opt_lut: new pass, to combine LUTs for tighter packing.

tests/opt/.gitignore

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+*.log

tests/opt/ice40_carry.v

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+module SB_CARRY (output CO, input I0, I1, CI);
+    assign CO = (I0 && I1) || ((I0 || I1) && CI);
+endmodule

tests/opt/opt_lut.v

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+module top(
+    input [8:0] a,
+    input [8:0] b,
+    output [8:0] o1,
+    output [2:0] o2,
+    input [2:0] c,
+    input [2:0] d,
+    output [2:0] o3,
+    output [2:0] o4,
+    input s
+);
+
+assign o1 = (s ? 0 : a + b);
+assign o2 = (s ? a : a - b);
+assign o3 = (s ? 4'b1111 : d + c);
+assign o4 = (s ? d : c - d);
+
+endmodule

tests/opt/opt_lut.ys

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+read_verilog opt_lut.v
+synth_ice40
+ice40_unlut
+design -save preopt
+
+opt_lut
+design -stash postopt
+
+design -copy-from preopt -as preopt top
+design -copy-from postopt -as postopt top
+equiv_make preopt postopt equiv
+techmap -map ice40_carry.v
+prep -flatten -top equiv
+equiv_induct
+equiv_status -assert

tests/opt/run-test.sh

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+#!/bin/bash
+set -e
+for x in *.ys; do
+  echo "Running $x.."
+  ../../yosys -ql ${x%.ys}.log $x
+done