[Bug tree-optimization/31178] VRP can infer a range for b in a >> b and a << b

[vincent-gcc at vinc17 dot net via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=31178

--- Comment #17 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
(In reply to Richard Biener from comment #16)
> Note for shifts the precision of the shift operand does not have to match
> that of the shifted operand.  In your case you have vector << scalar, so you
> definitely want to look at scalars precision when deriving a range for
> scalar, _not_ at element_precision of vector (or the LHS)!

I'm not sure I understand what you mean, but the C standard says:

  The integer promotions are performed on each of the operands. The type
  of the result is that of the promoted left operand. If the value of the
  right operand is negative or is greater than or equal to the width of
  the promoted left operand, the behavior is undefined.

So, what matters is the type of the promoted *left* operand (corresponding to
vector above).