Improve EmitAsmStmt() to
- Not tie physregs with the "+r" constraint, but instead add the hard register as an input constraint. This makes "+r" and "=r":"r" look the same in the output.
Background: Macro intensive code may contain inline assembly statements with multiple operands constrained to the same physreg. Such a case with the operand constraints "+r" : "r" currently triggers the TwoAddressInstructionPass assertion against any extra use of a tied register. Furthermore, TwoAddress will insert a COPY to that physreg even though isel has already done so (for the non-tied use), which may lead to a second redundant instruction currently.
A simple fix for this is to not emit tied physreg uses in the first place for the "+r" constraint, which is what this patch does.
- Give an error on multiple outputs to the same physical register.
This should be reported and this is also what GCC does.