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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/102121] New: switch conversion to load table
 should do integer compression
Date: Sun, 29 Aug 2021 20:43:26 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: missed-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102121

            Bug ID: 102121
           Summary: switch conversion to load table should do integer
                    compression
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
int f(int a)
{
switch (a)
{
    case 0:
      return 100;
    case 1:
      return 200;
    case 3:
      return 250;
    case 4:
      return 0;
    case 5:
      return 7;
    case 6:
      return 3;
}
return 0;
}

int f1(int a)
{
unsigned char t =3D 0;
switch (a)
{
    case 0:
      t=3D100;
      break;
    case 1:
      t =3D 200u;
      break;
    case 3:
      t =3D 250u;
      break;
    case 4:
      t =3D 0;
      break;
    case 5:
      t =3D 7;
      break;
    case 6:
      t =3D 3;
      break;
}
asm("":"+r"(t));
return t;
}

These two functions should have the same assembly and the load table should=
 be
using byte loads for both.=