[Bug tree-optimization/14799] [tree-ssa] convert a sequence of "if"s to a "switch" statement

[Bug tree-optimization/14799] [tree-ssa] convert a sequence of "if"s to a "switch" statement

[tom at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14799

Tom de Vries <tom at codesourcery dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tom at codesourcery dot com

--- Comment #3 from Tom de Vries <tom at codesourcery dot com> 2011-01-14 15:45:56 UTC ---
The example from the description field looks like this at tree level (optimized
dump with 4.5.1). It takes until late in the rtl untill the duplicate call
blocks are collapsed.
...
foo (int a)
{
<bb 2>:
  if (a_1(D) == 30)
    goto <bb 3>;
  else
    goto <bb 4>;

<bb 3>:
  bar (); [tail call]
  goto <bb 10>;

<bb 4>:
  if (a_1(D) == 31)
    goto <bb 5>;
  else
    goto <bb 6>;

<bb 5>:
  bar (); [tail call]
  goto <bb 10>;

<bb 6>:
  if (a_1(D) == 53)
    goto <bb 7>;
  else
    goto <bb 8>;

<bb 7>:
  bar (); [tail call]
  goto <bb 10>;

<bb 8>:
  if (a_1(D) == 23)
    goto <bb 9>;
  else
    goto <bb 10>;

<bb 9>:
  bar (); [tail call]

<bb 10>:
  return;
}
...

If the duplicate blocks would have been collapsed, it would look like this:
...
foo (int a)
{
<bb 2>:
  if (a_1(D) == 30)
    goto <bb 9>;
  else
    goto <bb 4>;

<bb 4>:
  if (a_1(D) == 31)
    goto <bb 9>;
  else
    goto <bb 6>;

<bb 6>:
  if (a_1(D) == 53)
    goto <bb 9>;
  else
    goto <bb 8>;

<bb 8>:
  if (a_1(D) == 23)
    goto <bb 9>;
  else
    goto <bb 10>;

<bb 9>:
  bar (); [tail call]

<bb 10>:
  return;
}
...
for this representation, the patch from PR 46935 comment 5 should work.

[Bug tree-optimization/14799] [tree-ssa] convert a sequence of "if"s to a "switch" statement

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=14799

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Martin Liska <marxin@gcc.gnu.org>:

https://gcc.gnu.org/g:03eb09292ef228d1d12b5168cdd748583b1f992a

commit r11-5605-g03eb09292ef228d1d12b5168cdd748583b1f992a
Author: Martin Liska <mliska@suse.cz>
Date:   Fri Aug 28 10:26:13 2020 +0200

    Add if-chain to switch conversion pass.

    gcc/ChangeLog:

            PR tree-optimization/14799
            PR ipa/88702
            * Makefile.in: Add gimple-if-to-switch.o.
            * dbgcnt.def (DEBUG_COUNTER): Add new debug counter.
            * passes.def: Include new pass_if_to_switch pass.
            * timevar.def (TV_TREE_IF_TO_SWITCH): New timevar.
            * tree-pass.h (make_pass_if_to_switch): New.
            * tree-ssa-reassoc.c (struct operand_entry): Move to the header.
            (dump_range_entry): Move to header file.
            (debug_range_entry): Likewise.
            (no_side_effect_bb): Make it global.
            * tree-switch-conversion.h (simple_cluster::simple_cluster):
            Add inline for couple of functions in order to prevent error
            about multiple defined symbols.
            * gimple-if-to-switch.cc: New file.
            * tree-ssa-reassoc.h: New file.

    gcc/testsuite/ChangeLog:

            PR tree-optimization/14799
            PR ipa/88702
            * gcc.dg/tree-ssa/pr96480.c: Disable if-to-switch conversion.
            * gcc.dg/tree-ssa/reassoc-32.c: Likewise.
            * g++.dg/tree-ssa/if-to-switch-1.C: New test.
            * gcc.dg/tree-ssa/if-to-switch-1.c: New test.
            * gcc.dg/tree-ssa/if-to-switch-2.c: New test.
            * gcc.dg/tree-ssa/if-to-switch-3.c: New test.
            * gcc.dg/tree-ssa/if-to-switch-4.c: New test.
            * gcc.dg/tree-ssa/if-to-switch-5.c: New test.
            * gcc.dg/tree-ssa/if-to-switch-6.c: New test.
            * gcc.dg/tree-ssa/if-to-switch-7.c: New test.
            * gcc.dg/tree-ssa/if-to-switch-8.c: New test.

[Bug tree-optimization/14799] [tree-ssa] convert a sequence of "if"s to a "switch" statement

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=14799

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #8 from Martin Liška <marxin at gcc dot gnu.org> ---
Implemented in master.

[Bug optimization/14799] New: [tree-ssa] convert a sequence of "if"s to a "switch" statement

[kazu at cs dot umass dot edu]

void bar (void);

void
foo (int a)
{
  if (a == 30)
    bar ();
  else if (a == 31)
    bar ();
  else if (a == 53)
    bar ();
  else if (a == 23)
    bar ();
}

The idea comes from LLVM.
Of course we should do this only if switch statements are expanded in
an (almost?) optimal way.

-- 
           Summary: [tree-ssa] convert a sequence of "if"s to a "switch"
                    statement
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Keywords: pessimizes-code
          Severity: enhancement
          Priority: P2
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at cs dot umass dot edu
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14799

[Bug tree-optimization/14799] [tree-ssa] convert a sequence of "if"s to a "switch" statement

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.5.0                       |---


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14799