LoongArch: Modify the address calculation logic for obtaining array element values through fp.

Modify address calculation logic from (((a x C) + fp) + offset) to ((fp + offset) + a x C).
Thereby modifying the register dependencies and optimizing the code.
The value of C is 2 4 or 8.

The following is the assembly code before and after a loop modification in spec2006 401.bzip:

                 old                      |                 new
 735 .L71:                                |  735 .L71:
 736         slli.d  $r12,$r15,2          |  736         slli.d  $r12,$r15,2
 737         ldx.w   $r13,$r22,$r12       |  737         ldx.w   $r13,$r22,$r12
 738         addi.d  $r15,$r15,-1         |  738         addi.d  $r15,$r15,-1
 739         slli.w  $r16,$r15,0          |  739         slli.w  $r16,$r15,0
 740         addi.w  $r13,$r13,-1         |  740         addi.w  $r13,$r13,-1
 741         slti    $r14,$r13,0          |  741         slti    $r14,$r13,0
 742         add.w   $r12,$r26,$r13       |  742         add.w   $r12,$r26,$r13
 743         maskeqz $r12,$r12,$r14       |  743         maskeqz $r12,$r12,$r14
 744         masknez $r14,$r13,$r14       |  744         masknez $r14,$r13,$r14
 745         or      $r12,$r12,$r14       |  745         or      $r12,$r12,$r14
 746         ldx.bu  $r14,$r30,$r12       |  746         ldx.bu  $r14,$r30,$r12
 747         lu12i.w $r13,4096>>12        |  747         alsl.d  $r14,$r14,$r18,2
 748         ori     $r13,$r13,432        |  748         ldptr.w $r13,$r14,0
 749         add.d   $r13,$r13,$r3        |  749         addi.w  $r17,$r13,-1
 750         alsl.d  $r14,$r14,$r13,2     |  750         stptr.w $r17,$r14,0
 751         ldptr.w $r13,$r14,-1968      |  751         slli.d  $r13,$r13,2
 752         addi.w  $r17,$r13,-1         |  752         stx.w   $r12,$r22,$r13
 753         st.w    $r17,$r14,-1968      |  753         ldptr.w $r12,$r19,0
 754         slli.d  $r13,$r13,2          |  754         blt     $r12,$r16,.L71
 755         stx.w   $r12,$r22,$r13       |  755         .align  4
 756         ldptr.w $r12,$r18,-2048      |  756
 757         blt     $r12,$r16,.L71       |  757
 758         .align  4                    |  758

This patch is ported from riscv's commit r14-3111.

gcc/ChangeLog:

	* config/loongarch/loongarch.cc (mem_shadd_or_shadd_rtx_p): New function.
	(loongarch_legitimize_address): Add logical transformation code.

1 files changed, 43 insertions, 0 deletions

diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
index b494040..b8f6f66 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -3219,6 +3219,22 @@ loongarch_split_symbol (rtx temp, rtx addr, machine_mode mode, rtx *low_out)
   return true;
 }
 
+/* Helper loongarch_legitimize_address.  Given X, return true if it
+   is a left shift by 1, 2 or 3 positions or a multiply by 2, 4 or 8.
+
+   This respectively represent canonical shift-add rtxs or scaled
+   memory addresses.  */
+static bool
+mem_shadd_or_shadd_rtx_p (rtx x)
+{
+  return ((GET_CODE (x) == ASHIFT
+	   || GET_CODE (x) == MULT)
+	  && CONST_INT_P (XEXP (x, 1))
+	  && ((GET_CODE (x) == ASHIFT && IN_RANGE (INTVAL (XEXP (x, 1)), 1, 3))
+	      || (GET_CODE (x) == MULT
+		  && IN_RANGE (exact_log2 (INTVAL (XEXP (x, 1))), 1, 3))));
+}
+
 /* This function is used to implement LEGITIMIZE_ADDRESS.  If X can
    be legitimized in a way that the generic machinery might not expect,
    return a new address, otherwise return NULL.  MODE is the mode of
@@ -3242,6 +3258,33 @@ loongarch_legitimize_address (rtx x, rtx oldx ATTRIBUTE_UNUSED,
   loongarch_split_plus (x, &base, &offset);
   if (offset != 0)
     {
+      /* Handle (plus (plus (mult (a) (mem_shadd_constant)) (fp)) (C)) case.  */
+      if (GET_CODE (base) == PLUS && mem_shadd_or_shadd_rtx_p (XEXP (base, 0))
+	  && IMM12_OPERAND (offset))
+	{
+	  rtx index = XEXP (base, 0);
+	  rtx fp = XEXP (base, 1);
+
+	  if (REG_P (fp) && REGNO (fp) == VIRTUAL_STACK_VARS_REGNUM)
+	    {
+	      /* If we were given a MULT, we must fix the constant
+		 as we're going to create the ASHIFT form.  */
+	      int shift_val = INTVAL (XEXP (index, 1));
+	      if (GET_CODE (index) == MULT)
+		shift_val = exact_log2 (shift_val);
+
+	      rtx reg1 = gen_reg_rtx (Pmode);
+	      rtx reg3 = gen_reg_rtx (Pmode);
+	      loongarch_emit_binary (PLUS, reg1, fp, GEN_INT (offset));
+	      loongarch_emit_binary (PLUS, reg3,
+				     gen_rtx_ASHIFT (Pmode, XEXP (index, 0),
+						     GEN_INT (shift_val)),
+				     reg1);
+
+	      return reg3;
+	    }
+	}
+
       if (!loongarch_valid_base_register_p (base, mode, false))
 	base = copy_to_mode_reg (Pmode, base);
       addr = loongarch_add_offset (NULL, base, offset);