa/xtensa-proto.h
	(xtensa_split1_finished_p, xtensa_split_DI_reg_imm): New prototypes.
	* config/xtensa/xtensa.cc
	(xtensa_split1_finished_p, xtensa_split_DI_reg_imm, xtensa_lra_p):
	New functions.
	(TARGET_LRA_P): Replace the dummy hook with xtensa_lra_p.
	(xt_true_regnum): Rework.
	* gcc/config/xtensa/xtensa.h (CALL_REALLY_USED_REGISTERS):
	Switch from CALL_USED_REGISTERS, and revise the comment.
	* gcc/config/xtensa/constraints.md (Y):
	Use !xtensa_split1_finished_p() instead of can_create_pseudo_p().
	* gcc/config/xtensa/predicates.md (move_operand): Ditto.
	* gcc/config/xtensa/xtensa.md: Add two new split patterns:
	  - splits DImode immediate load into two SImode ones
	  - puts out-of-constraint SImode constants into the constant pool
	* gcc/config/xtensa/xtensa.opt (-mlra): New target-specific option
	for testing purpose.
---
 gcc/config/xtensa/constraints.md  |  2 +-
 gcc/config/xtensa/predicates.md   |  2 +-
 gcc/config/xtensa/xtensa-protos.h |  2 +
 gcc/config/xtensa/xtensa.cc       | 69 ++++++++++++++++++++++++++-----
 gcc/config/xtensa/xtensa.h        |  8 ++--
 gcc/config/xtensa/xtensa.md       | 36 ++++++++++++----
 gcc/config/xtensa/xtensa.opt      |  4 ++
 7 files changed, 99 insertions(+), 24 deletions(-)

diff --git a/gcc/config/xtensa/constraints.md b/gcc/config/xtensa/constraints.md
index e4c314b267c..cd200d6d15a 100644
--- a/gcc/config/xtensa/constraints.md
+++ b/gcc/config/xtensa/constraints.md
@@ -121,7 +121,7 @@
  (ior (and (match_code "const_int,const_double,const,symbol_ref,label_ref")
 	   (match_test "TARGET_AUTO_LITPOOLS"))
       (and (match_code "const_int")
-	   (match_test "can_create_pseudo_p ()"))))
+	   (match_test "! xtensa_split1_finished_p ()"))))
 
 ;; Memory constraints.  Do not use define_memory_constraint here.  Doing so
 ;; causes reload to force some constants into the constant pool, but since
diff --git a/gcc/config/xtensa/predicates.md b/gcc/config/xtensa/predicates.md
index 0590c0f81a9..c11e8634dbe 100644
--- a/gcc/config/xtensa/predicates.md
+++ b/gcc/config/xtensa/predicates.md
@@ -149,7 +149,7 @@
      (ior (and (match_code "const_int")
 	       (match_test "(GET_MODE_CLASS (mode) == MODE_INT
 			     && xtensa_simm12b (INTVAL (op)))
-			    || can_create_pseudo_p ()"))
+			    || ! xtensa_split1_finished_p ()"))
 	  (and (match_code "const_int,const_double,const,symbol_ref,label_ref")
 	       (match_test "(TARGET_CONST16 || TARGET_AUTO_LITPOOLS)
 			    && CONSTANT_P (op)
diff --git a/gcc/config/xtensa/xtensa-protos.h b/gcc/config/xtensa/xtensa-protos.h
index 459e2aac9fc..bc75ad9698a 100644
--- a/gcc/config/xtensa/xtensa-protos.h
+++ b/gcc/config/xtensa/xtensa-protos.h
@@ -58,6 +58,8 @@ extern char *xtensa_emit_call (int, rtx *);
 extern char *xtensa_emit_sibcall (int, rtx *);
 extern bool xtensa_tls_referenced_p (rtx);
 extern enum rtx_code xtensa_shlrd_which_direction (rtx, rtx);
+extern bool xtensa_split1_finished_p (void);
+extern void xtensa_split_DI_reg_imm (rtx *);
 
 #ifdef TREE_CODE
 extern void init_cumulative_args (CUMULATIVE_ARGS *, int);
diff --git a/gcc/config/xtensa/xtensa.cc b/gcc/config/xtensa/xtensa.cc
index 828c7642b7c..950eb5a59be 100644
--- a/gcc/config/xtensa/xtensa.cc
+++ b/gcc/config/xtensa/xtensa.cc
@@ -56,6 +56,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "hw-doloop.h"
 #include "rtl-iter.h"
 #include "insn-attr.h"
+#include "tree-pass.h"
 
 /* This file should be included last.  */
 #include "target-def.h"
@@ -199,6 +200,7 @@ static void xtensa_output_mi_thunk (FILE *file, tree thunk ATTRIBUTE_UNUSED,
 				    HOST_WIDE_INT delta,
 				    HOST_WIDE_INT vcall_offset,
 				    tree function);
+static bool xtensa_lra_p (void);
 
 static rtx xtensa_delegitimize_address (rtx);
 
@@ -295,7 +297,7 @@ static rtx xtensa_delegitimize_address (rtx);
 #define TARGET_CANNOT_FORCE_CONST_MEM xtensa_cannot_force_const_mem
 
 #undef TARGET_LRA_P
-#define TARGET_LRA_P hook_bool_void_false
+#define TARGET_LRA_P xtensa_lra_p
 
 #undef TARGET_LEGITIMATE_ADDRESS_P
 #define TARGET_LEGITIMATE_ADDRESS_P	xtensa_legitimate_address_p
@@ -492,21 +494,30 @@ xtensa_mask_immediate (HOST_WIDE_INT v)
 int
 xt_true_regnum (rtx x)
 {
-  if (GET_CODE (x) == REG)
+  if (REG_P (x))
     {
-      if (reg_renumber
-	  && REGNO (x) >= FIRST_PSEUDO_REGISTER
-	  && reg_renumber[REGNO (x)] >= 0)
+      if (! HARD_REGISTER_P (x)
+	  && reg_renumber
+	  && (lra_in_progress || reg_renumber[REGNO (x)] >= 0))
 	return reg_renumber[REGNO (x)];
       return REGNO (x);
     }
-  if (GET_CODE (x) == SUBREG)
+  if (SUBREG_P (x))
     {
       int base = xt_true_regnum (SUBREG_REG (x));
-      if (base >= 0 && base < FIRST_PSEUDO_REGISTER)
-        return base + subreg_regno_offset (REGNO (SUBREG_REG (x)),
-                                           GET_MODE (SUBREG_REG (x)),
-                                           SUBREG_BYTE (x), GET_MODE (x));
+
+      if (base >= 0
+	  && HARD_REGISTER_NUM_P (base))
+	{
+	  struct subreg_info info;
+
+	  subreg_get_info (lra_in_progress
+			   ? (unsigned) base : REGNO (SUBREG_REG (x)),
+			   GET_MODE (SUBREG_REG (x)),
+			   SUBREG_BYTE (x), GET_MODE (x), &info);
+	  if (info.representable_p)
+	    return base + info.offset;
+	}
     }
   return -1;
 }
@@ -2477,6 +2488,36 @@ xtensa_shlrd_which_direction (rtx op0, rtx op1)
 }
 
 
+/* Return true after "split1" pass has been finished.  */
+
+bool
+xtensa_split1_finished_p (void)
+{
+  return cfun && (cfun->curr_properties & PROP_rtl_split_insns);
+}
+
+
+/* Split a DImode pair of reg (operand[0]) and const_int (operand[1]) into
+   two SImode pairs, the low-part (operands[0] and [1]) and the high-part
+   (operands[2] and [3]).  */
+
+void
+xtensa_split_DI_reg_imm (rtx *operands)
+{
+  rtx lowpart, highpart;
+
+  if (WORDS_BIG_ENDIAN)
+    split_double (operands[1], &highpart, &lowpart);
+  else
+    split_double (operands[1], &lowpart, &highpart);
+
+  operands[3] = highpart;
+  operands[2] = gen_highpart (SImode, operands[0]);
+  operands[1] = lowpart;
+  operands[0] = gen_lowpart (SImode, operands[0]);
+}
+
+
 /* Implement TARGET_CANNOT_FORCE_CONST_MEM.  */
 
 static bool
@@ -5119,4 +5160,12 @@ xtensa_delegitimize_address (rtx op)
   return op;
 }
 
+/* Implement TARGET_LRA_P.  */
+
+static bool
+xtensa_lra_p (void)
+{
+  return TARGET_LRA;
+}
+
 #include "gt-xtensa.h"
diff --git a/gcc/config/xtensa/xtensa.h b/gcc/config/xtensa/xtensa.h
index 16e3d55e896..2275fe6d426 100644
--- a/gcc/config/xtensa/xtensa.h
+++ b/gcc/config/xtensa/xtensa.h
@@ -229,7 +229,7 @@ along with GCC; see the file COPYING3.  If not see
 }
 
 /* 1 for registers not available across function calls.
-   These must include the FIXED_REGISTERS and also any
+   These need not include the FIXED_REGISTERS but must any
    registers that can be used without being saved.
    The latter must include the registers where values are returned
    and the register where structure-value addresses are passed.
@@ -242,10 +242,10 @@ along with GCC; see the file COPYING3.  If not see
 
    Proper values are computed in TARGET_CONDITIONAL_REGISTER_USAGE.  */
 
-#define CALL_USED_REGISTERS						\
+#define CALL_REALLY_USED_REGISTERS					\
 {									\
-  1, 1, 4, 4, 4, 4, 4, 4, 1, 1, 1, 1, 2, 2, 2, 2,			\
-  1, 1, 1,								\
+  1, 0, 4, 4, 4, 4, 4, 4, 1, 1, 1, 1, 2, 2, 2, 2,			\
+  0, 0, 1,								\
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,			\
   1,									\
 }
diff --git a/gcc/config/xtensa/xtensa.md b/gcc/config/xtensa/xtensa.md
index 608110c20bc..2e7f76ada5c 100644
--- a/gcc/config/xtensa/xtensa.md
+++ b/gcc/config/xtensa/xtensa.md
@@ -940,14 +940,9 @@
 	 because of offering further optimization opportunities.  */
       if (register_operand (operands[0], DImode))
 	{
-	  rtx lowpart, highpart;
-
-	  if (TARGET_BIG_ENDIAN)
-	    split_double (operands[1], &highpart, &lowpart);
-	  else
-	    split_double (operands[1], &lowpart, &highpart);
-	  emit_insn (gen_movsi (gen_lowpart (SImode, operands[0]), lowpart));
-	  emit_insn (gen_movsi (gen_highpart (SImode, operands[0]), highpart));
+	  xtensa_split_DI_reg_imm (operands);
+	  emit_move_insn (operands[0], operands[1]);
+	  emit_move_insn (operands[2], operands[3]);
 	  DONE;
 	}
 
@@ -981,6 +976,19 @@
     }
 })
 
+(define_split
+  [(set (match_operand:DI 0 "register_operand")
+	(match_operand:DI 1 "const_int_operand"))]
+  "!TARGET_CONST16 && !TARGET_AUTO_LITPOOLS
+   && ! xtensa_split1_finished_p ()"
+  [(set (match_dup 0)
+	(match_dup 1))
+   (set (match_dup 2)
+	(match_dup 3))]
+{
+  xtensa_split_DI_reg_imm (operands);
+})
+
 ;; 32-bit Integer moves
 
 (define_expand "movsi"
@@ -1017,6 +1025,18 @@
    (set_attr "mode"	"SI")
    (set_attr "length"	"2,2,2,2,2,2,3,3,3,3,6,3,3,3,3,3")])
 
+(define_split
+  [(set (match_operand:SI 0 "register_operand")
+	(match_operand:SI 1 "const_int_operand"))]
+  "!TARGET_CONST16 && !TARGET_AUTO_LITPOOLS
+   && ! xtensa_split1_finished_p ()
+   && ! xtensa_simm12b (INTVAL (operands[1]))"
+  [(set (match_dup 0)
+	(match_dup 1))]
+{
+  operands[1] = force_const_mem (SImode, operands[1]);
+})
+
 (define_split
   [(set (match_operand:SI 0 "register_operand")
 	(match_operand:SI 1 "constantpool_operand"))]
diff --git a/gcc/config/xtensa/xtensa.opt b/gcc/config/xtensa/xtensa.opt
index 08338e39060..00d2db4eae1 100644
--- a/gcc/config/xtensa/xtensa.opt
+++ b/gcc/config/xtensa/xtensa.opt
@@ -34,6 +34,10 @@ mextra-l32r-costs=
 Target RejectNegative Joined UInteger Var(xtensa_extra_l32r_costs) Init(0)
 Set extra memory access cost for L32R instruction, in clock-cycle units.
 
+mlra
+Target Mask(LRA)
+Use LRA instead of reload (transitional).
+
 mtarget-align
 Target
 Automatically align branch targets to reduce branch penalties.
-- 
2.30.2