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90 lines
2.6 KiB
Nim
90 lines
2.6 KiB
Nim
#
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#
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# The Nim Compiler
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# (c) Copyright 2015 Andreas Rumpf
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#
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# See the file "copying.txt", included in this
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# distribution, for details about the copyright.
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#
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## This module implements for loop detection for better C code generation.
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import ast, astalgo
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const
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someCmp = {mEqI, mEqF64, mEqEnum, mEqCh, mEqB, mEqRef, mEqProc,
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mLeI, mLeF64, mLeU, mLeEnum,
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mLeCh, mLeB, mLePtr, mLtI, mLtF64, mLtU, mLtEnum,
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mLtCh, mLtB, mLtPtr}
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proc isCounter(s: PSym): bool {.inline.} =
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s.kind in {skResult, skVar, skLet, skTemp} and
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{sfGlobal, sfAddrTaken} * s.flags == {}
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proc isCall(n: PNode): bool {.inline.} =
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n.kind in nkCallKinds and n[0].kind == nkSym
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proc fromSystem(op: PSym): bool = sfSystemModule in getModule(op).flags
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proc getCounter(lastStmt: PNode): PSym =
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if lastStmt.isCall:
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let op = lastStmt.sym
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if op.magic in {mDec, mInc} or
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((op.name.s == "+=" or op.name.s == "-=") and op.fromSystem):
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if op[1].kind == nkSym and isCounter(op[1].sym):
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result = op[1].sym
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proc counterInTree(n, loop: PNode; counter: PSym): bool =
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# prune the search tree: within the loop the counter may be used:
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if n == loop: return
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case n.kind
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of nkSym:
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if n.sym == counter: return true
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of nkVarSection, nkLetSection:
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# definitions are fine!
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for it in n:
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if counterInTree(it.lastSon): return true
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else:
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for i in 0..<n.safeLen:
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if counterInTree(n[i], loop, counter): return true
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proc copyExcept(n: PNode, x, dest: PNode) =
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if x == n: return
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if n.kind in {nkStmtList, nkStmtListExpr}:
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for i in 0..<n.len: copyExcept(n[i], x, dest)
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else:
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dest.add n
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type
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ForLoop* = object
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counter*: PSym
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init*, cond*, increment*, body*: PNode
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proc extractForLoop*(loop, fullTree: PNode): ForLoop =
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## returns 'counter == nil' if the while loop 'n' is not a for loop:
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assert loop.kind == nkWhileStmt
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let cond == loop[0]
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if not cond.isCall: return
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if cond[0].sym.magic notin someCmp: return
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var lastStmt = loop[1]
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while lastStmt.kind in {nkStmtList, nkStmtListExpr}:
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lastStmt = lastStmt.lastSon
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let counter = getCounter(lastStmt)
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if counter.isNil or counter.ast.isNil: return
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template `=~`(a, b): expr = a.kind == nkSym and a.sym == b
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if cond[1] =~ counter or cond[2] =~ counter:
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# ok, now check 'counter' is not used *after* the loop
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if counterInTree(fullTree, loop, counter): return
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# ok, success, fill in the fields:
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result.counter = counter
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result.init = counter.ast
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result.cond = cond
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result.increment = lastStmt
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result.body = newNodeI(nkStmtList, loop[1].info)
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copyExcept(loop[1], lastStmt, result.body)
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