[Bug tree-optimization/97997] Missed optimization: Multiply of extended integer cannot overflow

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97997

Andrew Pinski  changed:

   What|Removed |Added

   Target Milestone|--- |11.0
   Keywords||missed-optimization
   Severity|normal  |enhancement

[Bug tree-optimization/97997] Missed optimization: Multiply of extended integer cannot overflow

[matthijs at stdin dot nl via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97997

--- Comment #5 from Matthijs Kooijman  ---
Awesome, thanks for the quick response and fix!

[Bug tree-optimization/97997] Missed optimization: Multiply of extended integer cannot overflow

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97997

Jakub Jelinek  changed:

   What|Removed |Added

 Resolution|--- |FIXED
 Status|ASSIGNED|RESOLVED

--- Comment #4 from Jakub Jelinek  ---
Fixed for 11.1+.

[Bug tree-optimization/97997] Missed optimization: Multiply of extended integer cannot overflow

[cvs-commit at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97997

--- Comment #3 from CVS Commits  ---
The master branch has been updated by Jakub Jelinek :

https://gcc.gnu.org/g:a3ebc13492ff238873f2c6a7a3e51abefec1d052

commit r11-5444-ga3ebc13492ff238873f2c6a7a3e51abefec1d052
Author: Jakub Jelinek 
Date:   Thu Nov 26 16:24:07 2020 +0100

match.pd: Use ranges to optimize some x * y / y to x [PR97997]

For signed integers with undefined overflow we already optimize x * y / y
into x, but for signed integers with -fwrapv or unsigned integers we don't.
The following patch allows optimizing that into just x if value ranges
prove that x * y will never overflow.
It uses the global SSA_NAME_RANGE_INFO only, because like mentioned
in another PR we don't currently have a way to tell the ranger from
match.pd
the use stmt (and we'd need in that case to tell ranger to only follow
SSA_NAME_DEF_STMTs + SSA_NAME_RANGE_INFO and never go in the other
direction, as following immediate uses seems forbidden in match.pd).
Another possibility would be to optimize this during vrp, but on the
other side the optimization itself is match.pd-ish.

2020-11-26  Jakub Jelinek  

PR tree-optimization/97997
* match.pd ((t * 2) / 2) -> t): Optimize even for defined
overflow if ranges prove there is no overflow.

* gcc.dg/tree-ssa/pr97997-1.c: New test.
* gcc.dg/tree-ssa/pr97997-2.c: New test.

[Bug tree-optimization/97997] Missed optimization: Multiply of extended integer cannot overflow

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97997

Jakub Jelinek  changed:

   What|Removed |Added

   Assignee|unassigned at gcc dot gnu.org  |jakub at gcc dot gnu.org
 Ever confirmed|0   |1
 Status|UNCONFIRMED |ASSIGNED
   Last reconfirmed||2020-11-25

--- Comment #2 from Jakub Jelinek  ---
Created attachment 49629
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49629=edit
gcc11-pr97997.patch

Untested fix.

[Bug tree-optimization/97997] Missed optimization: Multiply of extended integer cannot overflow

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97997

Jakub Jelinek  changed:

   What|Removed |Added

 CC||jakub at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek  ---
unsigned short
f1 (unsigned short x)
{
  return x * 10 / 10;
}

unsigned short
f2 (unsigned short x)
{
  int a = x;
  int b = 10;
  int c = 10;
  return a * b / c;
}

unsigned short
f3 (unsigned short x)
{
  return x * 10U / 10;
}

unsigned short
f4 (unsigned short x)
{
  unsigned a = x;
  unsigned b = 10;
  unsigned c = 10;
  return a * b / c;
}

For f1 we fold it already during generic folding, f2 we fold during ccp using
the
/* Simplify (t * 2) / 2) -> t.  */
(for div (trunc_div ceil_div floor_div round_div exact_div)
 (simplify
  (div (mult:c @0 @1) @1)
  (if (ANY_INTEGRAL_TYPE_P (type)
   && TYPE_OVERFLOW_UNDEFINED (type))
   @0)))
rule.