tools/ccc/ccclib/Driver.py

import os
import platform
import sys
import tempfile
from pprint import pprint

###

import Arguments
import Jobs
import HostInfo
import Phases
import Tools
import Types
import Util

# FIXME: Clean up naming of options and arguments. Decide whether to
# rename Option and be consistent about use of Option/Arg.

####

class Driver(object):
    def __init__(self, driverName, driverDir):
        self.driverName = driverName
        self.driverDir = driverDir
        self.hostInfo = None
        self.parser = Arguments.OptionParser()
        self.cccHostBits = self.cccHostMachine = None
        self.cccHostSystem = self.cccHostRelease = None
        self.cccCXX = False
        self.cccClang = False
        self.cccEcho = False
        self.cccFallback = False

    # Host queries which can be forcibly over-riden by the user for
    # testing purposes.
    #
    # FIXME: We should make sure these are drawn from a fixed set so
    # that nothing downstream ever plays a guessing game.

    def getHostBits(self):
        if self.cccHostBits:
            return self.cccHostBits
        
        return platform.architecture()[0].replace('bit','')

    def getHostMachine(self):
        if self.cccHostMachine:
            return self.cccHostMachine

        machine = platform.machine()
        # Normalize names.
        if machine == 'Power Macintosh':
            return 'ppc'
        return machine

    def getHostSystemName(self):
        if self.cccHostSystem:
            return self.cccHostSystem
        
        return platform.system().lower()

    def getHostReleaseName(self):
        if self.cccHostRelease:
            return self.cccHostRelease
        
        return platform.release()

    def getenvBool(self, name):
        var = os.getenv(name)
        if not var:
            return False

        try:
            return bool(int(var))
        except:
            return False

    ###

    def run(self, argv):
        # FIXME: Things to support from environment: GCC_EXEC_PREFIX,
        # COMPILER_PATH, LIBRARY_PATH, LPATH, CC_PRINT_OPTIONS,
        # QA_OVERRIDE_GCC3_OPTIONS, ...?

        # FIXME: -V and -b processing

        # Handle some special -ccc- options used for testing which are
        # only allowed at the beginning of the command line.
        cccPrintOptions = False
        cccPrintPhases = False

        # FIXME: How to handle override of host? ccc specific options?
        # Abuse -b?
        if self.getenvBool('CCC_CLANG'):
            self.cccClang = True
        if self.getenvBool('CCC_ECHO'):
            self.cccEcho = True
        if self.getenvBool('CCC_FALLBACK'):
            self.cccFallback = True

        while argv and argv[0].startswith('-ccc-'):
            fullOpt,argv = argv[0],argv[1:]
            opt = fullOpt[5:]

            if opt == 'print-options':
                cccPrintOptions = True
            elif opt == 'print-phases':
                cccPrintPhases = True
            elif opt == 'cxx':
                self.cccCXX = True
            elif opt == 'clang':
                self.cccClang = True
            elif opt == 'echo':
                self.cccEcho = True
            elif opt == 'fallback':
                self.cccFallback = True
            elif opt == 'host-bits':
                self.cccHostBits,argv = argv[0],argv[1:]
            elif opt == 'host-machine':
                self.cccHostMachine,argv = argv[0],argv[1:]
            elif opt == 'host-system':
                self.cccHostSystem,argv = argv[0],argv[1:]
            elif opt == 'host-release':
                self.cccHostRelease,argv = argv[0],argv[1:]
            else:
                raise Arguments.InvalidArgumentsError("invalid option: %r" % fullOpt)

        self.hostInfo = HostInfo.getHostInfo(self)
        self.toolChain = self.hostInfo.getToolChain()
        
        args = self.parser.parseArgs(argv)

        # FIXME: Ho hum I have just realized -Xarch_ is broken. We really
        # need to reparse the Arguments after they have been expanded by
        # -Xarch. How is this going to work?
        #
        # Scratch that, we aren't going to do that; it really disrupts the
        # organization, doesn't consistently work with gcc-dd, and is
        # confusing. Instead we are going to enforce that -Xarch_ is only
        # used with options which do not alter the driver behavior. Let's
        # hope this is ok, because the current architecture is a little
        # tied to it.

        if cccPrintOptions:
            self.printOptions(args)
            sys.exit(0)

        self.handleImmediateOptions(args)

        if self.hostInfo.useDriverDriver():
            phases = self.buildPipeline(args)
        else:
            phases = self.buildNormalPipeline(args)

        if cccPrintPhases:
            self.printPhases(phases, args)
            sys.exit(0)
            
        if 0:
            print Util.pprint(phases)

        jobs = self.bindPhases(phases, args)

        # FIXME: We should provide some basic sanity checking of the
        # pipeline as a "verification" sort of stage. For example, the
        # pipeline should never end up writing to an output file in two
        # places (I think). The pipeline should also never end up writing
        # to an output file that is an input.
        #
        # This is intended to just be a "verify" step, not a functionality
        # step. It should catch things like the driver driver not
        # preventing -save-temps, but it shouldn't change behavior (so we
        # can turn it off in Release-Asserts builds).

        # Print in -### syntax.
        hasHashHashHash = args.getLastArg(self.parser.hashHashHashOption)
        if hasHashHashHash:
            self.claim(hasHashHashHash)
            for j in jobs.iterjobs():
                if isinstance(j, Jobs.Command):
                    print >>sys.stderr, ' "%s"' % '" "'.join(j.getArgv())
                elif isinstance(j, Jobs.PipedJob):
                    for c in j.commands:
                        print >>sys.stderr, ' "%s" %c' % ('" "'.join(c.getArgv()),
                                                          "| "[c is j.commands[-1]])
                elif not isinstance(j, JobList):
                    raise ValueError,'Encountered unknown job.'
            sys.exit(0)

        for j in jobs.iterjobs():
            if isinstance(j, Jobs.Command):
                if self.cccEcho:
                    print >>sys.stderr, ' '.join(map(repr,j.getArgv()))
                    sys.stderr.flush()
                res = os.spawnvp(os.P_WAIT, j.executable, j.getArgv())
                if res:
                    sys.exit(res)
            elif isinstance(j, Jobs.PipedJob):
                import subprocess
                procs = []
                for sj in j.commands:
                    if self.cccEcho:
                        print >> sys.stderr, ' '.join(map(repr,sj.getArgv()))
                        sys.stdout.flush()

                    if not procs:
                        stdin = None
                    else:
                        stdin = procs[-1].stdout
                    if sj is j.commands[-1]:
                        stdout = None
                    else:
                        stdout = subprocess.PIPE
                    procs.append(subprocess.Popen(sj.getArgv(), 
                                                  executable=sj.executable,
                                                  stdin=stdin,
                                                  stdout=stdout))
                for proc in procs:
                    res = proc.wait()
                    if res:
                        sys.exit(res)
            else:
                raise ValueError,'Encountered unknown job.'

    def claim(self, option):
        # FIXME: Move to OptionList once introduced and implement.
        pass

    def warning(self, message):
        print >>sys.stderr,'%s: %s' % (self.driverName, message)

    def printOptions(self, args):
        for i,arg in enumerate(args):
            if isinstance(arg, Arguments.MultipleValuesArg):
                values = list(args.getValues(arg))
            elif isinstance(arg, Arguments.ValueArg):
                values = [args.getValue(arg)]
            elif isinstance(arg, Arguments.JoinedAndSeparateValuesArg):
                values = [args.getJoinedValue(arg), args.getSeparateValue(arg)]
            else:
                values = []
            print 'Option %d - Name: "%s", Values: {%s}' % (i, arg.opt.name, 
                                                            ', '.join(['"%s"' % v 
                                                                       for v in values]))

    def printPhases(self, phases, args):
        def printPhase(p, f, steps, arch=None):
            if p in steps:
                return steps[p]
            elif isinstance(p, Phases.BindArchAction):
                for kid in p.inputs:
                    printPhase(kid, f, steps, p.arch)
                steps[p] = len(steps)
                return

            if isinstance(p, Phases.InputAction):
                phaseName = 'input'
                inputStr = '"%s"' % args.getValue(p.filename)
            else:
                phaseName = p.phase.name
                inputs = [printPhase(i, f, steps, arch) 
                          for i in p.inputs]
                inputStr = '{%s}' % ', '.join(map(str, inputs))
            if arch is not None:
                phaseName += '-' + args.getValue(arch)
            steps[p] = index = len(steps)
            print "%d: %s, %s, %s" % (index,phaseName,inputStr,p.type.name)
            return index
        steps = {}
        for phase in phases:
            printPhase(phase, sys.stdout, steps)

    def handleImmediateOptions(self, args):
        # FIXME: Some driver Arguments are consumed right off the bat,
        # like -dumpversion. Currently the gcc-dd handles these
        # poorly, so we should be ok handling them upfront instead of
        # after driver-driver level dispatching.
        #
        # FIXME: The actual order of these options in gcc is all over the
        # place. The -dump ones seem to be first and in specification
        # order, but there are other levels of precedence. For example,
        # -print-search-dirs is evaluated before -print-prog-name=,
        # regardless of order (and the last instance of -print-prog-name=
        # wins verse itself).
        #
        # FIXME: Do we want to report "argument unused" type errors in the
        # presence of things like -dumpmachine and -print-search-dirs?
        # Probably not.
        arg = args.getLastArg(self.parser.dumpmachineOption)
        if arg:
            print 'FIXME: %s' % arg.opt.name
            sys.exit(1)

        arg = args.getLastArg(self.parser.dumpspecsOption)
        if arg:
            print 'FIXME: %s' % arg.opt.name
            sys.exit(1)

        arg = args.getLastArg(self.parser.dumpversionOption)
        if arg:
            print 'FIXME: %s' % arg.opt.name
            sys.exit(1)

        arg = args.getLastArg(self.parser.printFileNameOption)
        if arg:
            print 'FIXME: %s' % arg.opt.name
            sys.exit(1)

        arg = args.getLastArg(self.parser.printMultiDirectoryOption)
        if arg:
            print 'FIXME: %s' % arg.opt.name
            sys.exit(1)

        arg = args.getLastArg(self.parser.printMultiLibOption)
        if arg:
            print 'FIXME: %s' % arg.opt.name
            sys.exit(1)

        arg = args.getLastArg(self.parser.printProgNameOption)
        if arg:
            print 'FIXME: %s' % arg.opt.name
            sys.exit(1)

        arg = args.getLastArg(self.parser.printLibgccFilenameOption)
        if arg:
            print 'FIXME: %s' % arg.opt.name
            sys.exit(1)

        arg = args.getLastArg(self.parser.printSearchDirsOption)
        if arg:
            print 'FIXME: %s' % arg.opt.name
            sys.exit(1)

    def buildNormalPipeline(self, args):
        hasCombine = args.getLastArg(self.parser.combineOption)
        hasSyntaxOnly = args.getLastArg(self.parser.syntaxOnlyOption)
        hasDashC = args.getLastArg(self.parser.cOption)
        hasDashE = args.getLastArg(self.parser.EOption)
        hasDashS = args.getLastArg(self.parser.SOption)
        hasDashM = args.getLastArg(self.parser.MOption)
        hasDashMM = args.getLastArg(self.parser.MMOption)

        inputType = None
        inputTypeOpt = None
        inputs = []
        for a in args:
            if a.opt is self.parser.inputOption:
                inputValue = args.getValue(a)
                if inputType is None:
                    base,ext = os.path.splitext(inputValue)
                    if ext and ext in Types.kTypeSuffixMap:
                        klass = Types.kTypeSuffixMap[ext]
                    else:
                        # FIXME: Its not clear why we shouldn't just
                        # revert to unknown. I think this is more likely a
                        # bug / unintended behavior in gcc. Not very
                        # important though.
                        klass = Types.ObjectType
                else:
                    assert inputTypeOpt is not None
                    self.claim(inputTypeOpt)
                    klass = inputType

                # Check that the file exists. It isn't clear this is
                # worth doing, since the tool presumably does this
                # anyway, and this just adds an extra stat to the
                # equation, but this is gcc compatible.
                if not os.path.exists(inputValue):
                    self.warning("%s: No such file or directory" % inputValue)
                else:
                    inputs.append((klass, a))
            elif a.opt.isLinkerInput:
                # Treat as a linker input.
                #
                # FIXME: This might not be good enough. We may
                # need to introduce another type for this case, so
                # that other code which needs to know the inputs
                # handles this properly. Best not to try and lipo
                # this, for example.
                inputs.append((Types.ObjectType, a))
            elif a.opt is self.parser.xOption:
                inputTypeOpt = a
                value = args.getValue(a)
                if value in Types.kTypeSpecifierMap:
                    inputType = Types.kTypeSpecifierMap[value]
                else:
                    # FIXME: How are we going to handle diagnostics.
                    self.warning("language %s not recognized" % value)

                    # FIXME: Its not clear why we shouldn't just
                    # revert to unknown. I think this is more likely a
                    # bug / unintended behavior in gcc. Not very
                    # important though.
                    inputType = Types.ObjectType

        # We claim things here so that options for which we silently allow
        # override only ever claim the used option.
        if hasCombine:
            self.claim(hasCombine)

        finalPhase = Phases.Phase.eOrderPostAssemble
        finalPhaseOpt = None

        # Determine what compilation mode we are in.
        if hasDashE or hasDashM or hasDashMM:
            finalPhase = Phases.Phase.eOrderPreprocess
            finalPhaseOpt = hasDashE
        elif hasSyntaxOnly:
            finalPhase = Phases.Phase.eOrderCompile
            finalPhaseOpt = hasSyntaxOnly
        elif hasDashS:
            finalPhase = Phases.Phase.eOrderCompile
            finalPhaseOpt = hasDashS
        elif hasDashC:
            finalPhase = Phases.Phase.eOrderAssemble
            finalPhaseOpt = hasDashC    

        if finalPhaseOpt:
            self.claim(finalPhaseOpt)

        # FIXME: Support -combine.
        if hasCombine:
            raise NotImplementedError,"-combine is not yet supported"
        
        # Reject -Z* at the top level for now.
        arg = args.getLastArg(self.parser.ZOption)
        if arg:
            raise Arguments.InvalidArgumentsError("%s: unsupported use of internal gcc option" % ' '.join(args.render(arg)))

        if (not inputs and 
            not args.getLastArg(self.parser.hashHashHashOption)):
            raise Arguments.InvalidArgumentsError("no input files")

        actions = []
        linkerInputs = []
        # FIXME: This is gross.
        linkPhase = Phases.LinkPhase()
        for klass,input in inputs:
            # Figure out what step to start at.

            # FIXME: This should be part of the input class probably?
            # Altough it doesn't quite fit there either, things like
            # asm-with-preprocess don't easily fit into a linear scheme.

            # FIXME: I think we are going to end up wanting to just build
            # a simple FSA which we run the inputs down.
            sequence = []
            if klass.preprocess:
                sequence.append(Phases.PreprocessPhase())
            if klass == Types.ObjectType:
                sequence.append(linkPhase)
            elif klass.onlyAssemble:
                sequence.extend([Phases.AssemblePhase(),
                                 linkPhase])
            elif klass.onlyPrecompile:
                sequence.append(Phases.PrecompilePhase())
            else:
                sequence.extend([Phases.CompilePhase(),
                                 Phases.AssemblePhase(),
                                 linkPhase])

            if sequence[0].order > finalPhase:
                assert finalPhaseOpt and finalPhaseOpt.opt
                # FIXME: Explain what type of input file is. Or just match
                # gcc warning.
                self.warning("%s: %s input file unused when %s is present" % (args.getValue(input),
                                                                              sequence[0].name,
                                                                              finalPhaseOpt.opt.name))
            else:
                # Build the pipeline for this file.

                current = Phases.InputAction(input, klass)
                for transition in sequence:
                    # If the current action produces no output, or we are
                    # past what the user requested, we are done.
                    if (current.type is Types.NothingType or
                        transition.order > finalPhase):
                        break
                    else:
                        if isinstance(transition, Phases.PreprocessPhase):
                            assert isinstance(klass.preprocess, Types.InputType)
                            current = Phases.JobAction(transition,
                                                       [current],
                                                       klass.preprocess)
                        elif isinstance(transition, Phases.PrecompilePhase):
                            current = Phases.JobAction(transition,
                                                       [current],
                                                       Types.PCHType)
                        elif isinstance(transition, Phases.CompilePhase):
                            if hasSyntaxOnly:
                                output = Types.NothingType
                            else:
                                output = Types.AsmTypeNoPP
                            current = Phases.JobAction(transition,
                                                       [current],
                                                       output)
                        elif isinstance(transition, Phases.AssemblePhase):
                            current = Phases.JobAction(transition,
                                                       [current],
                                                       Types.ObjectType)
                        elif transition is linkPhase:
                            linkerInputs.append(current)
                            current = None
                            break
                        else:
                            raise RuntimeError,'Unrecognized transition: %s.' % transition
                        pass

                if current is not None:
                    assert not isinstance(current, Phases.InputAction)
                    actions.append(current)

        if linkerInputs:
            actions.append(Phases.JobAction(linkPhase,
                                            linkerInputs, 
                                            Types.ImageType))

        return actions

    def buildPipeline(self, args):
        # FIXME: We need to handle canonicalization of the specified arch.

        archs = {}
        hasDashM = args.getLastArg(self.parser.MGroup)
        hasSaveTemps = (args.getLastArg(self.parser.saveTempsOption) or 
                        args.getLastArg(self.parser.saveTempsOption2))
        for arg in args:
            if arg.opt is self.parser.archOption:
                # FIXME: Canonicalize this.
                archName = args.getValue(arg)
                archs[archName] = arg
        
        archs = archs.values()
        if not archs:
            archs.append(args.makeSeparateArg(self.hostInfo.getArchName(args),
                                              self.parser.archOption))

        actions = self.buildNormalPipeline(args)

        # FIXME: Use custom exception for this.
        #
        # FIXME: We killed off some others but these aren't yet detected in
        # a functional manner. If we added information to jobs about which
        # "auxiliary" files they wrote then we could detect the conflict
        # these cause downstream.
        if len(archs) > 1:
            if hasDashM:
                raise Arguments.InvalidArgumentsError("Cannot use -M options with multiple arch flags.")
            elif hasSaveTemps:
                raise Arguments.InvalidArgumentsError("Cannot use -save-temps with multiple arch flags.")

        # Execute once per arch.
        finalActions = []
        for p in actions:
            #  Make sure we can lipo this kind of output. If not (and it
            #  is an actual output) then we disallow, since we can't
            #  create an output file with the right name without
            #  overwriting it. We could remove this oddity by just
            #  changing the output names to include the arch, which would
            #  also fix -save-temps. Compatibility wins for now.
            #
            # FIXME: Is this error substantially less useful than
            # gcc-dd's? The main problem is that "Cannot use compiler
            # output with multiple arch flags" won't make sense to most
            # developers.
            if (len(archs) > 1 and
                p.type not in (Types.NothingType,Types.ObjectType,Types.ImageType)):
                raise Arguments.InvalidArgumentsError('Cannot use %s output with multiple arch flags.' % p.type.name)

            inputs = []
            for arch in archs:
                inputs.append(Phases.BindArchAction(p, arch))

            # Lipo if necessary. We do it this way because we need to set
            # the arch flag so that -Xarch_ gets rewritten.
            if len(inputs) == 1 or p.type == Types.NothingType:
                finalActions.extend(inputs)
            else:
                finalActions.append(Phases.JobAction(Phases.LipoPhase(),
                                                     inputs, 
                                                     p.type))

        return finalActions

    def bindPhases(self, phases, args):
        jobs = Jobs.JobList()

        finalOutput = args.getLastArg(self.parser.oOption)
        hasSaveTemps = (args.getLastArg(self.parser.saveTempsOption) or
                        args.getLastArg(self.parser.saveTempsOption2))
        hasNoIntegratedCPP = args.getLastArg(self.parser.noIntegratedCPPOption)
        hasTraditionalCPP = args.getLastArg(self.parser.traditionalCPPOption)
        hasPipe = args.getLastArg(self.parser.pipeOption)

        # We claim things here so that options for which we silently allow
        # override only ever claim the used option.
        if hasPipe:
            self.claim(hasPipe)
            # FIXME: Hack, override -pipe till we support it.
            if hasSaveTemps:
                self.warning('-pipe ignored because -save-temps specified')
                hasPipe = None
        # Claim these here. Its not completely accurate but any warnings
        # about these being unused are likely to be noise anyway.
        if hasSaveTemps:
            self.claim(hasSaveTemps)

        if hasTraditionalCPP:
            self.claim(hasTraditionalCPP)
        elif hasNoIntegratedCPP:
            self.claim(hasNoIntegratedCPP)
        
        # FIXME: Move to... somewhere else.
        class InputInfo:
            def __init__(self, source, type, baseInput):
                self.source = source
                self.type = type
                self.baseInput = baseInput

            def __repr__(self):
                return '%s(%r, %r, %r)' % (self.__class__.__name__,
                                           self.source, self.type, self.baseInput)
            
            def isOriginalInput(self):
                return self.source is self.baseInput

        def createJobs(tc, phase,
                       canAcceptPipe=False, atTopLevel=False, arch=None,
                       tcArgs=None, linkingOutput=None):
            if isinstance(phase, Phases.InputAction):
                return InputInfo(phase.filename, phase.type, phase.filename)
            elif isinstance(phase, Phases.BindArchAction):
                archName = args.getValue(phase.arch)
                tc = self.hostInfo.getToolChainForArch(archName)
                return createJobs(tc, phase.inputs[0],
                                  canAcceptPipe, atTopLevel, phase.arch,
                                  None, linkingOutput)

            if tcArgs is None:
                tcArgs = tc.translateArgs(args, arch)

            assert isinstance(phase, Phases.JobAction)
            tool = tc.selectTool(phase)

            # See if we should use an integrated CPP. We only use an
            # integrated cpp when we have exactly one input, since this is
            # the only use case we care about.
            useIntegratedCPP = False
            inputList = phase.inputs
            if (not hasNoIntegratedCPP and 
                not hasTraditionalCPP and
                not hasSaveTemps and
                tool.hasIntegratedCPP()):
                if (len(phase.inputs) == 1 and 
                    isinstance(phase.inputs[0], Phases.JobAction) and
                    isinstance(phase.inputs[0].phase, Phases.PreprocessPhase)):
                    useIntegratedCPP = True
                    inputList = phase.inputs[0].inputs

            # Only try to use pipes when exactly one input.
            canAcceptPipe = len(inputList) == 1 and tool.acceptsPipedInput()
            inputs = [createJobs(tc, p, canAcceptPipe, False, 
                                 arch, tcArgs, linkingOutput)
                      for p in inputList]

            # Determine if we should output to a pipe.
            canOutputToPipe = canAcceptPipe and tool.canPipeOutput()
            outputToPipe = False
            if canOutputToPipe:
                # Some things default to writing to a pipe if the final
                # phase and there was no user override.  
                # 
                # FIXME: What is the best way to handle this?
                if atTopLevel:
                    if (isinstance(phase.phase, Phases.PreprocessPhase) and 
                        not finalOutput):
                        outputToPipe = True
                elif hasPipe:
                    outputToPipe = True

            # Figure out where to put the job (pipes).
            jobList = jobs
            if canAcceptPipe and isinstance(inputs[0].source, Jobs.PipedJob):
                jobList = inputs[0].source
                
            baseInput = inputs[0].baseInput
            output = self.getOutputName(phase, outputToPipe, jobs, jobList, baseInput, 
                                        args, atTopLevel, hasSaveTemps, finalOutput)
            tool.constructJob(phase, arch, jobList, inputs, output, phase.type,
                              tcArgs, linkingOutput)

            return InputInfo(output, phase.type, baseInput)

        # It is an error to provide a -o option if we are making multiple
        # output files.
        if finalOutput and len([a for a in phases if a.type is not Types.NothingType]) > 1:
            raise Arguments.InvalidArgumentsError("cannot specify -o when generating multiple files")

        for phase in phases:
            # If we are linking an image for multiple archs then the
            # linker wants -arch_multiple and -final_output <final image
            # name>. Unfortunately this requires some gross contortions.
            #
            # FIXME: This is a hack; find a cleaner way to integrate this
            # into the process.        
            linkingOutput = None
            if (isinstance(phase, Phases.JobAction) and
                isinstance(phase.phase, Phases.LipoPhase)):
                finalOutput = args.getLastArg(self.parser.oOption)
                if finalOutput:
                    linkingOutput = finalOutput
                else:
                    linkingOutput = args.makeSeparateArg('a.out',
                                                         self.parser.oOption)

            createJobs(self.toolChain, phase, 
                       canAcceptPipe=True, atTopLevel=True,
                       linkingOutput=linkingOutput)

        return jobs

    def getOutputName(self, phase, outputToPipe, jobs, jobList, baseInput, 
                      args, atTopLevel, hasSaveTemps, finalOutput):
        # Figure out where to put the output.
        if phase.type == Types.NothingType:
            output = None            
        elif outputToPipe:
            if isinstance(jobList, Jobs.PipedJob):
                output = jobList
            else:
                jobList = output = Jobs.PipedJob([])
                jobs.addJob(output)
        else:
            # Figure out what the derived output location would be.
            # 
            # FIXME: gcc has some special case in here so that it doesn't
            # create output files if they would conflict with an input.
            if phase.type is Types.ImageType:
                namedOutput = "a.out"
            else:
                inputName = args.getValue(baseInput)
                base,_ = os.path.splitext(inputName)
                assert phase.type.tempSuffix is not None
                namedOutput = base + '.' + phase.type.tempSuffix

            # Output to user requested destination?
            if atTopLevel and finalOutput:
                output = finalOutput
            # Contruct a named destination?
            elif atTopLevel or hasSaveTemps:
                # As an annoying special case, pch generation
                # doesn't strip the pathname.
                if phase.type is Types.PCHType:
                    outputName = namedOutput
                else:
                    outputName = os.path.basename(namedOutput)
                output = args.makeSeparateArg(outputName,
                                              self.parser.oOption)
            else:
                # Output to temp file...
                fd,filename = tempfile.mkstemp(suffix='.'+phase.type.tempSuffix)
                output = args.makeSeparateArg(filename,
                                              self.parser.oOption)
        return output