// Switches examines the control-flow graph of fn and returns the
// set of inferred value and type switches.  A value switch tests an
// ssa.Value for equality against two or more compile-time constant
// values.  Switches involving link-time constants (addresses) are
// ignored.  A type switch type-asserts an ssa.Value against two or
// more types.
//
// The switches are returned in dominance order.
//
// The resulting switches do not necessarily correspond to uses of the
// 'switch' keyword in the source: for example, a single source-level
// switch statement with non-constant cases may result in zero, one or
// many Switches, one per plural sequence of constant cases.
// Switches may even be inferred from if/else- or goto-based control flow.
// (In general, the control flow constructs of the source program
// cannot be faithfully reproduced from the SSA representation.)
//
func Switches(fn *ssa.Function) []Switch {
	// Traverse the CFG in dominance order, so we don't
	// enter an if/else-chain in the middle.
	var switches []Switch
	seen := make(map[*ssa.BasicBlock]bool) // TODO(adonovan): opt: use ssa.blockSet
	for _, b := range fn.DomPreorder() {
		if x, k := isComparisonBlock(b); x != nil {
			// Block b starts a switch.
			sw := Switch{Start: b, X: x}
			valueSwitch(&sw, k, seen)
			if len(sw.ConstCases) > 1 {
				switches = append(switches, sw)
			}
		}

		if y, x, T := isTypeAssertBlock(b); y != nil {
			// Block b starts a type switch.
			sw := Switch{Start: b, X: x}
			typeSwitch(&sw, y, T, seen)
			if len(sw.TypeCases) > 1 {
				switches = append(switches, sw)
			}
		}
	}
	return switches
}

// makeFunction creates the shared function object (aka contour) for
// function fn and returns a 'func' value node that points to it.
//
func (a *analysis) makeFunction(fn *ssa.Function) nodeid {
	obj := a.makeFunctionObject(fn)
	a.funcObj[fn] = obj

	var comment string
	if a.log != nil {
		comment = fn.String()
	}
	id := a.addOneNode(fn.Type(), comment, nil)
	a.addressOf(id, obj)
	return id
}

// callSSA interprets a call to function fn with arguments args,
// and lexical environment env, returning its result.
// callpos is the position of the callsite.
//
func callSSA(i *interpreter, caller *frame, callpos token.Pos, fn *ssa.Function, args []value, env []value) value {
	if i.mode&EnableTracing != 0 {
		fset := fn.Prog.Fset
		// TODO(adonovan): fix: loc() lies for external functions.
		fmt.Fprintf(os.Stderr, "Entering %s%s.\n", fn, loc(fset, fn.Pos()))
		suffix := ""
		if caller != nil {
			suffix = ", resuming " + caller.fn.String() + loc(fset, callpos)
		}
		defer fmt.Fprintf(os.Stderr, "Leaving %s%s.\n", fn, suffix)
	}
	if fn.Enclosing == nil {
		name := fn.String()
		if ext := externals[name]; ext != nil {
			if i.mode&EnableTracing != 0 {
				fmt.Fprintln(os.Stderr, "\t(external)")
			}
			return ext(fn, args)
		}
		if fn.Blocks == nil {
			panic("no code for function: " + name)
		}
	}
	fr := &frame{
		i:      i,
		caller: caller, // currently unused; for unwinding.
		fn:     fn,
		env:    make(map[ssa.Value]value),
		block:  fn.Blocks[0],
		locals: make([]value, len(fn.Locals)),
	}
	for i, l := range fn.Locals {
		fr.locals[i] = zero(deref(l.Type()))
		fr.env[l] = &fr.locals[i]
	}
	for i, p := range fn.Params {
		fr.env[p] = args[i]
	}
	for i, fv := range fn.FreeVars {
		fr.env[fv] = env[i]
	}
	for fr.block != nil {
		runFrame(fr)
	}
	// Destroy the locals to avoid accidental use after return.
	for i := range fn.Locals {
		fr.locals[i] = bad{}
	}
	return fr.result
}

// findIntrinsic returns the constraint generation function for an
// intrinsic function fn, or nil if the function should be handled normally.
//
func (a *analysis) findIntrinsic(fn *ssa.Function) intrinsic {
	// Consult the *Function-keyed cache.
	// A cached nil indicates a normal non-intrinsic function.
	impl, ok := a.intrinsics[fn]
	if !ok {
		impl = intrinsicsByName[fn.String()] // may be nil

		if fn.Pkg != nil && a.reflectValueObj != nil && a.reflectValueObj.Pkg() == fn.Pkg.Object {
			if !a.config.Reflection {
				impl = ext۰NoEffect // reflection disabled
			} else if impl == nil {
				// Ensure all "reflect" code is treated intrinsically.
				impl = ext۰NotYetImplemented
			}
		}

		a.intrinsics[fn] = impl
	}
	return impl
}

func (u *unit) resolveFunction(f *ssa.Function) *LLVMValue {
	if v, ok := u.globals[f]; ok {
		return v
	}
	name := f.String()
	// It's possible that the function already exists in the module;
	// for example, if it's a runtime intrinsic that the compiler
	// has already referenced.
	llvmFunction := u.module.Module.NamedFunction(name)
	if llvmFunction.IsNil() {
		llvmType := u.llvmtypes.ToLLVM(f.Signature)
		llvmType = llvmType.StructElementTypes()[0].ElementType()
		if len(f.FreeVars) > 0 {
			// Add an implicit first argument.
			returnType := llvmType.ReturnType()
			paramTypes := llvmType.ParamTypes()
			vararg := llvmType.IsFunctionVarArg()
			blockElementTypes := make([]llvm.Type, len(f.FreeVars))
			for i, fv := range f.FreeVars {
				blockElementTypes[i] = u.llvmtypes.ToLLVM(fv.Type())
			}
			blockType := llvm.StructType(blockElementTypes, false)
			blockPtrType := llvm.PointerType(blockType, 0)
			paramTypes = append([]llvm.Type{blockPtrType}, paramTypes...)
			llvmType = llvm.FunctionType(returnType, paramTypes, vararg)
		}
		llvmFunction = llvm.AddFunction(u.module.Module, name, llvmType)
		if f.Enclosing != nil {
			llvmFunction.SetLinkage(llvm.PrivateLinkage)
		}
		u.undefinedFuncs[f] = true
	}
	v := u.NewValue(llvmFunction, f.Signature)
	u.globals[f] = v
	return v
}

func (u *unit) defineFunction(f *ssa.Function) {
	// Nothing to do for functions without bodies.
	if len(f.Blocks) == 0 {
		return
	}

	// Only define functions from this package.
	if f.Pkg == nil {
		if r := f.Signature.Recv(); r != nil && r.Pkg() != nil && r.Pkg() != u.pkg.Object {
			return
		}
	} else if f.Pkg != u.pkg {
		return
	}

	fr := frame{
		unit:   u,
		blocks: make([]llvm.BasicBlock, len(f.Blocks)),
		env:    make(map[ssa.Value]*LLVMValue),
	}

	fr.logf("Define function: %s", f.String())
	llvmFunction := fr.resolveFunction(f).LLVMValue()
	delete(u.undefinedFuncs, f)

	// Functions that call recover must not be inlined, or we
	// can't tell whether the recover call is valid at runtime.
	if f.Recover != nil {
		llvmFunction.AddFunctionAttr(llvm.NoInlineAttribute)
	}

	for i, block := range f.Blocks {
		fr.blocks[i] = llvm.AddBasicBlock(llvmFunction, fmt.Sprintf(".%d.%s", i, block.Comment))
	}
	fr.builder.SetInsertPointAtEnd(fr.blocks[0])

	var paramOffset int
	if len(f.FreeVars) > 0 {
		// Extract captures from the first implicit parameter.
		arg0 := llvmFunction.Param(0)
		for i, fv := range f.FreeVars {
			addressPtr := fr.builder.CreateStructGEP(arg0, i, "")
			address := fr.builder.CreateLoad(addressPtr, "")
			fr.env[fv] = fr.NewValue(address, fv.Type())
		}
		paramOffset++
	}
	for i, param := range f.Params {
		fr.env[param] = fr.NewValue(llvmFunction.Param(i+paramOffset), param.Type())
	}

	// Allocate stack space for locals in the prologue block.
	prologueBlock := llvm.InsertBasicBlock(fr.blocks[0], "prologue")
	fr.builder.SetInsertPointAtEnd(prologueBlock)
	for _, local := range f.Locals {
		typ := fr.llvmtypes.ToLLVM(deref(local.Type()))
		alloca := fr.builder.CreateAlloca(typ, local.Comment)
		u.memsetZero(alloca, llvm.SizeOf(typ))
		value := fr.NewValue(alloca, local.Type())
		fr.env[local] = value
	}

	// Move any allocs relating to named results from the entry block
	// to the prologue block, so they dominate the rundefers and recover
	// blocks.
	//
	// TODO(axw) ask adonovan for a cleaner way of doing this, e.g.
	// have ssa generate an entry block that defines Allocs and related
	// stores, and then a separate block for function body instructions.
	if f.Synthetic == "" {
		if results := f.Signature.Results(); results != nil {
			for i := 0; i < results.Len(); i++ {
				result := results.At(i)
				if result.Name() == "" {
					break
				}
				for i, instr := range f.Blocks[0].Instrs {
					if instr, ok := instr.(*ssa.Alloc); ok && instr.Heap && instr.Pos() == result.Pos() {
						fr.instruction(instr)
						instrs := f.Blocks[0].Instrs
						instrs = append(instrs[:i], instrs[i+1:]...)
						f.Blocks[0].Instrs = instrs
						break
					}
				}
			}
		}
	}

	// If the function contains any defers, we must first call
	// setjmp so we can call rundefers in response to a panic.
	// We can short-circuit the check for defers with
	// f.Recover != nil.
	if f.Recover != nil || hasDefer(f) {
		rdblock := llvm.AddBasicBlock(llvmFunction, "rundefers")
		defers := fr.builder.CreateAlloca(fr.runtime.defers.llvm, "")
		fr.builder.CreateCall(fr.runtime.initdefers.LLVMValue(), []llvm.Value{defers}, "")
		jb := fr.builder.CreateStructGEP(defers, 0, "")
		jb = fr.builder.CreateBitCast(jb, llvm.PointerType(llvm.Int8Type(), 0), "")
		result := fr.builder.CreateCall(fr.runtime.setjmp.LLVMValue(), []llvm.Value{jb}, "")
//.........这里部分代码省略.........

// callSSA interprets a call to function fn with arguments args,
// and lexical environment env, returning its result.
// callpos is the position of the callsite.
//
func callSSA(i *interpreter, caller *frame, callpos token.Pos, fn *ssa.Function, args []value, env []value) value {
	if i.mode&EnableTracing != 0 {
		fset := fn.Prog.Files
		// TODO(adonovan): fix: loc() lies for external functions.
		fmt.Fprintf(os.Stderr, "Entering %s%s.\n", fn.FullName(), loc(fset, fn.Pos()))
		suffix := ""
		if caller != nil {
			suffix = ", resuming " + caller.fn.FullName() + loc(fset, callpos)
		}
		defer fmt.Fprintf(os.Stderr, "Leaving %s%s.\n", fn.FullName(), suffix)
	}
	if fn.Enclosing == nil {
		name := fn.FullName()
		if ext := externals[name]; ext != nil {
			if i.mode&EnableTracing != 0 {
				fmt.Fprintln(os.Stderr, "\t(external)")
			}
			return ext(fn, args)
		}
		if fn.Blocks == nil {
			panic("no code for function: " + name)
		}
	}
	fr := &frame{
		i:      i,
		caller: caller, // currently unused; for unwinding.
		fn:     fn,
		env:    make(map[ssa.Value]value),
		block:  fn.Blocks[0],
		locals: make([]value, len(fn.Locals)),
	}
	for i, l := range fn.Locals {
		fr.locals[i] = zero(l.Type().Deref())
		fr.env[l] = &fr.locals[i]
	}
	for i, p := range fn.Params {
		fr.env[p] = args[i]
	}
	for i, fv := range fn.FreeVars {
		fr.env[fv] = env[i]
	}
	var instr ssa.Instruction

	defer func() {
		if fr.status != stComplete {
			if fr.i.mode&DisableRecover != 0 {
				return // let interpreter crash
			}
			fr.status, fr.panic = stPanic, recover()
		}
		fr.rundefers()
		// Destroy the locals to avoid accidental use after return.
		for i := range fn.Locals {
			fr.locals[i] = bad{}
		}
		if fr.status == stPanic {
			panic(fr.panic) // panic stack is not entirely clean
		}
	}()

	for {
		if i.mode&EnableTracing != 0 {
			fmt.Fprintf(os.Stderr, ".%s:\n", fr.block)
		}
	block:
		for _, instr = range fr.block.Instrs {
			if i.mode&EnableTracing != 0 {
				if v, ok := instr.(ssa.Value); ok {
					fmt.Fprintln(os.Stderr, "\t", v.Name(), "=", instr)
				} else {
					fmt.Fprintln(os.Stderr, "\t", instr)
				}
			}
			switch visitInstr(fr, instr) {
			case kReturn:
				fr.status = stComplete
				return fr.result
			case kNext:
				// no-op
			case kJump:
				break block
			}
		}
	}
	panic("unreachable")
}