[Bug tree-optimization/82854] more missing simplifcations

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82854

--- Comment #3 from Andrew Pinski  ---
(In reply to Andrew Pinski from comment #2)
> /* 0 - (x & 0x8000) -> x & 0x8000 */
> LLVM does

Actually RTL has done this since at least GCC 4.1.0, most likely before.

[Bug tree-optimization/82854] more missing simplifcations

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82854

Andrew Pinski  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
 Ever confirmed|0   |1
   Last reconfirmed||2021-08-07

--- Comment #2 from Andrew Pinski  ---
Summary of some of these
/* x + (x & 0x8000) -> x & 0x7fff */
No one does
/* (x | 0x8000) + 0x8000 -> x & 0x7FFF */
LLVM does
/* x & (0x7FFF - x) -> x & 0x8000 */
No one does, ICC does (-x + 0x7FFF) & x
/* x | (x + 0x8000) -> x | 0x8000 */
LLVM does
/* x | (0x7FFF - x) -> x | 0x7FFF */
No one does, ICC does (-x + 0x7FFF) | x

/* x | (x ^ y) -> x | y */
GCC and LLVM

/* -x | 0xFFFE -> x | 0xFFFE */
LLVM does
/* 0 - (x & 0x8000) -> x & 0x8000 */
LLVM does

/* ~(x + c) -> ~c - x */
GCC and LLVM
/* (x | c) - c -> x & ∼c */
GCC and LLVM

/* 0x7FFF - (x ^ c) -> x ^ (0x7FFF - c) */
LLVM does

[Bug tree-optimization/82854] more missing simplifcations

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82854

Andrew Pinski  changed:

   What|Removed |Added

   Keywords||missed-optimization
   Severity|normal  |enhancement

[Bug tree-optimization/82854] more missing simplifcations

[andi-gcc at firstfloor dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82854

--- Comment #1 from Andi Kleen  ---
Also I suppose a lot of them could be generalized to 8/16/64bit.