opt_vps improvements for VPS read

tests/silimate/opt_vps.ys

@@ -157,3 +157,85 @@ select -assert-count 1 t:$dff
 design -reset
 log -pop
 
+# =============================================================================
+# Test 7: SAT equivalence — VPS read vs right-shift reference
+# Proves opt_vps produces a logically equivalent circuit to a hand-written
+# right-shift for a 256-bit register with 32-bit read window.
+# =============================================================================
+log -header "SAT equivalence: VPS read vs right-shift ref"
+log -push
+design -reset
+verific -cfg veri_optimize_wide_selector 1
+verific -cfg db_infer_wide_muxes_post_elaboration 0
+
+read -sv opt_vps_read.sv
+verific -import opt_vps_read
+proc; opt_clean
+opt_vps; opt_clean
+rename opt_vps_read gate
+
+read -sv opt_vps_read_ref.sv
+verific -import opt_vps_read
+proc; opt_clean
+rename opt_vps_read gold
+
+miter -equiv -flatten -make_assert gold gate miter
+hierarchy -top miter
+proc; opt; memory; opt
+clk2fflogic
+sat -set-init-zero -tempinduct -prove-asserts -verify
+design -reset
+log -pop
+
+# =============================================================================
+# Test 8: SAT self-equivalence — VPS read before vs after opt_vps
+# Proves opt_vps does not change the functional behavior for VPS reads.
+# =============================================================================
+log -header "SAT self-equivalence: VPS read before vs after opt_vps"
+log -push
+design -reset
+verific -cfg veri_optimize_wide_selector 1
+verific -cfg db_infer_wide_muxes_post_elaboration 0
+
+read -sv opt_vps_read.sv
+verific -import opt_vps_read
+proc; opt_clean
+rename opt_vps_read gold
+
+read -sv opt_vps_read.sv
+verific -import opt_vps_read
+proc; opt_clean
+opt_vps; opt_clean
+rename opt_vps_read gate
+
+miter -equiv -flatten -make_assert gold gate miter
+hierarchy -top miter
+proc; opt; memory; opt
+clk2fflogic
+sat -set-init-zero -tempinduct -prove-asserts -verify
+design -reset
+log -pop
+
+# =============================================================================
+# Test 9: Cell count verification — VPS read
+# After opt_vps, the $pmux should be replaced with a $shr.
+# =============================================================================
+log -header "Cell counts: VPS read post-opt_vps"
+log -push
+design -reset
+verific -cfg veri_optimize_wide_selector 1
+verific -cfg db_infer_wide_muxes_post_elaboration 0
+
+read -sv opt_vps_read.sv
+verific -import opt_vps_read
+proc; opt_clean
+opt_vps; opt_clean
+
+select -assert-none t:$pmux
+select -assert-count 1 t:$shr
+select -assert-count 1 t:$dff
+select -assert-count 1 t:$mux
+design -reset
+log -pop
+
+

tests/silimate/opt_vps_read.sv

@@ -0,0 +1,17 @@
+// Minimal variable-part-select (VPS) read: extracts a 32-bit word
+// from a 256-bit register at a dynamic byte offset.
+module opt_vps_read (
+    input  logic        clk,
+    input  logic        wr_en,
+    input  logic [7:0]  index,
+    input  logic [255:0] wdata,
+    output logic [31:0]  q
+);
+    logic [255:0] reg_data;
+
+    always_ff @(posedge clk)
+        if (wr_en)
+            reg_data <= wdata;
+
+    assign q = reg_data[index +: 32];
+endmodule

tests/silimate/opt_vps_read_ref.sv

@@ -0,0 +1,16 @@
+// Reference for VPS read: uses right-shift instead of variable part-select.
+module opt_vps_read (
+    input  logic        clk,
+    input  logic        wr_en,
+    input  logic [7:0]  index,
+    input  logic [255:0] wdata,
+    output logic [31:0]  q
+);
+    logic [255:0] reg_data;
+
+    always_ff @(posedge clk)
+        if (wr_en)
+            reg_data <= wdata;
+
+    assign q = (reg_data >> index);
+endmodule