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#
#
# The Nim Compiler
# (c) Copyright 2012 Andreas Rumpf
#
# See the file "copying.txt", included in this
# distribution, for details about the copyright.
#
## Simple alias analysis for the HLO and the code generators.
import
ast, astalgo, types, trees, intsets, msgs
type
TAnalysisResult* = enum
arNo, arMaybe, arYes
proc isPartOfAux(a, b: PType, marker: var IntSet): TAnalysisResult
proc isPartOfAux(n: PNode, b: PType, marker: var IntSet): TAnalysisResult =
result = arNo
case n.kind
of nkRecList:
for i in countup(0, sonsLen(n) - 1):
result = isPartOfAux(n.sons[i], b, marker)
if result == arYes: return
of nkRecCase:
assert(n.sons[0].kind == nkSym)
result = isPartOfAux(n.sons[0], b, marker)
if result == arYes: return
for i in countup(1, sonsLen(n) - 1):
case n.sons[i].kind
of nkOfBranch, nkElse:
result = isPartOfAux(lastSon(n.sons[i]), b, marker)
if result == arYes: return
else: internalError("isPartOfAux(record case branch)")
of nkSym:
result = isPartOfAux(n.sym.typ, b, marker)
else: internalError(n.info, "isPartOfAux()")
proc isPartOfAux(a, b: PType, marker: var IntSet): TAnalysisResult =
result = arNo
if a == nil or b == nil: return
if containsOrIncl(marker, a.id): return
if compareTypes(a, b, dcEqIgnoreDistinct): return arYes
case a.kind
of tyObject:
if a.sons[0] != nil:
result = isPartOfAux(a.sons[0].skipTypes(skipPtrs), b, marker)
if result == arNo: result = isPartOfAux(a.n, b, marker)
of tyGenericInst, tyDistinct:
result = isPartOfAux(lastSon(a), b, marker)
of tyArray, tyArrayConstr, tySet, tyTuple:
for i in countup(0, sonsLen(a) - 1):
result = isPartOfAux(a.sons[i], b, marker)
if result == arYes: return
else: discard
proc isPartOf(a, b: PType): TAnalysisResult =
## checks iff 'a' can be part of 'b'. Iterates over VALUE types!
var marker = initIntSet()
# watch out: parameters reversed because I'm too lazy to change the code...
result = isPartOfAux(b, a, marker)
proc isPartOf*(a, b: PNode): TAnalysisResult =
## checks if location `a` can be part of location `b`. We treat seqs and
## strings as pointers because the code gen often just passes them as such.
##
## Note: `a` can only be part of `b`, if `a`'s type can be part of `b`'s
## type. Since however type analysis is more expensive, we perform it only
## if necessary.
##
## cases:
##
## YES-cases:
## x <| x # for general trees
## x[] <| x
## x[i] <| x
## x.f <| x
##
## NO-cases:
## x !<| y # depending on type and symbol kind
## x[constA] !<| x[constB]
## x.f !<| x.g
## x.f !<| y.f iff x !<= y
##
## MAYBE-cases:
##
## x[] ?<| y[] iff compatible type
##
##
## x[] ?<| y depending on type
##
if a.kind == b.kind:
case a.kind
of nkSym:
const varKinds = {skVar, skTemp, skProc}
# same symbol: aliasing:
if a.sym.id == b.sym.id: result = arYes
elif a.sym.kind in varKinds or b.sym.kind in varKinds:
# actually, a param could alias a var but we know that cannot happen
# here. XXX make this more generic
result = arNo
else:
# use expensive type check:
if isPartOf(a.sym.typ, b.sym.typ) != arNo:
result = arMaybe
of nkBracketExpr:
result = isPartOf(a[0], b[0])
if len(a) >= 2 and len(b) >= 2:
# array accesses:
if result == arYes and isDeepConstExpr(a[1]) and isDeepConstExpr(b[1]):
# we know it's the same array and we have 2 constant indexes;
# if they are
var x = if a[1].kind == nkHiddenStdConv: a[1][1] else: a[1]
var y = if b[1].kind == nkHiddenStdConv: b[1][1] else: b[1]
if sameValue(x, y): result = arYes
else: result = arNo
# else: maybe and no are accurate
else:
# pointer derefs:
if result != arYes:
if isPartOf(a.typ, b.typ) != arNo: result = arMaybe
of nkDotExpr:
result = isPartOf(a[0], b[0])
if result != arNo:
# if the fields are different, it's not the same location
if a[1].sym.id != b[1].sym.id:
result = arNo
of nkHiddenDeref, nkDerefExpr:
result = isPartOf(a[0], b[0])
# weaken because of indirection:
if result != arYes:
if isPartOf(a.typ, b.typ) != arNo: result = arMaybe
of nkHiddenStdConv, nkHiddenSubConv, nkConv:
result = isPartOf(a[1], b[1])
of nkObjUpConv, nkObjDownConv, nkCheckedFieldExpr:
result = isPartOf(a[0], b[0])
else: discard
# Calls return a new location, so a default of ``arNo`` is fine.
else:
# go down recursively; this is quite demanding:
const
Ix0Kinds = {nkDotExpr, nkBracketExpr, nkObjUpConv, nkObjDownConv,
nkCheckedFieldExpr, nkHiddenAddr}
Ix1Kinds = {nkHiddenStdConv, nkHiddenSubConv, nkConv}
DerefKinds = {nkHiddenDeref, nkDerefExpr}
case b.kind
of Ix0Kinds:
# a* !<| b.f iff a* !<| b
result = isPartOf(a, b[0])
of DerefKinds:
# a* !<| b[] iff
if isPartOf(a.typ, b.typ) != arNo:
result = isPartOf(a, b[0])
if result == arNo: result = arMaybe
of Ix1Kinds:
# a* !<| T(b) iff a* !<| b
result = isPartOf(a, b[1])
of nkSym:
# b is an atom, so we have to check a:
case a.kind
of Ix0Kinds:
# a.f !<| b* iff a.f !<| b*
result = isPartOf(a[0], b)
of Ix1Kinds:
result = isPartOf(a[1], b)
of DerefKinds:
if isPartOf(a.typ, b.typ) != arNo:
result = isPartOf(a[0], b)
if result == arNo: result = arMaybe
else: discard
else: discard
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