This patch is a one line correction/clarification to GCC's current
RTL documentation that explains a USE of a MEM is permissible.

PR rtl-optimization/99930 is an interesting example on x86_64 where
the backend generates better code when a USE is a (const) MEM than
when it is a REG. In fact the backend relies on CSE to propagate the
MEM (a constant pool reference) into the USE, to enable combine to
merge/simplify instructions.

This change has been tested with a make bootstrap, but as it might
provoke a discussion, I've decided to not consider it "obvious".
Ok for mainline (to document the actual current behavior)?


2022-07-23  Roger Sayle   <roger@nextmovesoftware.com>

gcc/ChangeLog
        * doc/rtl.texi (use): Document that the operand may be a MEM.


Roger
--