https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83855
Segher Boessenkool <segher at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
CC| |segher at gcc dot gnu.org
Resolution|--- |INVALID
--- Comment #3 from Segher Boessenkool <segher at gcc dot gnu.org> ---
The internals manual explains this:
Note that @code{match_dup} should not be used to tell the compiler that
a particular register is being used for two operands (example:
@code{add} that adds one register to another; the second register is
both an input operand and the output operand). Use a matching
constraint (@pxref{Simple Constraints}) for those. @code{match_dup} is for the
cases where one
operand is used in two places in the template, such as an instruction
that computes both a quotient and a remainder, where the opcode takes
two input operands but the RTL template has to refer to each of those
twice; once for the quotient pattern and once for the remainder pattern.
