I think multiplier inference is working in prjtrellis and yosys master

[minecraft2048]

Multipliers using manual instantiation of the MULT18X18D primitive. Inference and more advanced DSP features are not yet supported.

Reading at that I thought that inference is not working, but I tried this code:

module testmac(input clk, input [31:0] a, input [31:0] b, output [63:0] out);
    reg [63:0] acc;
    always @(posedge clk) begin
        acc <= a * b;
    end
    assign out = acc;
endmodule

and used yosys and got this:
2.52. Printing statistics.

=== testmac ===

   Number of wires:                 23
   Number of wire bits:            849
   Number of public wires:          23
   Number of public wire bits:     849
   Number of memories:               0
   Number of memory bits:            0
   Number of processes:              0
   Number of cells:                121
     CCU2C                          53
     MULT18X18D                      4
     TRELLIS_FF                     64

Looks like it can infer multipliers, I don't know whether its working or not though