[Bug tree-optimization/120074] [15/16 regression] ICE on valid code at -O1 with "-fno-tree-copy-prop -fno-tree-forwprop -fno-tree-ccp" on x86_64-linux-gnu: in decompose, at wide-int.h:1049

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120074

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Created attachment 61278
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=61278&action=edit
gimple testcase

Compile with -O1 -fgimple.

The reason for the special flags before is because

  _5 = _4 & 3;
  if (_5 < 0)

is always false.

I am not 100% sure this will happen ever without the special flags.

-fno-tree-ccp is needed because it does bitwise range info and (a&3) well
unsets the sign bit.

-fno-tree-forwprop  is needed because `non-negative<0` is matched.

-fno-tree-copy-prop is similar to -fno-tree-forwprop. Uses fold which then does
the backtrace to see non-negativeness.