--exception:goto switch for deterministic exception handling (#12977)
This implements "deterministic" exception handling for Nim based on goto instead of setjmp. This means raising an exception is much cheaper than in C++'s table based implementations. Supports hard realtime systems. Default for --gc:arc and the C target because it's generally a good idea and arc is all about deterministic behavior. Note: This implies that fatal runtime traps are not catchable anymore! This needs to be documented.
This commit is contained in:
Andreas Rumpf
GitHub
parent
8a63caca07
commit
c3344862b0
23 changed files with 640 additions and 183 deletions
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@ -196,13 +196,13 @@ proc genState(p: BProc, n: PNode) =
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proc blockLeaveActions(p: BProc, howManyTrys, howManyExcepts: int) =
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# Called by return and break stmts.
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# Deals with issues faced when jumping out of try/except/finally stmts,
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# Deals with issues faced when jumping out of try/except/finally stmts.
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var stack = newSeq[tuple[fin: PNode, inExcept: bool]](0)
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var stack = newSeq[tuple[fin: PNode, inExcept: bool, label: Natural]](0)
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for i in 1..howManyTrys:
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let tryStmt = p.nestedTryStmts.pop
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if not p.module.compileToCpp or optNoCppExceptions in p.config.globalOptions:
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if p.config.exc == excSetjmp:
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# Pop safe points generated by try
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if not tryStmt.inExcept:
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linefmt(p, cpsStmts, "#popSafePoint();$n", [])
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@ -221,10 +221,10 @@ proc blockLeaveActions(p: BProc, howManyTrys, howManyExcepts: int) =
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for i in countdown(howManyTrys-1, 0):
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p.nestedTryStmts.add(stack[i])
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if not p.module.compileToCpp or optNoCppExceptions in p.config.globalOptions:
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if p.config.exc != excCpp:
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# Pop exceptions that was handled by the
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# except-blocks we are in
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if not p.noSafePoints:
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if noSafePoints notin p.flags:
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for i in countdown(howManyExcepts-1, 0):
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linefmt(p, cpsStmts, "#popCurrentException();$n", [])
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@ -237,7 +237,7 @@ proc genGotoState(p: BProc, n: PNode) =
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var a: TLoc
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initLocExpr(p, n[0], a)
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lineF(p, cpsStmts, "switch ($1) {$n", [rdLoc(a)])
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p.beforeRetNeeded = true
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p.flags.incl beforeRetNeeded
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lineF(p, cpsStmts, "case -1:$n", [])
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blockLeaveActions(p,
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howManyTrys = p.nestedTryStmts.len,
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@ -454,13 +454,13 @@ proc genIf(p: BProc, n: PNode, d: var TLoc) =
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proc genReturnStmt(p: BProc, t: PNode) =
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if nfPreventCg in t.flags: return
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p.beforeRetNeeded = true
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p.flags.incl beforeRetNeeded
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genLineDir(p, t)
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if (t[0].kind != nkEmpty): genStmts(p, t[0])
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blockLeaveActions(p,
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howManyTrys = p.nestedTryStmts.len,
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howManyExcepts = p.inExceptBlockLen)
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if (p.finallySafePoints.len > 0) and not p.noSafePoints:
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if (p.finallySafePoints.len > 0) and noSafePoints notin p.flags:
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# If we're in a finally block, and we came here by exception
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# consume it before we return.
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var safePoint = p.finallySafePoints[^1]
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@ -687,15 +687,27 @@ proc genBreakStmt(p: BProc, t: PNode) =
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genLineDir(p, t)
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lineF(p, cpsStmts, "goto $1;$n", [label])
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proc raiseExit(p: BProc) =
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assert p.config.exc == excGoto
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p.flags.incl nimErrorFlagAccessed
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if p.nestedTryStmts.len == 0:
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p.flags.incl beforeRetNeeded
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# easy case, simply goto 'ret':
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lineCg(p, cpsStmts, "if (NIM_UNLIKELY(*nimErr_)) goto BeforeRet_;$n", [])
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else:
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lineCg(p, cpsStmts, "if (NIM_UNLIKELY(*nimErr_)) goto LA$1_;$n",
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[p.nestedTryStmts[^1].label])
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proc genRaiseStmt(p: BProc, t: PNode) =
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if p.module.compileToCpp:
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discard cgsym(p.module, "popCurrentExceptionEx")
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if p.nestedTryStmts.len > 0 and p.nestedTryStmts[^1].inExcept:
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# if the current try stmt have a finally block,
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# we must execute it before reraising
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let finallyBlock = p.nestedTryStmts[^1].fin
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if finallyBlock != nil:
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genSimpleBlock(p, finallyBlock[0])
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if p.config.exc != excGoto:
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if p.config.exc == excCpp:
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discard cgsym(p.module, "popCurrentExceptionEx")
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if p.nestedTryStmts.len > 0 and p.nestedTryStmts[^1].inExcept:
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# if the current try stmt have a finally block,
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# we must execute it before reraising
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let finallyBlock = p.nestedTryStmts[^1].fin
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if finallyBlock != nil:
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genSimpleBlock(p, finallyBlock[0])
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if t[0].kind != nkEmpty:
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var a: TLoc
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initLocExprSingleUse(p, t[0], a)
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@ -714,10 +726,22 @@ proc genRaiseStmt(p: BProc, t: PNode) =
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else:
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genLineDir(p, t)
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# reraise the last exception:
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if p.module.compileToCpp and optNoCppExceptions notin p.config.globalOptions:
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if p.config.exc == excCpp:
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line(p, cpsStmts, ~"throw;$n")
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else:
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linefmt(p, cpsStmts, "#reraiseException();$n", [])
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if p.config.exc == excGoto:
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let L = p.nestedTryStmts.len
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if L == 0:
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p.flags.incl beforeRetNeeded
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# easy case, simply goto 'ret':
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lineCg(p, cpsStmts, "goto BeforeRet_;$n", [])
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else:
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# raise inside an 'except' must go to the finally block,
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# raise outside an 'except' block must go to the 'except' list.
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lineCg(p, cpsStmts, "goto LA$1_;$n",
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[p.nestedTryStmts[L-1].label])
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# + ord(p.nestedTryStmts[L-1].inExcept)])
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template genCaseGenericBranch(p: BProc, b: PNode, e: TLoc,
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rangeFormat, eqFormat: FormatStr, labl: TLabel) =
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@ -906,8 +930,8 @@ proc genCase(p: BProc, t: PNode, d: var TLoc) =
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proc genRestoreFrameAfterException(p: BProc) =
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if optStackTrace in p.module.config.options:
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if not p.hasCurFramePointer:
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p.hasCurFramePointer = true
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if hasCurFramePointer notin p.flags:
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p.flags.incl hasCurFramePointer
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p.procSec(cpsLocals).add(ropecg(p.module, "\tTFrame* _nimCurFrame;$n", []))
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p.procSec(cpsInit).add(ropecg(p.module, "\t_nimCurFrame = #getFrame();$n", []))
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linefmt(p, cpsStmts, "#setFrame(_nimCurFrame);$n", [])
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@ -938,7 +962,7 @@ proc genTryCpp(p: BProc, t: PNode, d: var TLoc) =
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genLineDir(p, t)
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discard cgsym(p.module, "popCurrentExceptionEx")
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let fin = if t[^1].kind == nkFinally: t[^1] else: nil
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p.nestedTryStmts.add((fin, false))
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p.nestedTryStmts.add((fin, false, 0.Natural))
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startBlock(p, "try {$n")
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expr(p, t[0], d)
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endBlock(p)
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@ -982,7 +1006,116 @@ proc genTryCpp(p: BProc, t: PNode, d: var TLoc) =
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genSimpleBlock(p, t[^1][0])
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proc genTry(p: BProc, t: PNode, d: var TLoc) =
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proc bodyCanRaise(n: PNode): bool =
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case n.kind
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of nkCallKinds:
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result = canRaise(n[0])
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if not result:
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# also check the arguments:
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for i in 1 ..< n.len:
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if bodyCanRaise(n[i]): return true
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of nkRaiseStmt:
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result = true
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of nkTypeSection, nkProcDef, nkConverterDef, nkMethodDef, nkIteratorDef,
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nkMacroDef, nkTemplateDef, nkLambda, nkDo, nkFuncDef:
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result = false
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else:
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for i in 0 ..< safeLen(n):
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if bodyCanRaise(n[i]): return true
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result = false
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proc genTryGoto(p: BProc; t: PNode; d: var TLoc) =
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if not bodyCanRaise(t):
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# optimize away the 'try' block:
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expr(p, t[0], d)
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if t.len > 1 and t[^1].kind == nkFinally:
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genStmts(p, t[^1][0])
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return
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let fin = if t[^1].kind == nkFinally: t[^1] else: nil
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inc p.labels, 2
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let lab = p.labels-1
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p.nestedTryStmts.add((fin, false, Natural lab))
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p.flags.incl nimErrorFlagAccessed
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linefmt(p, cpsStmts, "NI oldNimErr$1_ = *nimErr_; *nimErr_ = 0;;$n", [lab])
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expr(p, t[0], d)
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if 1 < t.len and t[1].kind == nkExceptBranch:
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startBlock(p, "if (NIM_UNLIKELY(*nimErr_)) {$n")
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else:
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startBlock(p)
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# pretend we did handle the error for the safe execution of the sections:
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linefmt(p, cpsStmts, "LA$1_: oldNimErr$1_ = *nimErr_; *nimErr_ = 0;$n", [lab])
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p.nestedTryStmts[^1].inExcept = true
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var i = 1
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while (i < t.len) and (t[i].kind == nkExceptBranch):
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inc p.labels
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let nextExcept = p.labels
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p.nestedTryStmts[^1].label = nextExcept
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# bug #4230: avoid false sharing between branches:
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if d.k == locTemp and isEmptyType(t.typ): d.k = locNone
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if t[i].len == 1:
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# general except section:
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if i > 1: lineF(p, cpsStmts, "else", [])
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startBlock(p)
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# we handled the exception, remember this:
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linefmt(p, cpsStmts, "--oldNimErr$1_;$n", [lab])
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expr(p, t[i][0], d)
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else:
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var orExpr: Rope = nil
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for j in 0..<t[i].len - 1:
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assert(t[i][j].kind == nkType)
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if orExpr != nil: orExpr.add("||")
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let checkFor = if optTinyRtti in p.config.globalOptions:
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genTypeInfo2Name(p.module, t[i][j].typ)
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else:
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genTypeInfo(p.module, t[i][j].typ, t[i][j].info)
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let memberName = if p.module.compileToCpp: "m_type" else: "Sup.m_type"
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appcg(p.module, orExpr, "#isObj(#nimBorrowCurrentException()->$1, $2)", [memberName, checkFor])
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if i > 1: line(p, cpsStmts, "else ")
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startBlock(p, "if ($1) {$n", [orExpr])
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# we handled the exception, remember this:
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linefmt(p, cpsStmts, "--oldNimErr$1_;$n", [lab])
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expr(p, t[i][^1], d)
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linefmt(p, cpsStmts, "#popCurrentException();$n", [])
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linefmt(p, cpsStmts, "LA$1_:;$n", [nextExcept])
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endBlock(p)
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inc(i)
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discard pop(p.nestedTryStmts)
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endBlock(p)
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#linefmt(p, cpsStmts, "LA$1_:;$n", [lab+1])
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if i < t.len and t[i].kind == nkFinally:
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startBlock(p)
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if not bodyCanRaise(t[i][0]):
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# this is an important optimization; most destroy blocks are detected not to raise an
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# exception and so we help the C optimizer by not mutating nimErr_ pointlessly:
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genStmts(p, t[i][0])
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else:
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# pretend we did handle the error for the safe execution of the 'finally' section:
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linefmt(p, cpsStmts, "NI oldNimErrFin$1_ = *nimErr_; *nimErr_ = 0;$n", [lab])
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genStmts(p, t[i][0])
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# this is correct for all these cases:
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# 1. finally is run during ordinary control flow
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# 2. finally is run after 'except' block handling: these however set the
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# error back to nil.
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# 3. finally is run for exception handling code without any 'except'
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# handler present or only handlers that did not match.
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linefmt(p, cpsStmts, "*nimErr_ += oldNimErr$1_ + (*nimErr_ - oldNimErrFin$1_); oldNimErr$1_ = 0;$n", [lab])
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raiseExit(p)
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endBlock(p)
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# restore the real error value:
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linefmt(p, cpsStmts, "*nimErr_ += oldNimErr$1_;$n", [lab])
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proc genTrySetjmp(p: BProc, t: PNode, d: var TLoc) =
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# code to generate:
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#
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# XXX: There should be a standard dispatch algorithm
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@ -1013,12 +1146,12 @@ proc genTry(p: BProc, t: PNode, d: var TLoc) =
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#
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if not isEmptyType(t.typ) and d.k == locNone:
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getTemp(p, t.typ, d)
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let quirkyExceptions = isDefined(p.config, "nimQuirky") or
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let quirkyExceptions = p.config.exc == excQuirky or
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(t.kind == nkHiddenTryStmt and sfSystemModule in p.module.module.flags)
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if not quirkyExceptions:
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p.module.includeHeader("<setjmp.h>")
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else:
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p.noSafePoints = true
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p.flags.incl noSafePoints
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genLineDir(p, t)
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discard cgsym(p.module, "Exception")
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var safePoint: Rope
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@ -1036,7 +1169,7 @@ proc genTry(p: BProc, t: PNode, d: var TLoc) =
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linefmt(p, cpsStmts, "$1.status = setjmp($1.context);$n", [safePoint])
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startBlock(p, "if ($1.status == 0) {$n", [safePoint])
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let fin = if t[^1].kind == nkFinally: t[^1] else: nil
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p.nestedTryStmts.add((fin, quirkyExceptions))
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p.nestedTryStmts.add((fin, quirkyExceptions, 0.Natural))
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expr(p, t[0], d)
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if not quirkyExceptions:
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linefmt(p, cpsStmts, "#popSafePoint();$n", [])
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