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[rtl/alu] Remove unused comparison operations

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These operations (ALU_GT, ALU_GTU, ALU_LE, ALU_LEU) are remnants of
of the original OpenRISC design. RISC-V does not have these instructions
and instead implements the operations by reversing operands for ALU_LT,
ALU_LTU, ALU_GE, ALU_GEU.

This resolves lowRISC/ibex#420 reported by @udinator.
This commit is contained in:
Pirmin Vogel 2019-10-24 15:06:25 +01:00
parent 294849bb18
commit 0331ed61b1
3 changed files with 11 additions and 29 deletions
Download patch file Download diff file Expand all files Collapse all files

2
lint/verilator_waiver.vlt
View file

@ -28,7 +28,7 @@ lint_off -msg UNUSED -file "*/rtl/ibex_if_stage.sv" -lines 80
// Bits of signal are not used: shift_right_result_ext[32]
// cleaner to write all bits even if not all are used
lint_off -msg UNUSED -file "*/rtl/ibex_alu.sv" -lines 107
lint_off -msg UNUSED -file "*/rtl/ibex_alu.sv" -lines 105
// Bits of signal are not used: alu_adder_ext_i[0]
// Bottom bit is round, not needed

34
rtl/ibex_alu.sv
View file

@ -50,10 +50,8 @@ module ibex_alu (
// Comparator OPs
ALU_EQ, ALU_NE,
ALU_GTU, ALU_GEU,
ALU_LTU, ALU_LEU,
ALU_GT, ALU_GE,
ALU_LT, ALU_LE,
ALU_GE, ALU_GEU,
ALU_LT, ALU_LTU,
ALU_SLT, ALU_SLTU,
ALU_SLET, ALU_SLETU: adder_op_b_negate = 1'b1;
@ -128,10 +126,8 @@ module ibex_alu (
cmp_signed = 1'b0;
unique case (operator_i)
ALU_GT,
ALU_GE,
ALU_LT,
ALU_LE,
ALU_SLT,
ALU_SLET: begin
cmp_signed = 1'b1;
@ -144,7 +140,6 @@ module ibex_alu (
assign is_equal = (adder_result == 32'b0);
assign is_equal_result_o = is_equal;
// Is greater equal
always_comb begin
if ((operand_a_i[31] ^ operand_b_i[31]) == 1'b0) begin
@ -166,8 +161,6 @@ module ibex_alu (
// (a[31] == 1 && b[31] == 0) => 0
// (a[31] == 0 && b[31] == 1) => 1
// generate comparison result
logic cmp_result;
@ -175,15 +168,12 @@ module ibex_alu (
cmp_result = is_equal;
unique case (operator_i)
ALU_EQ: cmp_result = is_equal;
ALU_NE: cmp_result = ~is_equal;
ALU_GT, ALU_GTU: cmp_result = is_greater_equal & ~is_equal;
ALU_GE, ALU_GEU: cmp_result = is_greater_equal;
ALU_LT, ALU_SLT,
ALU_LTU, ALU_SLTU: cmp_result = ~is_greater_equal;
ALU_SLET,
ALU_SLETU,
ALU_LE, ALU_LEU: cmp_result = ~is_greater_equal | is_equal;
ALU_EQ: cmp_result = is_equal;
ALU_NE: cmp_result = ~is_equal;
ALU_GE, ALU_GEU: cmp_result = is_greater_equal;
ALU_LT, ALU_LTU,
ALU_SLT, ALU_SLTU: cmp_result = ~is_greater_equal;
ALU_SLET, ALU_SLETU: cmp_result = ~is_greater_equal | is_equal;
default:;
endcase
@ -191,8 +181,6 @@ module ibex_alu (
assign comparison_result_o = cmp_result;
////////////////
// Result mux //
////////////////
@ -215,10 +203,8 @@ module ibex_alu (
// Comparison Operations
ALU_EQ, ALU_NE,
ALU_GTU, ALU_GEU,
ALU_LTU, ALU_LEU,
ALU_GT, ALU_GE,
ALU_LT, ALU_LE,
ALU_GE, ALU_GEU,
ALU_LT, ALU_LTU,
ALU_SLT, ALU_SLTU,
ALU_SLET, ALU_SLETU: result_o = {31'h0,cmp_result};

4
rtl/ibex_pkg.sv
View file

@ -50,10 +50,6 @@ typedef enum logic [4:0] {
// Comparisons
ALU_LT,
ALU_LTU,
ALU_LE,
ALU_LEU,
ALU_GT,
ALU_GTU,
ALU_GE,
ALU_GEU,
ALU_EQ,