verilator/test_regress/t/t_dfg_synthesis.v

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Optimize complex combinational logic in DFG (#6298) This patch adds DfgLogic, which is a vertex that represents a whole, arbitrarily complex combinational AstAlways or AstAssignW in the DfgGraph. Implementing this requires computing the variables live at entry to the AstAlways (variables read by the block), so there is a new ControlFlowGraph data structure and a classical data-flow analysis based live variable analysis to do that at the variable level (as opposed to bit/element level). The actual CFG construction and live variable analysis is best effort, and might fail for currently unhandled constructs or data types. This can be extended later. V3DfgAstToDfg is changed to convert the Ast into an initial DfgGraph containing only DfgLogic, DfgVertexSplice and DfgVertexVar vertices. The DfgLogic are then subsequently synthesized into primitive operations by the new V3DfgSynthesize pass, which is a combination of the old V3DfgAstToDfg conversion and new code to handle AstAlways blocks with complex flow control. V3DfgSynthesize by default will synthesize roughly the same constructs as V3DfgAstToDfg used to handle before, plus any logic that is part of a combinational cycle within the DfgGraph. This enables breaking up these cycles, for which there are extensions to V3DfgBreakCycles in this patch as well. V3DfgSynthesize will then delete all non synthesized or non synthesizable DfgLogic vertices and the rest of the Dfg pipeline is identical, with minor changes to adjust for the changed representation. Because with this change we can now eliminate many more UNOPTFLAT, DFG has been disabled in all the tests that specifically target testing the scheduling and reporting of circular combinational logic.
2025-08-19 16:06:38 +02:00
// DESCRIPTION: Verilator: Verilog Test module
//
// This file ONLY is placed under the Creative Commons Public Domain, for
// any use, without warranty, 2025 by Geza Lore.
// SPDX-License-Identifier: CC0-1.0
`define signal(name, expr) wire [$bits(expr)-1:0] ``name = expr
module t (
`include "portlist.vh" // Boilerplate generated by t_dfg_break_cycles.py
rand_a, rand_b, srand_a, srand_b
);
`include "portdecl.vh" // Boilerplate generated by t_dfg_break_cycles.py
input rand_a;
input rand_b;
input srand_a;
input srand_b;
wire logic [63:0] rand_a;
wire logic [63:0] rand_b;
wire logic signed [63:0] srand_a;
wire logic signed [63:0] srand_b;
//////////////////////////////////////////////////////////////////////////
logic [2:0] simple;
always_comb begin
simple[0] = rand_a[0];
simple[1] = rand_a[1];
simple[2] = rand_a[2];
end
`signal(SIMPLE, simple);
logic [1:0] reassign;
always_comb begin
reassign[0] = rand_a[0];
reassign[0] = ~rand_a[0];
reassign[1] = rand_a[1];
reassign[1] = ~rand_a[1];
end
`signal(REASSIGN, reassign);
logic [1:0] use_intermediate_a;
logic [1:0] use_intermediate_b;
always_comb begin
use_intermediate_a[0] = rand_a[0];
use_intermediate_b[0] = ~use_intermediate_a[0];
use_intermediate_a[1] = rand_a[1];
use_intermediate_a[0] = ~rand_a[0];
use_intermediate_b[1] = ~use_intermediate_a[1];
use_intermediate_a[1] = ~rand_a[1];
end
`signal(USE_INTERMEDIATE, {use_intermediate_a, use_intermediate_b});
logic [2:0] self_circular;
always_comb begin
self_circular[0] = rand_a[0];
self_circular[1] = ~self_circular[0];
self_circular[2] = ~self_circular[1];
end
`signal(SELF_CIRCULAR, self_circular);
logic [2:0] part_circular;
always_comb begin
part_circular[0] = rand_a[0];
part_circular[1] = ~part_circular[0];
end
// part_circular[2] deliberately undriven!
`signal(PART_CIRCULAR, part_circular);
logic [3:0] split_circular;
always_comb begin
split_circular[0] = rand_a[0];
split_circular[2] = rand_a[1];
end
always_comb begin
split_circular[1] = ~split_circular[0];
split_circular[3] = ~split_circular[2];
end
`signal(SPLIT_CIRCULAR, split_circular);
logic [3:0] conditional_a;
always_comb begin
conditional_a = 4'd0;
if (rand_a[0]) begin
conditional_a = rand_b[3:0];
end else begin
conditional_a = ~rand_b[3:0];
end
end
`signal(CONDITONAL_A, conditional_a);
logic [3:0] conditional_b;
always_comb begin
conditional_b = 4'd0;
if (rand_a[0]) begin
conditional_b = rand_b[3:0];
end
end
`signal(CONDITONAL_B, conditional_b);
// verilator lint_off LATCH
logic [3:0] conditional_c;
always_comb begin // nosynth
if (rand_a[0]) begin
conditional_c = rand_b[3:0];
end
if (~rand_a[0]) begin
conditional_c = ~rand_b[3:0];
end
end
`signal(CONDITONAL_C, conditional_c);
// verilator lint_on LATCH
logic [3:0] conditional_d;
always_comb begin
if (rand_a[0]) begin
conditional_d = rand_b[3:0];
end else if (rand_a[1]) begin
conditional_d = ~rand_b[3:0];
end else begin
conditional_d = rand_b[7:4];
end
end
`signal(CONDITONAL_D, conditional_d);
logic [3:0] conditional_e;
always_comb begin
conditional_e = 4'd0;
if (rand_a[0]) begin
conditional_e = rand_b[3:0];
end else begin
if (rand_a[1]) begin
conditional_e = rand_b[3:0];
end else begin
conditional_e = rand_b[7:4];
end
conditional_e = ~conditional_e;
end
end
`signal(CONDITONAL_E, conditional_e);
logic condigional_f;
always_comb begin
if (rand_b[0]) begin
condigional_f = 1'h1;
if (rand_b[1]) begin
condigional_f = rand_a[0];
end
end else begin
condigional_f = 1'b0;
end
end
`signal(CONDITONAL_F, condigional_f);
logic [7:0] partial_conditional_a;
always_comb begin
partial_conditional_a[1:0] = 2'd0;
if (rand_a[0]) begin
partial_conditional_a[0] = rand_b[0];
end else begin
partial_conditional_a[1] = rand_b[1];
end
partial_conditional_a[4:3] = rand_b[4:3];
end
`signal(PARTIAL_CONDITONAL_A, partial_conditional_a);
logic [3:0] partial_conditional_b;
always_comb begin
partial_conditional_b[1:0] = 2'd0;
if (rand_a[0]) begin
partial_conditional_b[0] = rand_b[0];
end
if (rand_a[1]) begin
partial_conditional_b[1] = rand_b[1];
end
end
`signal(PARTIAL_CONDITONAL_B, partial_conditional_b);
logic [3:0] becomes_full;
always_comb begin
becomes_full[2:0] = rand_a[2:0];
becomes_full[3] = ~rand_a[3];
if (rand_b[0]) begin
becomes_full = ~becomes_full;
end
end
`signal(BECOMES_FULL, becomes_full);
// verilator lint_off LATCH
logic [3:0] latch_a;
logic [3:0] latch_b;
always_comb begin // nosynth
if (rand_b[0]) begin
latch_a[3:1] = ~rand_a[3:1];
end
latch_b = latch_a;
end
assign latch_a[0] = rand_a[0];
`signal(LATCH, latch_b);
// verilator lint_on LATCH
// verilator lint_off MULTIDRIVEN
logic static_temporary_a;
logic static_temporary_b;
logic static_temporary_tmp;
always_comb begin // revert
static_temporary_tmp = rand_a[0];
static_temporary_a = ~static_temporary_tmp;
end
always_comb begin // revert
static_temporary_tmp = static_temporary_a;
static_temporary_b = ~static_temporary_tmp;
end
// verilator lint_on MULTIDRIVEN
`signal(STATIC_TEMPORARY, {static_temporary_tmp, static_temporary_b, static_temporary_a, rand_a[0]});
logic [2:0] partial_temporary_a;
logic [2:0] partial_temporary_tmp;
always_comb begin
partial_temporary_tmp[2] = rand_a[3];
partial_temporary_tmp[1] = rand_a[2];
partial_temporary_tmp[0] = rand_a[1];
partial_temporary_a = partial_temporary_tmp;
end
`signal(PARTIAL_TEMPORARY, partial_temporary_a);
endmodule