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merged 2 commits into from
Jun 12, 2019
Merged

Implement non-blocking select statements #402

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8287404
compiler,runtime: store channel size in the channel itself
aykevl Jun 8, 2019
81826a2
compiler,runtime: implement non-blocking selects
aykevl Jun 8, 2019
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179 changes: 169 additions & 10 deletions compiler/channel.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@ package compiler
// or pseudo-operations that are lowered during goroutine lowering.

import (
"fmt"
"go/types"

"golang.org/x/tools/go/ssa"
Expand All @@ -12,11 +13,22 @@ import (

// emitMakeChan returns a new channel value for the given channel type.
func (c *Compiler) emitMakeChan(expr *ssa.MakeChan) (llvm.Value, error) {
chanType := c.getLLVMType(c.getRuntimeType("channel"))
size := c.targetData.TypeAllocSize(chanType)
chanType := c.getLLVMType(expr.Type())
size := c.targetData.TypeAllocSize(chanType.ElementType())
sizeValue := llvm.ConstInt(c.uintptrType, size, false)
ptr := c.createRuntimeCall("alloc", []llvm.Value{sizeValue}, "chan.alloc")
ptr = c.builder.CreateBitCast(ptr, llvm.PointerType(chanType, 0), "chan")
ptr = c.builder.CreateBitCast(ptr, chanType, "chan")
// Set the elementSize field
elementSizePtr := c.builder.CreateGEP(ptr, []llvm.Value{
llvm.ConstInt(c.ctx.Int32Type(), 0, false),
llvm.ConstInt(c.ctx.Int32Type(), 0, false),
}, "")
elementSize := c.targetData.TypeAllocSize(c.getLLVMType(expr.Type().(*types.Chan).Elem()))
if elementSize > 0xffff {
return ptr, c.makeError(expr.Pos(), fmt.Sprintf("element size is %d bytes, which is bigger than the maximum of %d bytes", elementSize, 0xffff))
}
elementSizeValue := llvm.ConstInt(c.ctx.Int16Type(), elementSize, false)
c.builder.CreateStore(elementSizeValue, elementSizePtr)
return ptr, nil
}

Expand All @@ -33,8 +45,7 @@ func (c *Compiler) emitChanSend(frame *Frame, instr *ssa.Send) {

// Do the send.
coroutine := c.createRuntimeCall("getCoroutine", nil, "")
valueSize := llvm.ConstInt(c.uintptrType, c.targetData.TypeAllocSize(chanValue.Type()), false)
c.createRuntimeCall("chanSend", []llvm.Value{coroutine, ch, valueAllocaCast, valueSize}, "")
c.createRuntimeCall("chanSend", []llvm.Value{coroutine, ch, valueAllocaCast}, "")

// End the lifetime of the alloca.
// This also works around a bug in CoroSplit, at least in LLVM 8:
Expand All @@ -53,8 +64,7 @@ func (c *Compiler) emitChanRecv(frame *Frame, unop *ssa.UnOp) llvm.Value {

// Do the receive.
coroutine := c.createRuntimeCall("getCoroutine", nil, "")
valueSize := llvm.ConstInt(c.uintptrType, c.targetData.TypeAllocSize(valueType), false)
c.createRuntimeCall("chanRecv", []llvm.Value{coroutine, ch, valueAllocaCast, valueSize}, "")
c.createRuntimeCall("chanRecv", []llvm.Value{coroutine, ch, valueAllocaCast}, "")
received := c.builder.CreateLoad(valueAlloca, "chan.received")
c.emitLifetimeEnd(valueAllocaCast, valueAllocaSize)

Expand All @@ -72,8 +82,157 @@ func (c *Compiler) emitChanRecv(frame *Frame, unop *ssa.UnOp) llvm.Value {

// emitChanClose closes the given channel.
func (c *Compiler) emitChanClose(frame *Frame, param ssa.Value) {
valueType := c.getLLVMType(param.Type().(*types.Chan).Elem())
valueSize := llvm.ConstInt(c.uintptrType, c.targetData.TypeAllocSize(valueType), false)
ch := c.getValue(frame, param)
c.createRuntimeCall("chanClose", []llvm.Value{ch, valueSize}, "")
c.createRuntimeCall("chanClose", []llvm.Value{ch}, "")
}

// emitSelect emits all IR necessary for a select statements. That's a
// non-trivial amount of code because select is very complex to implement.
func (c *Compiler) emitSelect(frame *Frame, expr *ssa.Select) llvm.Value {
if len(expr.States) == 0 {
// Shortcuts for some simple selects.
llvmType := c.getLLVMType(expr.Type())
if expr.Blocking {
// Blocks forever:
// select {}
c.createRuntimeCall("deadlockStub", nil, "")
return llvm.Undef(llvmType)
} else {
// No-op:
// select {
// default:
// }
retval := llvm.Undef(llvmType)
retval = c.builder.CreateInsertValue(retval, llvm.ConstInt(c.intType, 0xffffffffffffffff, true), 0, "")
return retval // {-1, false}
}
}

// This code create a (stack-allocated) slice containing all the select
// cases and then calls runtime.chanSelect to perform the actual select
// statement.
// Simple selects (blocking and with just one case) are already transformed
// into regular chan operations during SSA construction so we don't have to
// optimize such small selects.

// Go through all the cases. Create the selectStates slice and and
// determine the receive buffer size and alignment.
recvbufSize := uint64(0)
recvbufAlign := 0
hasReceives := false
var selectStates []llvm.Value
chanSelectStateType := c.getLLVMRuntimeType("chanSelectState")
for _, state := range expr.States {
ch := c.getValue(frame, state.Chan)
selectState := c.getZeroValue(chanSelectStateType)
selectState = c.builder.CreateInsertValue(selectState, ch, 0, "")
switch state.Dir {
case types.RecvOnly:
// Make sure the receive buffer is big enough and has the correct alignment.
llvmType := c.getLLVMType(state.Chan.Type().(*types.Chan).Elem())
if size := c.targetData.TypeAllocSize(llvmType); size > recvbufSize {
recvbufSize = size
}
if align := c.targetData.ABITypeAlignment(llvmType); align > recvbufAlign {
recvbufAlign = align
}
hasReceives = true
case types.SendOnly:
// Store this value in an alloca and put a pointer to this alloca
// in the send state.
sendValue := c.getValue(frame, state.Send)
alloca := c.createEntryBlockAlloca(sendValue.Type(), "select.send.value")
c.builder.CreateStore(sendValue, alloca)
ptr := c.builder.CreateBitCast(alloca, c.i8ptrType, "")
selectState = c.builder.CreateInsertValue(selectState, ptr, 1, "")
default:
panic("unreachable")
}
selectStates = append(selectStates, selectState)
}

// Create a receive buffer, where the received value will be stored.
recvbuf := llvm.Undef(c.i8ptrType)
if hasReceives {
allocaType := llvm.ArrayType(c.ctx.Int8Type(), int(recvbufSize))
recvbufAlloca := c.builder.CreateAlloca(allocaType, "select.recvbuf.alloca")
recvbufAlloca.SetAlignment(recvbufAlign)
recvbuf = c.builder.CreateGEP(recvbufAlloca, []llvm.Value{
llvm.ConstInt(c.ctx.Int32Type(), 0, false),
llvm.ConstInt(c.ctx.Int32Type(), 0, false),
}, "select.recvbuf")
}

// Create the states slice (allocated on the stack).
statesAllocaType := llvm.ArrayType(chanSelectStateType, len(selectStates))
statesAlloca := c.builder.CreateAlloca(statesAllocaType, "select.states.alloca")
for i, state := range selectStates {
// Set each slice element to the appropriate channel.
gep := c.builder.CreateGEP(statesAlloca, []llvm.Value{
llvm.ConstInt(c.ctx.Int32Type(), 0, false),
llvm.ConstInt(c.ctx.Int32Type(), uint64(i), false),
}, "")
c.builder.CreateStore(state, gep)
}
statesPtr := c.builder.CreateGEP(statesAlloca, []llvm.Value{
llvm.ConstInt(c.ctx.Int32Type(), 0, false),
llvm.ConstInt(c.ctx.Int32Type(), 0, false),
}, "select.states")
statesLen := llvm.ConstInt(c.uintptrType, uint64(len(selectStates)), false)

// Convert the 'blocking' flag on this select into a LLVM value.
blockingInt := uint64(0)
if expr.Blocking {
blockingInt = 1
}
blockingValue := llvm.ConstInt(c.ctx.Int1Type(), blockingInt, false)

// Do the select in the runtime.
results := c.createRuntimeCall("chanSelect", []llvm.Value{
recvbuf,
statesPtr, statesLen, statesLen, // []chanSelectState
blockingValue,
}, "")

// The result value does not include all the possible received values,
// because we can't load them in advance. Instead, the *ssa.Extract
// instruction will treat a *ssa.Select specially and load it there inline.
// Store the receive alloca in a sidetable until we hit this extract
// instruction.
if frame.selectRecvBuf == nil {
frame.selectRecvBuf = make(map[*ssa.Select]llvm.Value)
}
frame.selectRecvBuf[expr] = recvbuf

return results
}

// getChanSelectResult returns the special values from a *ssa.Extract expression
// when extracting a value from a select statement (*ssa.Select). Because
// *ssa.Select cannot load all values in advance, it does this later in the
// *ssa.Extract expression.
func (c *Compiler) getChanSelectResult(frame *Frame, expr *ssa.Extract) llvm.Value {
if expr.Index == 0 {
// index
value := c.getValue(frame, expr.Tuple)
index := c.builder.CreateExtractValue(value, expr.Index, "")
if index.Type().IntTypeWidth() < c.intType.IntTypeWidth() {
index = c.builder.CreateSExt(index, c.intType, "")
}
return index
} else if expr.Index == 1 {
// comma-ok
value := c.getValue(frame, expr.Tuple)
return c.builder.CreateExtractValue(value, expr.Index, "")
} else {
// Select statements are (index, ok, ...) where ... is a number of
// received values, depending on how many receive statements there
// are. They are all combined into one alloca (because only one
// receive can proceed at a time) so we'll get that alloca, bitcast
// it to the correct type, and dereference it.
recvbuf := frame.selectRecvBuf[expr.Tuple.(*ssa.Select)]
typ := llvm.PointerType(c.getLLVMType(expr.Type()), 0)
ptr := c.builder.CreateBitCast(recvbuf, typ, "")
return c.builder.CreateLoad(ptr, "")
}
}
27 changes: 6 additions & 21 deletions compiler/compiler.go
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Original file line number Diff line number Diff line change
Expand Up @@ -84,6 +84,7 @@ type Frame struct {
deferFuncs map[*ir.Function]int
deferInvokeFuncs map[string]int
deferClosureFuncs map[*ir.Function]int
selectRecvBuf map[*ssa.Select]llvm.Value
}

type Phi struct {
Expand Down Expand Up @@ -1445,9 +1446,11 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
x := c.getValue(frame, expr.X)
return c.parseConvert(expr.X.Type(), expr.Type(), x, expr.Pos())
case *ssa.Extract:
if _, ok := expr.Tuple.(*ssa.Select); ok {
return c.getChanSelectResult(frame, expr), nil
}
value := c.getValue(frame, expr.Tuple)
result := c.builder.CreateExtractValue(value, expr.Index, "")
return result, nil
return c.builder.CreateExtractValue(value, expr.Index, ""), nil
case *ssa.Field:
value := c.getValue(frame, expr.X)
if s := expr.X.Type().Underlying().(*types.Struct); s.NumFields() > 2 && s.Field(0).Name() == "C union" {
Expand Down Expand Up @@ -1696,25 +1699,7 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
c.builder.CreateStore(c.getZeroValue(iteratorType), it)
return it, nil
case *ssa.Select:
if len(expr.States) == 0 {
// Shortcuts for some simple selects.
llvmType := c.getLLVMType(expr.Type())
if expr.Blocking {
// Blocks forever:
// select {}
c.createRuntimeCall("deadlockStub", nil, "")
return llvm.Undef(llvmType), nil
} else {
// No-op:
// select {
// default:
// }
retval := llvm.Undef(llvmType)
retval = c.builder.CreateInsertValue(retval, llvm.ConstInt(c.intType, 0xffffffffffffffff, true), 0, "")
return retval, nil // {-1, false}
}
}
return llvm.Undef(c.getLLVMType(expr.Type())), c.makeError(expr.Pos(), "unimplemented: "+expr.String())
return c.emitSelect(frame, expr), nil
case *ssa.Slice:
if expr.Max != nil {
return llvm.Value{}, c.makeError(expr.Pos(), "todo: full slice expressions (with max): "+expr.Type().String())
Expand Down
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