[PATCH IRA] update_equiv_regs fails to set EQUIV reg-note for pseudo with more than one definition

[Felix Yang]

Hi,

    I find that update_equiv_regs in ira.c sets the wrong EQUIV
reg-note for pseudo with more than one definiton in certain situation.
    Here is a simplified RTL snippet after this function finishs handling:

 (insn 77 37 78 2 (set (reg:SI 171)
         (const_int 0 [0])) ticket151.c:33 52 {movsi_internal_dsp}
      (expr_list:REG_EQUAL (const_int 0 [0])
         (nil)))

......

(insn 79 50 53 2 (set (mem/c:SI (reg/f:SI 136) [2 g_728+0 S4 A64])
         (reg:SI 171)) ticket151.c:33 52 {movsi_internal_dsp}
      (expr_list:REG_DEAD (reg:SI 171)
         (nil)))
(insn 53 79 54 2 (set (mem/c:SI (reg/f:SI 162) [4 g_163+0 S4 A32])
         (reg:SI 163)) 52 {movsi_internal_dsp}
      (expr_list:REG_DEAD (reg:SI 163)
         (expr_list:REG_DEAD (reg/f:SI 162)
             (nil))))
(insn 54 53 14 2 (set (reg:SI 171)
         (mem/u/c:SI (symbol_ref/u:SI ("*.LC8") [flags 0x2]) [4  S4
A32])) ticket151.c:49 52 {movsi_internal_dsp}
      (expr_list:REG_EQUIV (mem/u/c:SI (symbol_ref/u:SI ("*.LC8")
[flags 0x2]) [4  S4 A32])
         (expr_list:REG_EQUAL (mem/u/c:SI (symbol_ref/u:SI ("*.LC8")
[flags 0x2]) [4  S4 A32])
             (nil))))


    The REG_EQUIV of insn 54 is not correct as pseudo 171 is defined
in insn 77 with a differerent value.
    This may causes reload replacing pseudo 171 with mem/u/c:SI
(symbol_ref/u:SI ("*.LC8"), which is wrong.
    A proposed patch for this issue, please comment:

 Index: gcc/ira.c
===================================================================
--- gcc/ira.c    (revision 215460)
+++ gcc/ira.c    (working copy)
@@ -3477,18 +3477,26 @@ update_equiv_regs (void)
           no_equiv (dest, set, NULL);
           continue;
         }
+
       /* Record this insn as initializing this register.  */
       reg_equiv[regno].init_insns
         = gen_rtx_INSN_LIST (VOIDmode, insn, reg_equiv[regno].init_insns);

       /* If this register is known to be equal to a constant, record that
          it is always equivalent to the constant.  */
-      if (DF_REG_DEF_COUNT (regno) == 1
-          && note && ! rtx_varies_p (XEXP (note, 0), 0))
+      if (note && ! rtx_varies_p (XEXP (note, 0), 0))
         {
-          rtx note_value = XEXP (note, 0);
-          remove_note (insn, note);
-          set_unique_reg_note (insn, REG_EQUIV, note_value);
+          if (DF_REG_DEF_COUNT (regno) == 1)
+        {
+          rtx note_value = XEXP (note, 0);
+          remove_note (insn, note);
+          set_unique_reg_note (insn, REG_EQUIV, note_value);
+        }
+          else
+        {
+              no_equiv (dest, set, NULL);
+              continue;
+        }
         }

       /* If this insn introduces a "constant" register, decrease the priority


Cheers,
Felix