riscv/rocket-chip
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Mitigate some I$ response valid critical paths

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This commit is contained in:
Andrew Waterman 2017-08-01 15:24:58 -07:00
parent 2ecea2ef60
commit 735701382f
1 changed files with 14 additions and 11 deletions
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17
src/main/scala/rocket/Frontend.scala
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@ -180,7 +180,7 @@ class FrontendModule(outer: Frontend) extends LazyModuleImp(outer)
Mux(returnAddrLSBs(log2Ceil(fetchWidth)), ntpc, s1_base_pc | ((returnAddrLSBs << log2Ceil(coreInstBytes)) & (fetchBytes - 1))) Mux(returnAddrLSBs(log2Ceil(fetchWidth)), ntpc, s1_base_pc | ((returnAddrLSBs << log2Ceil(coreInstBytes)) & (fetchBytes - 1)))
btb.io.ras_update.bits.cfiType := btb.io.resp.bits.cfiType btb.io.ras_update.bits.cfiType := btb.io.resp.bits.cfiType
btb.io.ras_update.bits.prediction.valid := true btb.io.ras_update.bits.prediction.valid := true
} else when (fq.io.enq.fire()) { } else {
val s2_btb_hit = s2_btb_resp_valid && s2_btb_resp_bits.taken val s2_btb_hit = s2_btb_resp_valid && s2_btb_resp_bits.taken
val s2_base_pc = ~(~s2_pc | (fetchBytes-1)) val s2_base_pc = ~(~s2_pc | (fetchBytes-1))
val taken_idx = Wire(UInt()) val taken_idx = Wire(UInt())
@ -213,7 +213,7 @@ class FrontendModule(outer: Frontend) extends LazyModuleImp(outer)
when (!prevTaken) { when (!prevTaken) {
taken_idx := idx taken_idx := idx
after_idx := idx + 1 after_idx := idx + 1
btb.io.ras_update.valid := !s2_wrong_path && (prevRVI && (rviCall || rviReturn) || valid && (rvcCall || rvcReturn)) btb.io.ras_update.valid := fq.io.enq.fire() && !s2_wrong_path && (prevRVI && (rviCall || rviReturn) || valid && (rvcCall || rvcReturn))
btb.io.ras_update.bits.prediction.valid := true btb.io.ras_update.bits.prediction.valid := true
btb.io.ras_update.bits.cfiType := Mux(Mux(prevRVI, rviReturn, rvcReturn), CFIType.ret, CFIType.call) btb.io.ras_update.bits.cfiType := Mux(Mux(prevRVI, rviReturn, rvcReturn), CFIType.ret, CFIType.call)
@ -222,7 +222,7 @@ class FrontendModule(outer: Frontend) extends LazyModuleImp(outer)
valid && (rvcJALR || (rvcJR && !btb.io.ras_head.valid))) { valid && (rvcJALR || (rvcJR && !btb.io.ras_head.valid))) {
s2_wrong_path := true s2_wrong_path := true
} }
when (taken) { when (s2_valid && taken) {
val pc = s2_base_pc | (idx*coreInstBytes) val pc = s2_base_pc | (idx*coreInstBytes)
val npc = val npc =
if (idx == 0) pc.asSInt + Mux(prevRVI, rviImm -& 2.S, rvcImm) if (idx == 0) pc.asSInt + Mux(prevRVI, rviImm -& 2.S, rvcImm)
@ -231,18 +231,20 @@ class FrontendModule(outer: Frontend) extends LazyModuleImp(outer)
} }
when (prevRVI && rviBranch || valid && rvcBranch) { when (prevRVI && rviBranch || valid && rvcBranch) {
btb.io.bht_advance.valid := !s2_wrong_path && !s2_btb_resp_valid btb.io.bht_advance.valid := fq.io.enq.fire() && !s2_wrong_path && !s2_btb_resp_valid
btb.io.bht_advance.bits := s2_btb_resp_bits btb.io.bht_advance.bits := s2_btb_resp_bits
} }
} }
} }
if (idx == fetchWidth-1) { if (idx == fetchWidth-1) {
when (fq.io.enq.fire()) {
s2_partial_insn_valid := false s2_partial_insn_valid := false
when (valid && !prevTaken && !rvc) { when (valid && !prevTaken && !rvc) {
s2_partial_insn_valid := true s2_partial_insn_valid := true
s2_partial_insn := bits | 0x3 s2_partial_insn := bits | 0x3
} }
}
prevTaken || taken prevTaken || taken
} else { } else {
scanInsns(idx + 1, valid, bits, prevTaken || taken) scanInsns(idx + 1, valid, bits, prevTaken || taken)
@ -252,15 +254,16 @@ class FrontendModule(outer: Frontend) extends LazyModuleImp(outer)
btb.io.ras_update.bits.returnAddr := s2_base_pc + (after_idx << log2Ceil(coreInstBytes)) btb.io.ras_update.bits.returnAddr := s2_base_pc + (after_idx << log2Ceil(coreInstBytes))
val taken = scanInsns(0, s2_partial_insn_valid, s2_partial_insn, false.B) val taken = scanInsns(0, s2_partial_insn_valid, s2_partial_insn, false.B)
when (s2_btb_hit) { when (fq.io.enq.fire() && s2_btb_hit) {
s2_partial_insn_valid := false s2_partial_insn_valid := false
}.otherwise { }
when (!s2_btb_hit) {
fq.io.enq.bits.btb.bits.bridx := taken_idx fq.io.enq.bits.btb.bits.bridx := taken_idx
when (taken) { when (taken) {
fq.io.enq.bits.btb.valid := true fq.io.enq.bits.btb.valid := true
fq.io.enq.bits.btb.bits.taken := true fq.io.enq.bits.btb.bits.taken := true
fq.io.enq.bits.btb.bits.entry := UInt(tileParams.btb.get.nEntries) fq.io.enq.bits.btb.bits.entry := UInt(tileParams.btb.get.nEntries)
s2_redirect := true when (fq.io.enq.fire()) { s2_redirect := true }
} }
} }
} }