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Create module for instruction class prediction and decoding.

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This commit is contained in:
Ross Thompson 2023-02-26 20:20:30 -06:00
parent 86f611577f
commit 3804626166
3 changed files with 150 additions and 90 deletions
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28
src/ifu/bpred/RASPredictor.sv
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@ -33,11 +33,11 @@ module RASPredictor #(parameter int StackSize = 16 )(
input logic clk,
input logic reset,
input logic StallF, StallD, StallE, StallM, FlushD, FlushE, FlushM,
input logic WrongBPRetD, // Prediction class is wrong
input logic RetD,
input logic RetE, JalE, // Instr class
input logic BPRetF,
input logic [`XLEN-1:0] PCLinkE, // PC of instruction after a jal
input logic WrongBPReturnD, // Prediction class is wrong
input logic ReturnD,
input logic ReturnE, CallE, // Instr class
input logic BPReturnF,
input logic [`XLEN-1:0] PCLinkE, // PC of instruction after a call
output logic [`XLEN-1:0] RASPCF // Top of the stack
);
@ -54,21 +54,21 @@ module RASPredictor #(parameter int StackSize = 16 )(
logic IncrRepairD, DecRepairD;
logic DecrementPtr;
logic FlushedRetDE;
logic WrongPredRetD;
logic FlushedReturnDE;
logic WrongPredReturnD;
assign PopF = BPRetF & ~StallD & ~FlushD;
assign PushE = JalE & ~StallM & ~FlushM;
assign PopF = BPReturnF & ~StallD & ~FlushD;
assign PushE = CallE & ~StallM & ~FlushM;
assign WrongPredRetD = (WrongBPRetD) & ~StallE & ~FlushE;
assign FlushedRetDE = (~StallE & FlushE & RetD) | (~StallM & FlushM & RetE); // flushed ret
assign WrongPredReturnD = (WrongBPReturnD) & ~StallE & ~FlushE;
assign FlushedReturnDE = (~StallE & FlushE & ReturnD) | (~StallM & FlushM & ReturnE); // flushed return
assign RepairD = WrongPredRetD | FlushedRetDE ;
assign RepairD = WrongPredReturnD | FlushedReturnDE ;
assign IncrRepairD = FlushedRetDE | (WrongPredRetD & ~RetD); // Guessed it was a ret, but its not
assign IncrRepairD = FlushedReturnDE | (WrongPredReturnD & ~ReturnD); // Guessed it was a return, but its not
assign DecRepairD = WrongPredRetD & RetD; // Guessed non ret but is a ret.
assign DecRepairD = WrongPredReturnD & ReturnD; // Guessed non return but is a return.
assign CounterEn = PopF | PushE | RepairD;

105
src/ifu/bpred/bpred.sv
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@ -58,8 +58,8 @@ module bpred (
input logic [`XLEN-1:0] IEUAdrE, // The branch/jump target address
input logic [`XLEN-1:0] IEUAdrM, // The branch/jump target address
input logic [`XLEN-1:0] PCLinkE, // The address following the branch instruction. (AKA Fall through address)
output logic [3:0] InstrClassM, // The valid instruction class. 1-hot encoded as jalr, ret, jr (not ret), j, br
output logic JumpOrTakenBranchM, // The valid instruction class. 1-hot encoded as jalr, ret, jr (not ret), j, br
output logic [3:0] InstrClassM, // The valid instruction class. 1-hot encoded as call, return, jr (not return), j, br
output logic JumpOrTakenBranchM, // The valid instruction class. 1-hot encoded as call, return, jr (not return), j, br
// Report branch prediction status
output logic BPPredWrongE, // Prediction is wrong
@ -88,14 +88,14 @@ module bpred (
logic [`XLEN-1:0] BTAD;
logic BTBJalF, BTBRetF, BTBJumpF, BTBBranchF;
logic BPBranchF, BPJumpF, BPRetF, BPJalF;
logic BPBranchD, BPJumpD, BPRetD, BPJalD;
logic RetD, JalD;
logic RetE, JalE;
logic BranchM, JumpM, RetM, JalM;
logic BranchW, JumpW, RetW, JalW;
logic WrongBPRetD;
logic BTBCallF, BTBReturnF, BTBJumpF, BTBBranchF;
logic BPBranchF, BPJumpF, BPReturnF, BPCallF;
logic BPBranchD, BPJumpD, BPReturnD, BPCallD;
logic ReturnD, CallD;
logic ReturnE, CallE;
logic BranchM, JumpM, ReturnM, CallM;
logic BranchW, JumpW, ReturnW, CallW;
logic WrongBPReturnD;
logic [`XLEN-1:0] PCW, IEUAdrW;
// Part 1 branch direction prediction
@ -150,72 +150,28 @@ module bpred (
TargetPredictor(.clk, .reset, .StallF, .StallD, .StallE, .StallM, .StallW, .FlushD, .FlushE, .FlushM, .FlushW,
.PCNextF, .PCF, .PCD, .PCE, .PCM, .PCW,
.BTAF, .BTAD,
.BTBIClassF({BTBJalF, BTBRetF, BTBJumpF, BTBBranchF}),
.BTBIClassF({BTBCallF, BTBReturnF, BTBJumpF, BTBBranchF}),
.PredictionInstrClassWrongM,
.IEUAdrE, .IEUAdrM, .IEUAdrW,
.InstrClassD({JalD, RetD, JumpD, BranchD}), .InstrClassE({JalE, RetE, JumpE, BranchE}), .InstrClassM({JalM, RetM, JumpM, BranchM}),
.InstrClassW({JalW, RetW, JumpW, BranchW}));
.InstrClassD({CallD, ReturnD, JumpD, BranchD}), .InstrClassE({CallE, ReturnE, JumpE, BranchE}), .InstrClassM({CallM, ReturnM, JumpM, BranchM}),
.InstrClassW({CallW, ReturnW, JumpW, BranchW}));
if (!`INSTR_CLASS_PRED) begin : DirectClassDecode
// This section is mainly for testing, verification, and PPA comparison.
// An alternative to using the BTB to store the instruction class is to partially decode
// the instructions in the Fetch stage into, Jal, Ret, Jump, and Branch instructions.
// This logic is not described in the text book as of 23 February 2023.
logic cjal, cj, cjr, cjalr, CJumpF, CBranchF;
logic NCJumpF, NCBranchF;
if(`C_SUPPORTED) begin
logic [4:0] CompressedOpcF;
assign CompressedOpcF = {PostSpillInstrRawF[1:0], PostSpillInstrRawF[15:13]};
assign cjal = CompressedOpcF == 5'h09 & `XLEN == 32;
assign cj = CompressedOpcF == 5'h0d;
assign cjr = CompressedOpcF == 5'h14 & ~PostSpillInstrRawF[12] & PostSpillInstrRawF[6:2] == 5'b0 & PostSpillInstrRawF[11:7] != 5'b0;
assign cjalr = CompressedOpcF == 5'h14 & PostSpillInstrRawF[12] & PostSpillInstrRawF[6:2] == 5'b0 & PostSpillInstrRawF[11:7] != 5'b0;
assign CJumpF = cjal | cj | cjr | cjalr;
assign CBranchF = CompressedOpcF[4:1] == 4'h7;
end else begin
assign {cjal, cj, cjr, cjalr, CJumpF, CBranchF} = '0;
end
icpred icpred(.clk, .reset, .StallF, .StallD, .StallE, .StallM, .StallW, .FlushD, .FlushE, .FlushM, .FlushW,
.PostSpillInstrRawF, .InstrD, .BranchD, .BranchE, .JumpD, .JumpE, .BranchM, .BranchW, .JumpM, .JumpW,
.CallD, .CallE, .CallM, .CallW, .ReturnD, .ReturnE, .ReturnM, .ReturnW, .BTBCallF, .BTBReturnF, .BTBJumpF, .BTBBranchF,
.BPCallF, .BPReturnF, .BPJumpF, .BPBranchF, .PredictionInstrClassWrongM, .WrongBPReturnD);
assign NCJumpF = PostSpillInstrRawF[6:0] == 7'h67 | PostSpillInstrRawF[6:0] == 7'h6F;
assign NCBranchF = PostSpillInstrRawF[6:0] == 7'h63;
assign BPBranchF = NCBranchF | (`C_SUPPORTED & CBranchF);
assign BPJumpF = NCJumpF | (`C_SUPPORTED & (CJumpF));
assign BPRetF = (NCJumpF & (PostSpillInstrRawF[19:15] & 5'h1B) == 5'h01) | // return must return to ra or r5
(`C_SUPPORTED & (cjalr | cjr) & ((PostSpillInstrRawF[11:7] & 5'h1B) == 5'h01));
assign BPJalF = (NCJumpF & (PostSpillInstrRawF[11:07] & 5'h1B) == 5'h01) | // jal(r) must link to ra or x5
(`C_SUPPORTED & (cjal | (cjalr & (PostSpillInstrRawF[11:7] & 5'h1b) == 5'h01)));
end else begin
// This section connects the BTB's instruction class prediction.
assign {BPJalF, BPRetF, BPJumpF, BPBranchF} = {BTBJalF, BTBRetF, BTBJumpF, BTBBranchF};
end
assign BPPCSrcF = (BPBranchF & BPDirPredF[1]) | BPJumpF;
// Part 3 RAS
RASPredictor RASPredictor(.clk, .reset, .StallF, .StallD, .StallE, .StallM, .FlushD, .FlushE, .FlushM,
.BPRetF, .RetD, .RetE, .JalE,
.WrongBPRetD, .RASPCF, .PCLinkE);
assign BPPredPCF = BPRetF ? RASPCF : BTAF;
assign RetD = JumpD & (InstrD[19:15] & 5'h1B) == 5'h01; // return must return to ra or x5
assign JalD = JumpD & (InstrD[11:7] & 5'h1B) == 5'h01; // jal(r) must link to ra or x5
flopenrc #(2) InstrClassRegE(clk, reset, FlushE, ~StallE, {JalD, RetD}, {JalE, RetE});
flopenrc #(4) InstrClassRegM(clk, reset, FlushM, ~StallM, {JalE, RetE, JumpE, BranchE}, {JalM, RetM, JumpM, BranchM});
flopenrc #(4) InstrClassRegW(clk, reset, FlushM, ~StallW, {JalM, RetM, JumpM, BranchM}, {JalW, RetW, JumpW, BranchW});
assign BPPCSrcF = (BPBranchF & BPDirPredF[1]) | BPJumpF;
flopenrc #(1) BPPredWrongMReg(clk, reset, FlushM, ~StallM, BPPredWrongE, BPPredWrongM);
// branch predictor
flopenrc #(1) BPClassWrongRegM(clk, reset, FlushM, ~StallM, AnyWrongPredInstrClassE, PredictionInstrClassWrongM);
flopenrc #(1) WrongInstrClassRegE(clk, reset, FlushE, ~StallE, AnyWrongPredInstrClassD, AnyWrongPredInstrClassE);
// Part 3 RAS
RASPredictor RASPredictor(.clk, .reset, .StallF, .StallD, .StallE, .StallM, .FlushD, .FlushE, .FlushM,
.BPReturnF, .ReturnD, .ReturnE, .CallE,
.WrongBPReturnD, .RASPCF, .PCLinkE);
assign BPPredPCF = BPReturnF ? RASPCF : BTAF;
// pipeline the predicted class
flopenrc #(4) PredInstrClassRegD(clk, reset, FlushD, ~StallD, {BPJalF, BPRetF, BPJumpF, BPBranchF}, {BPJalD, BPRetD, BPJumpD, BPBranchD});
// Check the prediction
// if it is a CFI then check if the next instruction address (PCD) matches the branch's target or fallthrough address.
// if the class prediction is wrong a regular instruction may have been predicted as a taken branch
@ -223,17 +179,14 @@ module bpred (
// The next instruction is always valid as no other flush would occur at the same time as the branch and not
// also flush the branch. This will change in a superscaler cpu.
assign PredictionPCWrongE = PCCorrectE != PCD;
// branch class prediction wrong.
assign AnyWrongPredInstrClassD = |({BPJalD, BPRetD, BPJumpD, BPBranchD} ^ {JalD, RetD, JumpD, BranchD});
assign WrongBPRetD = BPRetD ^ RetD;
// branch is wrong only if the PC does not match and both the Decode and Fetch stages have valid instructions.
assign BPPredWrongE = PredictionPCWrongE & InstrValidE & InstrValidD;
// *** clean up old signal names for testing.
logic BPPredWrongEAlt;
logic NotMatch;
assign BPPredWrongEAlt = PredictionPCWrongE & InstrValidE & InstrValidD; // this does not work for cubic benchmark
assign BPPredWrongEAlt = PredictionPCWrongE & InstrValidE & InstrValidD;
assign NotMatch = BPPredWrongE != BPPredWrongEAlt;
// Output the predicted PC or corrected PC on miss-predict.
@ -263,8 +216,8 @@ module bpred (
// could be wrong or the fall through address selected for branch predict not taken.
// By pipeline the BTB's PC and RAS address through the pipeline we can measure the accuracy of
// both without the above inaccuracies.
assign BTBPredPCWrongE = (BTAE != IEUAdrE) & (BranchE | JumpE & ~RetE) & PCSrcE;
assign RASPredPCWrongE = (RASPCE != IEUAdrE) & RetE & PCSrcE;
assign BTBPredPCWrongE = (BTAE != IEUAdrE) & (BranchE | JumpE & ~ReturnE) & PCSrcE;
assign RASPredPCWrongE = (RASPCE != IEUAdrE) & ReturnE & PCSrcE;
assign JumpOrTakenBranchE = (BranchE & PCSrcE) | JumpE;
@ -283,7 +236,7 @@ module bpred (
end
// **** Fix me
assign InstrClassM = {JalM, RetM, JumpM, BranchM};
assign InstrClassM = {CallM, ReturnM, JumpM, BranchM};
flopenr #(`XLEN) PCWReg(clk, reset, ~StallW, PCM, PCW);
flopenr #(`XLEN) IEUAdrWReg(clk, reset, ~StallW, IEUAdrM, IEUAdrW);

107
src/ifu/bpred/icpred.sv Normal file
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@ -0,0 +1,107 @@
///////////////////////////////////////////
// icpred.sv
//
// Written: Ross Thomposn ross1728@gmail.com
// Created: February 26, 2023
// Modified: February 26, 2023
//
// Purpose: Partial decode of instructions into control flow instructions (cfi)P
// Call, Return, Jump, and Branch
//
// A component of the CORE-V-WALLY configurable RISC-V project.
//
// Copyright (C) 2021-23 Harvey Mudd College & Oklahoma State University
//
// SPDX-License-Identifier: Apache-2.0 WITH SHL-2.1
//
// Licensed under the Solderpad Hardware License v 2.1 (the “License”); you may not use this file
// except in compliance with the License, or, at your option, the Apache License version 2.0. You
// may obtain a copy of the License at
//
// https://solderpad.org/licenses/SHL-2.1/
//
// Unless required by applicable law or agreed to in writing, any work distributed under the
// License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
// either express or implied. See the License for the specific language governing permissions
// and limitations under the License.
////////////////////////////////////////////////////////////////////////////////////////////////
`include "wally-config.vh"
`define INSTR_CLASS_PRED 1
module icpred (
input logic clk, reset,
input logic StallF, StallD, StallE, StallM, StallW,
input logic FlushD, FlushE, FlushM, FlushW,
input logic [31:0] PostSpillInstrRawF, InstrD, // Instruction
input logic BranchD, BranchE,
input logic JumpD, JumpE,
output logic BranchM, BranchW,
output logic JumpM, JumpW,
output logic CallD, CallE, CallM, CallW,
output logic ReturnD, ReturnE, ReturnM, ReturnW,
input logic BTBCallF, BTBReturnF, BTBJumpF, BTBBranchF,
output logic BPCallF, BPReturnF, BPJumpF, BPBranchF,
output logic PredictionInstrClassWrongM, WrongBPReturnD
);
logic AnyWrongPredInstrClassD, AnyWrongPredInstrClassE;
logic BPBranchD, BPJumpD, BPReturnD, BPCallD;
if (!`INSTR_CLASS_PRED) begin : DirectClassDecode
// This section is mainly for testing, verification, and PPA comparison.
// An alternative to using the BTB to store the instruction class is to partially decode
// the instructions in the Fetch stage into, Call, Return, Jump, and Branch instructions.
// This logic is not described in the text book as of 23 February 2023.
logic ccall, cj, cjr, ccallr, CJumpF, CBranchF;
logic NCJumpF, NCBranchF;
if(`C_SUPPORTED) begin
logic [4:0] CompressedOpcF;
assign CompressedOpcF = {PostSpillInstrRawF[1:0], PostSpillInstrRawF[15:13]};
assign ccall = CompressedOpcF == 5'h09 & `XLEN == 32;
assign cj = CompressedOpcF == 5'h0d;
assign cjr = CompressedOpcF == 5'h14 & ~PostSpillInstrRawF[12] & PostSpillInstrRawF[6:2] == 5'b0 & PostSpillInstrRawF[11:7] != 5'b0;
assign ccallr = CompressedOpcF == 5'h14 & PostSpillInstrRawF[12] & PostSpillInstrRawF[6:2] == 5'b0 & PostSpillInstrRawF[11:7] != 5'b0;
assign CJumpF = ccall | cj | cjr | ccallr;
assign CBranchF = CompressedOpcF[4:1] == 4'h7;
end else begin
assign {ccall, cj, cjr, ccallr, CJumpF, CBranchF} = '0;
end
assign NCJumpF = PostSpillInstrRawF[6:0] == 7'h67 | PostSpillInstrRawF[6:0] == 7'h6F;
assign NCBranchF = PostSpillInstrRawF[6:0] == 7'h63;
assign BPBranchF = NCBranchF | (`C_SUPPORTED & CBranchF);
assign BPJumpF = NCJumpF | (`C_SUPPORTED & (CJumpF));
assign BPReturnF = (NCJumpF & (PostSpillInstrRawF[19:15] & 5'h1B) == 5'h01) | // returnurn must returnurn to ra or r5
(`C_SUPPORTED & (ccallr | cjr) & ((PostSpillInstrRawF[11:7] & 5'h1B) == 5'h01));
assign BPCallF = (NCJumpF & (PostSpillInstrRawF[11:07] & 5'h1B) == 5'h01) | // call(r) must link to ra or x5
(`C_SUPPORTED & (ccall | (ccallr & (PostSpillInstrRawF[11:7] & 5'h1b) == 5'h01)));
end else begin
// This section connects the BTB's instruction class prediction.
assign {BPCallF, BPReturnF, BPJumpF, BPBranchF} = {BTBCallF, BTBReturnF, BTBJumpF, BTBBranchF};
end
assign ReturnD = JumpD & (InstrD[19:15] & 5'h1B) == 5'h01; // returnurn must returnurn to ra or x5
assign CallD = JumpD & (InstrD[11:7] & 5'h1B) == 5'h01; // call(r) must link to ra or x5
flopenrc #(2) InstrClassRegE(clk, reset, FlushE, ~StallE, {CallD, ReturnD}, {CallE, ReturnE});
flopenrc #(4) InstrClassRegM(clk, reset, FlushM, ~StallM, {CallE, ReturnE, JumpE, BranchE}, {CallM, ReturnM, JumpM, BranchM});
flopenrc #(4) InstrClassRegW(clk, reset, FlushM, ~StallW, {CallM, ReturnM, JumpM, BranchM}, {CallW, ReturnW, JumpW, BranchW});
// branch predictor
flopenrc #(1) BPClassWrongRegM(clk, reset, FlushM, ~StallM, AnyWrongPredInstrClassE, PredictionInstrClassWrongM);
flopenrc #(1) WrongInstrClassRegE(clk, reset, FlushE, ~StallE, AnyWrongPredInstrClassD, AnyWrongPredInstrClassE);
// pipeline the predicted class
flopenrc #(4) PredInstrClassRegD(clk, reset, FlushD, ~StallD, {BPCallF, BPReturnF, BPJumpF, BPBranchF}, {BPCallD, BPReturnD, BPJumpD, BPBranchD});
// branch class prediction wrong.
assign AnyWrongPredInstrClassD = |({BPCallD, BPReturnD, BPJumpD, BPBranchD} ^ {CallD, ReturnD, JumpD, BranchD});
assign WrongBPReturnD = BPReturnD ^ ReturnD;
endmodule