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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/94516] [10 Regression] gnutls test ./psk-file
 fails since r10-7515-g2c0fa3ecf70d199af18785702e9e0548fd3ab793
Date: Tue, 07 Apr 2020 15:13:53 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94516

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
For the optimization issue, we could have a hack like:
--- gcc/postreload.c.jj 2020-04-07 16:54:23.638924247 +0200
+++ gcc/postreload.c    2020-04-07 17:06:44.055964581 +0200
@@ -328,6 +328,17 @@ reload_cse_simplify_set (rtx set, rtx_in
       else
        continue;

+      /* Prefer stack pointer adjustment over copies from a register
+        that happens to hold the right value already (unless it is
+        much higher cost), because in the sp +=3D const case the
+        pass_stack_adjustments pass can merge it with other stack
+        adjustments.  */
+      if (SET_DEST (set) =3D=3D stack_pointer_rtx
+         && GET_CODE (SET_SRC (set)) =3D=3D PLUS
+         && XEXP (SET_SRC (set), 0) =3D=3D stack_pointer_rtx
+         && CONST_INT_P (XEXP (SET_SRC (set), 1)))
+       this_cost *=3D 4;
+
       /* If equal costs, prefer registers over anything else.  That
         tends to lead to smaller instructions on some machines.  */
       if (this_cost < old_cost

Dunno... :(
Or do such a change only if there are no following sp adjustments that coul=
d be
combined with it (e.g. remember we've done such a change, and when we proce=
ss
next stack pointer adjustment with no sp uses in between or what exactly csa
does, and don't manage to optimize that one into sp =3D reg, try to undo the
previous change.=