combine: Special case set_noop_p in two spots

Here is the incremental patch I was talking about.
For noop sets, we don't need to test much, they can go to i2
unless that would violate i3 JUMP condition.

With this the try_combine on the pr119291.c testcase doesn't fail,
but succeeds and we get
(insn 22 21 23 4 (set (pc)
        (pc)) "pr119291.c":27:15 2147483647 {NOOP_MOVE}
     (nil))
(insn 23 22 24 4 (set (reg/v:SI 117 [ e ])
        (reg/v:SI 116 [ e ])) 96 {*movsi_internal}
     (expr_list:REG_DEAD (reg/v:SI 116 [ e ])
        (nil)))
(note 24 23 25 4 NOTE_INSN_DELETED)
(insn 25 24 26 4 (set (reg/v:SI 116 [ e ])
        (const_int 0 [0])) "pr119291.c":28:13 96 {*movsi_internal}
     (nil))
(note 26 25 27 4 NOTE_INSN_DELETED)
(insn 27 26 28 4 (set (reg:DI 128 [ _9 ])
        (const_int 0 [0])) "pr119291.c":28:13 95 {*movdi_internal}
     (nil))
after it.

2025-05-01  Jakub Jelinek  <jakub@redhat.com>

	* combine.cc (try_combine): Sets which satisfy set_noop_p can go
	to i2 unless i3 is a jump and the other set is not.

diff --git a/gcc/combine.cc b/gcc/combine.cc
index 873c2bdd469886b9daf8c82cb1458e84fb27b5a6..67cf0447607f6ed0cc4e0aa19525e9fc069bf1e2 100644 (file)
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -4020,34 +4020,34 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
         in i3, so we need to make sure that we won't wrongly hoist a SET
         to i2 that would conflict with a death note present in there, or
         would have its dest modified or used between i2 and i3.  */
-      if (!modified_between_p (SET_SRC (set1), i2, i3)
-         && !(REG_P (SET_DEST (set1))
-              && find_reg_note (i2, REG_DEAD, SET_DEST (set1)))
-         && !(GET_CODE (SET_DEST (set1)) == SUBREG
-              && find_reg_note (i2, REG_DEAD,
-                                SUBREG_REG (SET_DEST (set1))))
-         && SET_DEST (set1) != pc_rtx
-         && !reg_used_between_p (SET_DEST (set1), i2, i3)
+      if ((set_noop_p (set1)
+          || (!modified_between_p (SET_SRC (set1), i2, i3)
+              && !(REG_P (SET_DEST (set1))
+                   && find_reg_note (i2, REG_DEAD, SET_DEST (set1)))
+              && !(GET_CODE (SET_DEST (set1)) == SUBREG
+                   && find_reg_note (i2, REG_DEAD,
+                                     SUBREG_REG (SET_DEST (set1))))
+              && SET_DEST (set1) != pc_rtx
+              && !reg_used_between_p (SET_DEST (set1), i2, i3)))
          /* If I3 is a jump, ensure that set0 is a jump so that
             we do not create invalid RTL.  */
-         && (!JUMP_P (i3) || SET_DEST (set0) == pc_rtx)
-        )
+         && (!JUMP_P (i3) || SET_DEST (set0) == pc_rtx))
        {
          newi2pat = set1;
          newpat = set0;
        }
-      else if (!modified_between_p (SET_SRC (set0), i2, i3)
-              && !(REG_P (SET_DEST (set0))
-                   && find_reg_note (i2, REG_DEAD, SET_DEST (set0)))
-              && !(GET_CODE (SET_DEST (set0)) == SUBREG
-                   && find_reg_note (i2, REG_DEAD,
-                                     SUBREG_REG (SET_DEST (set0))))
-              && SET_DEST (set0) != pc_rtx
-              && !reg_used_between_p (SET_DEST (set0), i2, i3)
+      else if ((set_noop_p (set0)
+               || (!modified_between_p (SET_SRC (set0), i2, i3)
+                   && !(REG_P (SET_DEST (set0))
+                        && find_reg_note (i2, REG_DEAD, SET_DEST (set0)))
+                   && !(GET_CODE (SET_DEST (set0)) == SUBREG
+                        && find_reg_note (i2, REG_DEAD,
+                                          SUBREG_REG (SET_DEST (set0))))
+                   && SET_DEST (set0) != pc_rtx
+                   && !reg_used_between_p (SET_DEST (set0), i2, i3)))
               /* If I3 is a jump, ensure that set1 is a jump so that
                  we do not create invalid RTL.  */
-              && (!JUMP_P (i3) || SET_DEST (set1) == pc_rtx)
-             )
+              && (!JUMP_P (i3) || SET_DEST (set1) == pc_rtx))
        {
          newi2pat = set0;
          newpat = set1;