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From: "jskumari at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/109009] Shrink Wrap missed opportunity
Date: Sun, 05 Mar 2023 05:23:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109009

--- Comment #2 from Surya Kumari Jangala <jskumari at gcc dot gnu.org> ---
For the working testcase:

long
foo (long i, long cond)
{
  if (cond)
    bar ();
  return i;
}

The input RTL to the shrink wrap pass is:

BB2:
   set r100, compare(r4, 0)
   if r100 jump BB4 else jump BB3

BB3:
   set mem(r1+32), r3
   call bar()
   set r3, mem(r1+32)

BB4:
   return r3

The shrink wrap pass concludes that only BB3 requires a prolog and successf=
ully
does shrink wrapping.

For the non-working case:
long
foo (long i, long cond)
{
  if (cond)
    bar ();
  return i+1;
}

The input rtl to the shrink wrap pass is:

BB2:
   set r100, compare(r4, 0)
   set r31, r3
   if r100 jump BB4 else jump BB3

BB3:
   call bar()

BB4:
   set r3, r31+1
   return r3

The shrink wrap pass decides that both BB2 and BB3 require a prolog, and
finally the prolog is placed in BB2. Thus shrink wrapping fails for this te=
st.=