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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ipa/105917] New: Missed passthru jump function
Date: Fri, 10 Jun 2022 12:14:49 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105917

            Bug ID: 105917
           Summary: Missed passthru jump function
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hubicka at gcc dot gnu.org
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

In this testcase:
struct a {int a;};
struct b {int b; struct a a;};

__attribute__ ((noinline))
static int
reta (struct a a)
{
        return a.a;
}
__attribute__ ((noinline))
static int=20
retba (struct b b)
{
  struct a *a =3D &b.a;
  return reta(*a);
}
int
main()
{
  struct b b =3D {1, {0}};
  return retba (b);
}

There is aggregat passthru from retba to reta but we get:

  _2 =3D reta (MEM[(struct a *)&b + 4B]);

Analyzing function: retba/1
  function  retba/1 parameter descriptors:
    param #0 b used undescribed_use
  Jump functions of caller  retba/1:
    callsite  retba/1 -> reta/0 :
       param 0: UNKNOWN
         Unknown bits
         Unknown VR

I constructed this to check dubious check for MEM_REF requiring offset to b=
e 0.
However surprisingly we miss the following too:

struct a {int a;};
struct b {int b; struct a a;};

__attribute__ ((noinline))
static int
reta (struct a a)
{
        return a.a;
}
__attribute__ ((noinline))
static int=20
retba (struct b b)
{
  //struct a *a =3D &b.a;
  //return reta(*a);
  return reta (b.a);
}
int
main()
{
  struct b b =3D {1, {0}};
  return retba (b);
}

  Jump functions of caller  retba/1:
    callsite  retba/1 -> reta/0 :
       param 0: UNKNOWN
         Unknown bits
         Unknown VR

I wonder which cases actually works :)=