riscv/rocket-chip
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Improve ALU QoR

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Rejigger muxes; share XOR gates between ADD/SUB, XOR, and BEQ.
This commit is contained in:
Andrew Waterman 2016-01-20 17:42:31 -08:00
parent 77e068c153
commit 52d6b0b1a5
1 changed files with 25 additions and 25 deletions
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50
rocket/src/main/scala/dpath_alu.scala
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@ -12,12 +12,12 @@ object ALU
val FN_X = BitPat("b????") val FN_X = BitPat("b????")
val FN_ADD = UInt(0) val FN_ADD = UInt(0)
val FN_SL = UInt(1) val FN_SL = UInt(1)
val FN_SEQ = UInt(2)
val FN_SNE = UInt(3)
val FN_XOR = UInt(4) val FN_XOR = UInt(4)
val FN_SR = UInt(5)
val FN_OR = UInt(6) val FN_OR = UInt(6)
val FN_AND = UInt(7) val FN_AND = UInt(7)
val FN_SR = UInt(5)
val FN_SEQ = UInt(8)
val FN_SNE = UInt(9)
val FN_SUB = UInt(10) val FN_SUB = UInt(10)
val FN_SRA = UInt(11) val FN_SRA = UInt(11)
val FN_SLT = UInt(12) val FN_SLT = UInt(12)
@ -35,11 +35,12 @@ object ALU
val FN_MULHSU = FN_SLT val FN_MULHSU = FN_SLT
val FN_MULHU = FN_SLTU val FN_MULHU = FN_SLTU
def isMulFN(fn: Bits, cmp: Bits) = fn(1,0) === cmp(1,0) def isMulFN(fn: UInt, cmp: UInt) = fn(1,0) === cmp(1,0)
def isSub(cmd: Bits) = cmd(3) def isSub(cmd: UInt) = cmd(3)
def cmpUnsigned(cmd: Bits) = cmd(1) def isCmp(cmd: UInt) = cmd === FN_SEQ || cmd === FN_SNE || cmd >= FN_SLT
def cmpInverted(cmd: Bits) = cmd(0) def cmpUnsigned(cmd: UInt) = cmd(1)
def cmpEq(cmd: Bits) = !cmd(2) def cmpInverted(cmd: UInt) = cmd(0)
def cmpEq(cmd: UInt) = !cmd(3)
} }
import ALU._ import ALU._
@ -51,43 +52,42 @@ class ALU(implicit p: Parameters) extends CoreModule()(p) {
val in1 = UInt(INPUT, xLen) val in1 = UInt(INPUT, xLen)
val out = UInt(OUTPUT, xLen) val out = UInt(OUTPUT, xLen)
val adder_out = UInt(OUTPUT, xLen) val adder_out = UInt(OUTPUT, xLen)
val cmp_out = Bool(OUTPUT)
} }
// ADD, SUB // ADD, SUB
val sum = io.in1 + Mux(isSub(io.fn), -io.in2, io.in2) val in2_inv = Mux(isSub(io.fn), ~io.in2, io.in2)
val in1_xor_in2 = io.in1 ^ in2_inv
io.adder_out := io.in1 + in2_inv + isSub(io.fn)
// SLT, SLTU // SLT, SLTU
val cmp = cmpInverted(io.fn) ^ io.cmp_out := cmpInverted(io.fn) ^
Mux(cmpEq(io.fn), sum === UInt(0), Mux(cmpEq(io.fn), in1_xor_in2 === UInt(0),
Mux(io.in1(xLen-1) === io.in2(xLen-1), sum(xLen-1), Mux(io.in1(xLen-1) === io.in2(xLen-1), io.adder_out(xLen-1),
Mux(cmpUnsigned(io.fn), io.in2(xLen-1), io.in1(xLen-1)))) Mux(cmpUnsigned(io.fn), io.in2(xLen-1), io.in1(xLen-1))))
// SLL, SRL, SRA // SLL, SRL, SRA
val full_shamt = io.in2(log2Up(xLen)-1,0)
val (shamt, shin_r) = val (shamt, shin_r) =
if (xLen == 32) (full_shamt, io.in1) if (xLen == 32) (io.in2(4,0), io.in1)
else { else {
require(xLen == 64) require(xLen == 64)
val shin_hi_32 = Fill(32, isSub(io.fn) && io.in1(31)) val shin_hi_32 = Fill(32, isSub(io.fn) && io.in1(31))
val shin_hi = Mux(io.dw === DW_64, io.in1(63,32), shin_hi_32) val shin_hi = Mux(io.dw === DW_64, io.in1(63,32), shin_hi_32)
val shamt = Cat(full_shamt(5) & (io.dw === DW_64), full_shamt(4,0)) val shamt = Cat(io.in2(5) & (io.dw === DW_64), io.in2(4,0))
(shamt, Cat(shin_hi, io.in1(31,0))) (shamt, Cat(shin_hi, io.in1(31,0)))
} }
val shin = Mux(io.fn === FN_SR || io.fn === FN_SRA, shin_r, Reverse(shin_r)) val shin = Mux(io.fn === FN_SR || io.fn === FN_SRA, shin_r, Reverse(shin_r))
val shout_r = (Cat(isSub(io.fn) & shin(xLen-1), shin).toSInt >> shamt)(xLen-1,0) val shout_r = (Cat(isSub(io.fn) & shin(xLen-1), shin).toSInt >> shamt)(xLen-1,0)
val shout_l = Reverse(shout_r) val shout_l = Reverse(shout_r)
val shout = Mux(io.fn === FN_SR || io.fn === FN_SRA, shout_r, UInt(0)) |
Mux(io.fn === FN_SL, shout_l, UInt(0))
val out = // AND, OR, XOR
Mux(io.fn === FN_ADD || io.fn === FN_SUB, sum, val logic = Mux(io.fn === FN_XOR || io.fn === FN_OR, in1_xor_in2, UInt(0)) |
Mux(io.fn === FN_SR || io.fn === FN_SRA, shout_r, Mux(io.fn === FN_OR || io.fn === FN_AND, io.in1 & io.in2, UInt(0))
Mux(io.fn === FN_SL, shout_l, val shift_logic = (isCmp(io.fn) && io.cmp_out) | logic | shout
Mux(io.fn === FN_AND, io.in1 & io.in2, val out = Mux(io.fn === FN_ADD || io.fn === FN_SUB, io.adder_out, shift_logic)
Mux(io.fn === FN_OR, io.in1 | io.in2,
Mux(io.fn === FN_XOR, io.in1 ^ io.in2,
/* all comparisons */ cmp))))))
io.adder_out := sum
io.out := out io.out := out
if (xLen > 32) { if (xLen > 32) {
require(xLen == 64) require(xLen == 64)