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shifter sign generation logic optimize

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This commit is contained in:
Kevin Kim 2023-03-07 10:57:06 -08:00
parent 81198ce6f6
commit 833e7bd2af
2 changed files with 19 additions and 11 deletions
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18
src/ieu/alu.sv
View File

@ -48,7 +48,7 @@ module alu #(parameter WIDTH=32) (
logic [WIDTH-1:0] MaskB; // BitMask of B
logic [WIDTH-1:0] CondMaskB; // Result of B mask select mux
logic [WIDTH-1:0] CondShiftA; // Result of A shifted select mux
logic [WIDTH-1:0] CondZextA; // Result of Zero Extend A select mux
logic [WIDTH-1:0] CondExtA; // Result of Zero Extend A select mux
logic [WIDTH-1:0] RevA; // Bit-reversed A
logic Carry, Neg; // Flags: carry out, negative
logic LT, LTU; // Less than, Less than unsigned
@ -56,7 +56,7 @@ module alu #(parameter WIDTH=32) (
logic SubArith; // Performing subtraction or arithmetic right shift
logic ALUOp; // 0 for address generation addition or 1 for regular ALU ops
logic Asign, Bsign; // Sign bits of A, B
logic [WIDTH:0] shA; // XLEN+1 bit input source to shifter
logic shSignA;
logic [WIDTH-1:0] rotA; // XLEN bit input source to shifter
logic [1:0] shASelect; // select signal for shifter source generation mux
logic Rotate; // Indicates if it is Rotate instruction
@ -80,7 +80,7 @@ module alu #(parameter WIDTH=32) (
assign CondMaskB = (Mask) ? MaskB : B;
end else assign CondMaskB = B;
// Sign/Zero extend mux
/*// Sign/Zero extend mux
if (WIDTH == 64) begin // rv64 must handle word s/z extensions
always_comb
case (shASelect)
@ -90,6 +90,14 @@ module alu #(parameter WIDTH=32) (
2'b11: shA = {{33{A[31]}}, A[31:0]}; //sign extend-word (sraw)
endcase
end else assign shA = (SubArith) ? {A[31], A} : {{1'b0},A}; // rv32 does need to handle s/z extensions
*/
if (WIDTH == 64) begin
mux3 #(1) signmux(A[63], A[31], 1'b0, {~SubArith, W64}, shSignA);
mux3 #(64) extendmux({{32{1'b0}}, A[31:0]},{{32{A[31]}}, A[31:0]}, A,{~W64, SubArith}, CondExtA);
end else begin
mux2 #(1) signmux(1'b0, A[31], SubArith, shSignA);
assign CondExtA = A;
end
// shifter rotate source select mux
if (`ZBB_SUPPORTED) begin
@ -99,7 +107,7 @@ module alu #(parameter WIDTH=32) (
if (`ZBA_SUPPORTED) begin: zbamuxes
// Pre-Shift
assign CondShiftA = shA[WIDTH-1:0] << (PreShiftAmt);
assign CondShiftA = CondExtA << (PreShiftAmt);
end else assign CondShiftA = A;
// Addition
@ -108,7 +116,7 @@ module alu #(parameter WIDTH=32) (
assign {Carry, Sum} = CondShiftA + CondInvB + {{(WIDTH-1){1'b0}}, SubArith};
// Shifts (configurable for rotation)
shifter sh(.shA(shA), .rotA(rotA), .Amt(B[`LOG_XLEN-1:0]), .Right(Funct3[2]), .W64(W64), .Y(Shift), .Rotate(Rotate));
shifter sh(.shA(CondExtA), .Sign(shSignA), .rotA(rotA), .Amt(B[`LOG_XLEN-1:0]), .Right(Funct3[2]), .W64(W64), .Y(Shift), .Rotate(Rotate));
// Condition code flags are based on subtraction output Sum = A-B.
// Overflow occurs when the numbers being subtracted have the opposite sign

12
src/ieu/shifter.sv
View File

@ -30,10 +30,10 @@
`include "wally-config.vh"
module shifter (
input logic [`XLEN:0] shA, // shift Source
input logic [`XLEN-1:0] shA, // shift Source
input logic [`XLEN-1:0] rotA, // rotate source
input logic [`LOG_XLEN-1:0] Amt, // Shift amount
input logic Right, Rotate, W64, // Shift right, rotate signals
input logic Right, Rotate, W64, Sign, // Shift right, rotate signals
output logic [`XLEN-1:0] Y); // Shifted result
logic [2*`XLEN-2:0] z, zshift; // Input to funnel shifter, shifted amount before truncated to 32 or 64 bits
@ -45,7 +45,7 @@ module shifter (
case({Right, Rotate})
2'b00: z = {shA[31:0], 31'b0};
2'b01: z = {rotA,rotA[31:1]};
2'b10: z = {{31{shA[32]}}, shA[31:0]};
2'b10: z = {{31{Sign}}, shA[31:0]};
2'b11: z = {rotA[30:0],rotA};
endcase
assign amttrunc = Amt; // shift amount
@ -54,7 +54,7 @@ module shifter (
case ({Right, Rotate})
2'b00: z = {shA[63:0],{63'b0}};
2'b01: z = {rotA, rotA[63:1]};
2'b10: z = {{63{shA[64]}},shA[63:0]};
2'b10: z = {{63{Sign}},shA[63:0]};
2'b11: z = {rotA[62:0],rotA[63:0]};
endcase
assign amttrunc = W64 ? {1'b0, Amt[4:0]} : Amt; // 32- or 64-bit shift
@ -62,12 +62,12 @@ module shifter (
end else begin: norotfunnel
if (`XLEN==32) begin:shifter // RV32
always_comb // funnel mux
if (Right) z = {{31{shA[32]}}, shA[31:0]};
if (Right) z = {{31{Sign}}, shA[31:0]};
else z = {shA[31:0], 31'b0};
assign amttrunc = Amt; // shift amount
end else begin:shifter // RV64
always_comb // funnel mux
if (Right) z = {{63{shA[64]}},shA[63:0]};
if (Right) z = {{63{Sign}},shA[63:0]};
else z = {shA[63:0],{63'b0}};
assign amttrunc = W64 ? {1'b0, Amt[4:0]} : Amt; // 32- or 64-bit shift
end