[Bug tree-optimization/122608] `(a ? CST0 : CST1) OP CST3` is not optimized (for gimple COND)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122608

--- Comment #4 from Jeffrey A. Law <law at gcc dot gnu.org> ---
Given the code looks like this:

  b_2 = a_1(D) > 0; 
  t_3 = b_2 ? 10 : 20;
  t_4 = t_3 + 20;

ISTM that we could have a match.pd pattern which optimizes into the b ? 30 : 40
form.  Essentially given X op C where X comes from a COND_EXPR where the
true/false arms are constants we can compute trueval op C and falseval op C and
use thoes results in the COND_EXPR.