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From: "vmakarov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/102147] IRA dependent on 32-bit vs 64-bit
 pointer size
Date: Wed, 22 Sep 2021 18:11:23 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102147

--- Comment #7 from Vladimir Makarov <vmakarov at gcc dot gnu.org> ---
I've been thinking about ways to fix this problem but only come to the
following patch.  The patch results in working mostly the same for 64-bit
targets and different for 32-bit targets. In any case the profitability is =
only
an estimation so I think the patch is ok.  Avoiding 4 stage bootstrap is mo=
re
important than a bit slower RA on 32-bit targets (which is questionable) on=
 few
border cases.

I am going to commit the patch this Friday.

--- a/gcc/ira-build.c
+++ b/gcc/ira-build.c
@@ -629,7 +629,7 @@ ior_hard_reg_conflicts (ira_allocno_t a, const_hard_reg=
_set
set)
 bool
 ira_conflict_vector_profitable_p (ira_object_t obj, int num)
 {
-  int nw;
+  int nbytes;
   int max =3D OBJECT_MAX (obj);
   int min =3D OBJECT_MIN (obj);

@@ -638,9 +638,14 @@ ira_conflict_vector_profitable_p (ira_object_t obj, int
num)
        in allocation.  */
     return false;

-  nw =3D (max - min + IRA_INT_BITS) / IRA_INT_BITS;
-  return (2 * sizeof (ira_object_t) * (num + 1)
-         < 3 * nw * sizeof (IRA_INT_TYPE));
+  nbytes =3D (max - min) / 8 + 1;
+  STATIC_ASSERT (sizeof (ira_object_t) <=3D 8);
+  /* Don't use sizeof (ira_object_t), use constant 8.  Size of ira_object_=
t (a
+     pointer) is different on 32-bit and 64-bit targets.  Usage sizeof
+     (ira_object_t) can result in different code generation by GCC built as
32-
+     and 64-bit program.  In any case the profitability is just an estimat=
ion
+     and border cases are rare.  */
+  return (2 * 8 /* sizeof (ira_object_t) */ * (num + 1) < 3 * nbytes);
 }

 /* Allocates and initialize the conflict vector of OBJ for NUM=