riscv/rocket-chip
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Don't merge stores that manifest WAW hazards

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The following sequence would drop the first store when eccBytes=4:

    sb x0, 0(t0)
    nop
    sb x0, 4(t0)
    nop
    sb x0, 1(t0)

Because the first and second store are to different ECC granules, the
hazard check correctly allowed the second one to proceed, but the third
was merged with the second, even though it conflicted with the first.
So, don't allow the third to be merged with the second, since the second
stored to a different ECC granule.
This commit is contained in:
Andrew Waterman 2017-08-08 15:12:40 -07:00
parent 3ef6e4c9f2
commit 809c7e8551
1 changed files with 8 additions and 5 deletions
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13
src/main/scala/rocket/DCache.scala
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@ -312,11 +312,6 @@ class DCacheModule(outer: DCache) extends HellaCacheModule(outer) {
pstore2_valid := pstore2_valid && !pstore_drain || advance_pstore1
val pstore2_addr = RegEnable(Mux(s2_correct, s2_req.addr, pstore1_addr), advance_pstore1)
val pstore2_way = RegEnable(Mux(s2_correct, s2_hit_way, pstore1_way), advance_pstore1)
s2_store_merge := {
val idxMatch = s2_req.addr(untagBits-1, log2Ceil(wordBytes)) === pstore2_addr(untagBits-1, log2Ceil(wordBytes))
val tagMatch = (s2_hit_way & pstore2_way).orR
Bool(eccBytes > 1) && pstore2_valid && idxMatch && tagMatch
}
val pstore2_storegen_data = {
for (i <- 0 until wordBytes)
yield RegEnable(pstore1_storegen_data(8*(i+1)-1, 8*i), advance_pstore1 || pstore1_merge && pstore1_mask(i))
@ -329,6 +324,14 @@ class DCacheModule(outer: DCache) extends HellaCacheModule(outer) {
}
mask
}
s2_store_merge := {
// only merge stores to ECC granules that are already stored-to, to avoid
// WAW hazards
val wordMatch = (eccMask(pstore2_storegen_mask) | ~eccMask(pstore1_mask)).andR
val idxMatch = s2_req.addr(untagBits-1, log2Ceil(wordBytes)) === pstore2_addr(untagBits-1, log2Ceil(wordBytes))
val tagMatch = (s2_hit_way & pstore2_way).orR
Bool(eccBytes > 1) && pstore2_valid && wordMatch && idxMatch && tagMatch
}
dataArb.io.in(0).valid := pstore_drain
dataArb.io.in(0).bits.write := true
dataArb.io.in(0).bits.addr := Mux(pstore2_valid, pstore2_addr, pstore1_addr)