// 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
}
// Emit a particular function.
func emitFunc(fn *ssa.Function) {
/* TODO research if the ssautil.Switches() function can be incorporated to provide any run-time improvement to the code
// it would give a big adavantage, but only to a very small number of functions - so definately TODO
sw := ssautil.Switches(fn)
fmt.Printf("DEBUG Switches for : %s \n", fn)
for num,swi := range sw {
fmt.Printf("DEBUG Switches[%d]= %+v\n", num, swi)
}
*/
var subFnList []subFnInstrs // where the sub-functions are
canOptMap := make(map[string]bool) // TODO review use of this mechanism
//println("DEBUG processing function: ", fn.Name())
MakePosHash(fn.Pos()) // mark that we have entered a function
trackPhi := true
switch len(fn.Blocks) {
case 0: // NoOp - only output a function if it has a body... so ignore pure definitions (target language may generate an error, if truely undef)
//fmt.Printf("DEBUG function has no body, ignored: %v %v \n", fn.Name(), fn.String())
case 1: // Only one block, so no Phi tracking required
trackPhi = false
fallthrough
default:
if trackPhi {
// check that there actually are Phi instructions to track
trackPhi = false
phiSearch:
for b := range fn.Blocks {
for i := range fn.Blocks[b].Instrs {
_, trackPhi = fn.Blocks[b].Instrs[i].(*ssa.Phi)
if trackPhi {
break phiSearch
}
}
}
}
instrCount := 0
for b := range fn.Blocks {
instrCount += len(fn.Blocks[b].Instrs)
}
mustSplitCode := false
if instrCount > LanguageList[TargetLang].InstructionLimit {
//println("DEBUG mustSplitCode => large function length:", instrCount, " in ", fn.Name())
mustSplitCode = true
}
blks := fn.DomPreorder() // was fn.Blocks
for b := range blks { // go though the blocks looking for sub-functions
instrsEmitted := 0
inSubFn := false
for i := range blks[b].Instrs {
canPutInSubFn := true
in := blks[b].Instrs[i]
switch in.(type) {
case *ssa.Phi: // phi uses self-referential temp vars that must be pre-initialised
canPutInSubFn = false
case *ssa.Return:
canPutInSubFn = false
case *ssa.Call:
switch in.(*ssa.Call).Call.Value.(type) {
case *ssa.Builtin:
//NoOp
default:
canPutInSubFn = false
}
case *ssa.Select, *ssa.Send, *ssa.Defer, *ssa.RunDefers, *ssa.Panic:
canPutInSubFn = false
case *ssa.UnOp:
if in.(*ssa.UnOp).Op == token.ARROW {
canPutInSubFn = false
}
}
if canPutInSubFn {
if inSubFn {
if instrsEmitted > LanguageList[TargetLang].SubFnInstructionLimit {
subFnList[len(subFnList)-1].end = i
subFnList = append(subFnList, subFnInstrs{b, i, 0})
instrsEmitted = 0
}
} else {
subFnList = append(subFnList, subFnInstrs{b, i, 0})
inSubFn = true
}
} else {
if inSubFn {
subFnList[len(subFnList)-1].end = i
inSubFn = false
}
}
instrsEmitted++
}
if inSubFn {
subFnList[len(subFnList)-1].end = len(blks[b].Instrs)
}
}
for sf := range subFnList { // go though the sub-functions looking for optimisable temp vars
var instrMap = make(map[ssa.Instruction]bool)
for ii := subFnList[sf].start; ii < subFnList[sf].end; ii++ {
instrMap[blks[subFnList[sf].block].Instrs[ii]] = true
}
for i := subFnList[sf].start; i < subFnList[sf].end; i++ {
instrVal, hasVal := blks[subFnList[sf].block].Instrs[i].(ssa.Value)
if hasVal {
refs := *blks[subFnList[sf].block].Instrs[i].(ssa.Value).Referrers()
switch len(refs) {
case 0: // no other instruction uses the result of this one
default: //multiple usage of the register
canOpt := true
for r := range refs {
user := refs[r]
if user.Block() != blks[subFnList[sf].block] {
canOpt = false
break
}
_, inRange := instrMap[user]
if !inRange {
canOpt = false
break
}
}
if canOpt &&
!LanguageList[TargetLang].CanInline(blks[subFnList[sf].block].Instrs[i]) {
canOptMap[instrVal.Name()] = true
}
}
}
}
}
reconstruct := tgossa.Reconstruct(blks, grMap[fn] || mustSplitCode)
if reconstruct != nil {
//fmt.Printf("DEBUG reconstruct %s %#v\n",fn.String(),reconstruct)
}
emitFuncStart(fn, blks, trackPhi, canOptMap, mustSplitCode, reconstruct)
thisSubFn := 0
for b := range blks {
emitPhi := trackPhi
emitBlockStart(blks, b, emitPhi)
inSubFn := false
for i := 0; i < len(blks[b].Instrs); i++ {
if thisSubFn >= 0 && thisSubFn < len(subFnList) { // not at the end of the list
if b == subFnList[thisSubFn].block {
if i >= subFnList[thisSubFn].end && inSubFn {
inSubFn = false
thisSubFn++
if thisSubFn >= len(subFnList) {
thisSubFn = -1 // we have come to the end of the list
}
}
}
}
if thisSubFn >= 0 && thisSubFn < len(subFnList) { // not at the end of the list
if b == subFnList[thisSubFn].block {
if i == subFnList[thisSubFn].start {
inSubFn = true
l := TargetLang
if mustSplitCode {
fmt.Fprintln(&LanguageList[l].buffer, LanguageList[l].SubFnCall(thisSubFn))
} else {
emitSubFn(fn, blks, subFnList, thisSubFn, mustSplitCode, canOptMap)
}
}
}
}
if !inSubFn {
// optimize phi case statements
phiList := 0
phiLoop:
switch blks[b].Instrs[i+phiList].(type) {
case *ssa.Phi:
if len(*blks[b].Instrs[i+phiList].(*ssa.Phi).Referrers()) > 0 {
phiList++
if (i + phiList) < len(blks[b].Instrs) {
goto phiLoop
}
}
}
if phiList > 0 {
peephole(blks[b].Instrs[i : i+phiList])
i += phiList - 1
} else {
emitPhi = emitInstruction(blks[b].Instrs[i],
blks[b].Instrs[i].Operands(make([]*ssa.Value, 0)))
}
}
}
if thisSubFn >= 0 && thisSubFn < len(subFnList) { // not at the end of the list
if b == subFnList[thisSubFn].block {
if inSubFn {
thisSubFn++
if thisSubFn >= len(subFnList) {
thisSubFn = -1 // we have come to the end of the list
}
}
}
}
emitBlockEnd(blks, b, emitPhi && trackPhi)
}
emitRunEnd(fn)
if mustSplitCode {
for sf := range subFnList {
emitSubFn(fn, blks, subFnList, sf, mustSplitCode, canOptMap)
}
}
emitFuncEnd(fn)
}
}
func (u *unit) defineFunction(f *ssa.Function) {
// Only define functions from this package, or synthetic
// wrappers (which do not have a package).
if f.Pkg != nil && f.Pkg != u.pkg {
return
}
llfn := u.resolveFunctionGlobal(f)
linkage := u.getFunctionLinkage(f)
isMethod := f.Signature.Recv() != nil
// Methods cannot be referred to via a descriptor.
if !isMethod {
llfd := u.resolveFunctionDescriptorGlobal(f)
llfd.SetInitializer(llvm.ConstBitCast(llfn, llvm.PointerType(llvm.Int8Type(), 0)))
llfd.SetLinkage(linkage)
}
// We only need to emit a descriptor for functions without bodies.
if len(f.Blocks) == 0 {
return
}
ssaopt.LowerAllocsToStack(f)
if u.DumpSSA {
f.WriteTo(os.Stderr)
}
fr := newFrame(u, llfn)
defer fr.dispose()
fr.addCommonFunctionAttrs(fr.function)
fr.function.SetLinkage(linkage)
fr.logf("Define function: %s", f.String())
fti := u.llvmtypes.getSignatureInfo(f.Signature)
delete(u.undefinedFuncs, f)
fr.retInf = fti.retInf
// Push the compile unit and function onto the debug context.
if u.GenerateDebug {
u.debug.PushFunction(fr.function, f.Signature, f.Pos())
defer u.debug.PopFunction()
u.debug.SetLocation(fr.builder, f.Pos())
}
// If a function calls recover, we create a separate function to
// hold the real function, and this function calls __go_can_recover
// and bridges to it.
if callsRecover(f) {
fr = fr.bridgeRecoverFunc(fr.function, fti)
}
fr.blocks = make([]llvm.BasicBlock, len(f.Blocks))
fr.lastBlocks = make([]llvm.BasicBlock, len(f.Blocks))
for i, block := range f.Blocks {
fr.blocks[i] = llvm.AddBasicBlock(fr.function, fmt.Sprintf(".%d.%s", i, block.Comment))
}
fr.builder.SetInsertPointAtEnd(fr.blocks[0])
prologueBlock := llvm.InsertBasicBlock(fr.blocks[0], "prologue")
fr.builder.SetInsertPointAtEnd(prologueBlock)
// Map parameter positions to indices. We use this
// when processing locals to map back to parameters
// when generating debug metadata.
paramPos := make(map[token.Pos]int)
for i, param := range f.Params {
paramPos[param.Pos()] = i
llparam := fti.argInfos[i].decode(llvm.GlobalContext(), fr.builder, fr.builder)
if isMethod && i == 0 {
if _, ok := param.Type().Underlying().(*types.Pointer); !ok {
llparam = fr.builder.CreateBitCast(llparam, llvm.PointerType(fr.types.ToLLVM(param.Type()), 0), "")
llparam = fr.builder.CreateLoad(llparam, "")
}
}
fr.env[param] = newValue(llparam, param.Type())
}
// Load closure, extract free vars.
if len(f.FreeVars) > 0 {
for _, fv := range f.FreeVars {
fr.env[fv] = newValue(llvm.ConstNull(u.llvmtypes.ToLLVM(fv.Type())), fv.Type())
}
elemTypes := make([]llvm.Type, len(f.FreeVars)+1)
elemTypes[0] = llvm.PointerType(llvm.Int8Type(), 0) // function pointer
for i, fv := range f.FreeVars {
elemTypes[i+1] = u.llvmtypes.ToLLVM(fv.Type())
}
structType := llvm.StructType(elemTypes, false)
closure := fr.runtime.getClosure.call(fr)[0]
closure = fr.builder.CreateBitCast(closure, llvm.PointerType(structType, 0), "")
for i, fv := range f.FreeVars {
ptr := fr.builder.CreateStructGEP(closure, i+1, "")
ptr = fr.builder.CreateLoad(ptr, "")
fr.env[fv] = newValue(ptr, fv.Type())
}
}
// Allocate stack space for locals in the prologue block.
for _, local := range f.Locals {
typ := fr.llvmtypes.ToLLVM(deref(local.Type()))
alloca := fr.builder.CreateAlloca(typ, local.Comment)
fr.memsetZero(alloca, llvm.SizeOf(typ))
bcalloca := fr.builder.CreateBitCast(alloca, llvm.PointerType(llvm.Int8Type(), 0), "")
value := newValue(bcalloca, local.Type())
fr.env[local] = value
if fr.GenerateDebug {
paramIndex, ok := paramPos[local.Pos()]
if !ok {
paramIndex = -1
}
fr.debug.Declare(fr.builder, local, alloca, paramIndex)
}
}
// If this is the "init" function, enable init-specific optimizations.
if !isMethod && f.Name() == "init" {
fr.isInit = true
}
// If the function contains any defers, we must first create
// an unwind block. We can short-circuit the check for defers with
// f.Recover != nil.
if f.Recover != nil || hasDefer(f) {
fr.unwindBlock = llvm.AddBasicBlock(fr.function, "")
fr.frameptr = fr.builder.CreateAlloca(llvm.Int8Type(), "")
}
term := fr.builder.CreateBr(fr.blocks[0])
fr.allocaBuilder.SetInsertPointBefore(term)
for _, block := range f.DomPreorder() {
fr.translateBlock(block, fr.blocks[block.Index])
}
fr.fixupPhis()
if !fr.unwindBlock.IsNil() {
fr.setupUnwindBlock(f.Recover, f.Signature.Results())
}
// The init function needs to register the GC roots first. We do this
// after generating code for it because allocations may have caused
// additional GC roots to be created.
if fr.isInit {
fr.builder.SetInsertPointBefore(prologueBlock.FirstInstruction())
fr.registerGcRoots()
}
}