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DFA attempt to capture the essence of linear types

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This commit is contained in:
Andreas Rumpf 2017-12-23 19:50:15 +01:00
commit 8e7829ff82
1 changed files with 21 additions and 2 deletions
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compiler/dfa.nim
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@ -337,10 +337,12 @@ proc gen(c: var Con; n: PNode) =
proc dfa(code: seq[Instr]) = proc dfa(code: seq[Instr]) =
var u = newSeq[IntSet](code.len) # usages var u = newSeq[IntSet](code.len) # usages
var d = newSeq[IntSet](code.len) # defs var d = newSeq[IntSet](code.len) # defs
var c = newSeq[IntSet](code.len) # consumed
var backrefs = initTable[int, int]() var backrefs = initTable[int, int]()
for i in 0..<code.len: for i in 0..<code.len:
u[i] = initIntSet() u[i] = initIntSet()
d[i] = initIntSet() d[i] = initIntSet()
c[i] = initIntSet()
case code[i].kind case code[i].kind
of use, useWithinCall: u[i].incl(code[i].sym.id) of use, useWithinCall: u[i].incl(code[i].sym.id)
of def: d[i].incl(code[i].sym.id) of def: d[i].incl(code[i].sym.id)
@ -352,6 +354,7 @@ proc dfa(code: seq[Instr]) =
var maxIters = 50 var maxIters = 50
var someChange = true var someChange = true
var takenGotos = initIntSet() var takenGotos = initIntSet()
var consuming = -1
while w.len > 0 and maxIters > 0: # and someChange: while w.len > 0 and maxIters > 0: # and someChange:
dec maxIters dec maxIters
var pc = w.pop() # w[^1] var pc = w.pop() # w[^1]
@ -389,6 +392,10 @@ proc dfa(code: seq[Instr]) =
when defined(debugDfa): when defined(debugDfa):
echo "Excluding ", pc, " prev ", prevPc echo "Excluding ", pc, " prev ", prevPc
assign d[pc], intersect assign d[pc], intersect
if consuming >= 0:
if not c[pc].containsOrIncl(consuming):
someChange = true
consuming = -1
# our interpretation ![I!]: # our interpretation ![I!]:
prevPc = pc prevPc = pc
@ -406,12 +413,21 @@ proc dfa(code: seq[Instr]) =
#if someChange: #if someChange:
w.add pc + code[pc].dest w.add pc + code[pc].dest
inc pc inc pc
of use, useWithinCall, def: of use, useWithinCall:
#if not d[prevPc].missingOrExcl():
# someChange = true
consuming = code[pc].sym.id
when defined(debugDfa):
echo "consumed: ", consuming
inc pc
of def:
if not d[pc].containsOrIncl(code[pc].sym.id):
someChange = true
inc pc inc pc
when defined(useDfa) and defined(debugDfa): when defined(useDfa) and defined(debugDfa):
for i in 0..<code.len: for i in 0..<code.len:
echo "PC ", i, ": defs: ", d[i], "; uses ", u[i] echo "PC ", i, ": defs: ", d[i], "; uses ", u[i], "; consumes ", c[i]
# now check the condition we're interested in: # now check the condition we're interested in:
for i in 0..<code.len: for i in 0..<code.len:
@ -419,6 +435,9 @@ proc dfa(code: seq[Instr]) =
of use, useWithinCall: of use, useWithinCall:
if code[i].sym.id notin d[i]: if code[i].sym.id notin d[i]:
localError(code[i].n.info, "usage of an uninitialized variable") localError(code[i].n.info, "usage of an uninitialized variable")
if code[i].sym.id in c[i]:
localError(code[i].n.info, "usage of an already consumed variable")
else: discard else: discard
proc dfaUnused(code: seq[Instr]) = proc dfaUnused(code: seq[Instr]) =