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Split last read and first write analysis (#17137)

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* Split last read and first write analysis

This improves performance by 10% for some
cases.

* Remove outdated comments
This commit is contained in:
Clyybber 2021-02-21 16:20:05 +01:00 • committed by GitHub
commit 6b7a6f8c54
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GPG key ID: 4AEE18F83AFDEB23
1 changed files with 42 additions and 20 deletions
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62
compiler/injectdestructors.nim
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@ -82,7 +82,7 @@ proc aliasesCached(cache: var AliasCache, obj, field: PNode): AliasKind =
cache[key] = aliases(obj, field)
cache[key]
proc collectLastReads(cfg: ControlFlowGraph; cache: var AliasCache, alreadySeen: var HashSet[PNode], lastReads, potLastReads: var IntSet; pc: var int, until: int) =
proc collectLastReads(cfg: ControlFlowGraph; cache: var AliasCache, lastReads, potLastReads: var IntSet; pc: var int, until: int) =
template aliasesCached(obj, field: PNode): untyped =
aliasesCached(cache, obj, field)
while pc < until:
@ -100,15 +100,6 @@ proc collectLastReads(cfg: ControlFlowGraph; cache: var AliasCache, alreadySeen:
cfg[r].n.comment = '\n' & $pc
potLastReads.excl r
var alreadySeenThisNode = false
for s in alreadySeen:
if cfg[pc].n.aliases(s) != no or s.aliases(cfg[pc].n) != no:
alreadySeenThisNode = true; break
if alreadySeenThisNode: cfg[pc].n.flags.excl nfFirstWrite
else: cfg[pc].n.flags.incl nfFirstWrite
alreadySeen.incl cfg[pc].n
inc pc
of use:
let potLastReadsCopy = potLastReads
@ -119,25 +110,19 @@ proc collectLastReads(cfg: ControlFlowGraph; cache: var AliasCache, alreadySeen:
potLastReads.incl pc
alreadySeen.incl cfg[pc].n
inc pc
of goto:
pc += cfg[pc].dest
of fork:
# every branch must lead to the last read of the location:
var variantA = pc + 1
var variantB = pc + cfg[pc].dest
var potLastReadsA, potLastReadsB = potLastReads
var lastReadsA, lastReadsB: IntSet
var alreadySeenA, alreadySeenB = alreadySeen
while variantA != variantB and max(variantA, variantB) < cfg.len and min(variantA, variantB) < until:
if variantA < variantB:
collectLastReads(cfg, cache, alreadySeenA, lastReadsA, potLastReadsA, variantA, min(variantB, until))
collectLastReads(cfg, cache, lastReadsA, potLastReadsA, variantA, min(variantB, until))
else:
collectLastReads(cfg, cache, alreadySeenB, lastReadsB, potLastReadsB, variantB, min(variantA, until))
alreadySeen.incl alreadySeenA + alreadySeenB
collectLastReads(cfg, cache, lastReadsB, potLastReadsB, variantB, min(variantA, until))
# Add those last reads that were turned into last reads on both branches
lastReads.incl lastReadsA * lastReadsB
@ -157,6 +142,40 @@ proc collectLastReads(cfg: ControlFlowGraph; cache: var AliasCache, alreadySeen:
pc = min(variantA, variantB)
proc collectFirstWrites(cfg: ControlFlowGraph; alreadySeen: var HashSet[PNode]; pc: var int, until: int) =
while pc < until:
case cfg[pc].kind
of def:
var alreadySeenThisNode = false
for s in alreadySeen:
if cfg[pc].n.aliases(s) != no or s.aliases(cfg[pc].n) != no:
alreadySeenThisNode = true; break
if alreadySeenThisNode: cfg[pc].n.flags.excl nfFirstWrite
else: cfg[pc].n.flags.incl nfFirstWrite
alreadySeen.incl cfg[pc].n
inc pc
of use:
alreadySeen.incl cfg[pc].n
inc pc
of goto:
pc += cfg[pc].dest
of fork:
var variantA = pc + 1
var variantB = pc + cfg[pc].dest
var alreadySeenA, alreadySeenB = alreadySeen
while variantA != variantB and max(variantA, variantB) < cfg.len and min(variantA, variantB) < until:
if variantA < variantB:
collectFirstWrites(cfg, alreadySeenA, variantA, min(variantB, until))
else:
collectFirstWrites(cfg, alreadySeenB, variantB, min(variantA, until))
alreadySeen.incl alreadySeenA + alreadySeenB
pc = min(variantA, variantB)
proc isLastRead(n: PNode; c: var Con): bool =
let m = dfa.skipConvDfa(n)
(m.kind == nkSym and sfSingleUsedTemp in m.sym.flags) or nfLastRead in m.flags
@ -1086,10 +1105,9 @@ proc injectDestructorCalls*(g: ModuleGraph; idgen: IdGenerator; owner: PSym; n:
block:
var cache = initTable[(PNode, PNode), AliasKind]()
var alreadySeen: HashSet[PNode]
var lastReads, potLastReads: IntSet
var pc = 0
collectLastReads(c.g, cache, alreadySeen, lastReads, potLastReads, pc, c.g.len)
collectLastReads(c.g, cache, lastReads, potLastReads, pc, c.g.len)
lastReads.incl potLastReads
var lastReadTable: Table[PNode, seq[int]]
for position, node in c.g:
@ -1102,6 +1120,10 @@ proc injectDestructorCalls*(g: ModuleGraph; idgen: IdGenerator; owner: PSym; n:
if allPositionsLastRead:
node.flags.incl nfLastRead
var alreadySeen: HashSet[PNode]
pc = 0
collectFirstWrites(c.g, alreadySeen, pc, c.g.len)
var scope: Scope
let body = p(n, c, scope, normal)