Type Conversion Error in Synopsys Design Compiler During Elaboration

[HenryChenFLC]

I have been trying to set up synthesis with the RTL code available and ran into some elaboration errors in Design Compiler.
We are hoping to get some support for the errors.

Error: /projects/mockingbird/wa/henrychen/syn_n12_OMI_1/RTL/omi_asic_device_reference_design/tlx/tl/cb_tlxr_mac.vhdl:3263: Conversion function on formal port is not supported. (ELAB-285)
Error: /projects/mockingbird/wa/henrychen/syn_n12_OMI_1/RTL/omi_asic_device_reference_design/tlx/tl/cb_tlxt_mac.vhdl:1155: Conversion function on formal port is not supported. (ELAB-285)

These appear to be related to the Tconv that comes from the ibm lib:
USE ibm.std_ulogic_support.all; -- Tconv

There is an attribute that seems relevant:

ATTRIBUTE synthesis_return OF result:VARIABLE IS "FEED_THROUGH" ;

I tried adding to it with something that might get recognized by Design Compiler:

-- synopsys built_in SYN_FEED_THRU;
ATTRIBUTE synthesis_return OF result:VARIABLE IS "FEED_THROUGH"

but this still results in the same conversion not supported error.