Re: Repost: RFA [4.1]: improvement to if-conversion and cross-jumping (PR20070)

[Ian Lance Taylor <ian at airs dot com>]

Joern RENNECKE <joern.rennecke@st.com> writes:

> +/* Check if *XP is equivalent to Y.  Until an an unreconcilable difference is
> +   found, use in-group changes with validate_change on *XP to make register
> +   assignments agree.  It is the (not necessarily direct) callers
> +   responsibility to verify / confirm / cancel these changes, as appropriate.
> +   RVALUE indicates if the processed piece of rtl is used as a destination, in
> +   which case we can't have different registers being an input.  Returns
> +   nonzero if the two blocks have been identified as equivalent, zero otherwise.
> +   RVALUE == 0: destination
> +   RVALUE == 1: source
> +   RVALUE == -1: source, ignore SET_DEST of SET / clobber.  */
> +bool
> +rtx_equiv_p (rtx *xp, rtx y, int rvalue, struct equiv_info *info)

I think that it's very unwise to have a function named rtx_equiv_p
which makes changes to its operands.  The "_p" suffix implies that the
function is a predicate.  Predicates should never change their
operands.  The name rtx_equiv_p strongly suggests a function which
tests whether two rtx variables are equivalent.  That is not what this
function does.

I also find the comment to be somewhat unclear; what does it mean "to
make register assignments agree?"

Ian