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compiler: avoid zero-sized alloca in channel operations

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This works around a bug in LLVM
(https://bugs.llvm.org/show_bug.cgi?id=49916) but seems like a good
change in general.
This commit is contained in:
Ayke van Laethem
2021-09-08 17:07:10 +02:00
committed by Ron Evans
parent 485a9284e7
commit 6315db21f7
5 changed files with 169 additions and 10 deletions
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compiler/channel.go
+28 -9
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@@ -32,8 +32,15 @@ func (b *builder) createChanSend(instr *ssa.Send) {
// store value-to-send
valueType := b.getLLVMType(instr.X.Type())
valueAlloca, valueAllocaCast, valueAllocaSize := b.createTemporaryAlloca(valueType, "chan.value")
b.CreateStore(chanValue, valueAlloca)
isZeroSize := b.targetData.TypeAllocSize(valueType) == 0
var valueAlloca, valueAllocaCast, valueAllocaSize llvm.Value
if isZeroSize {
valueAlloca = llvm.ConstNull(llvm.PointerType(valueType, 0))
valueAllocaCast = llvm.ConstNull(b.i8ptrType)
} else {
valueAlloca, valueAllocaCast, valueAllocaSize = b.createTemporaryAlloca(valueType, "chan.value")
b.CreateStore(chanValue, valueAlloca)
}
// Allocate blockedlist buffer.
channelBlockedList := b.mod.GetTypeByName("runtime.channelBlockedList")
@@ -46,7 +53,9 @@ func (b *builder) createChanSend(instr *ssa.Send) {
// This also works around a bug in CoroSplit, at least in LLVM 8:
// https://bugs.llvm.org/show_bug.cgi?id=41742
b.emitLifetimeEnd(channelBlockedListAllocaCast, channelBlockedListAllocaSize)
b.emitLifetimeEnd(valueAllocaCast, valueAllocaSize)
if !isZeroSize {
b.emitLifetimeEnd(valueAllocaCast, valueAllocaSize)
}
}
// createChanRecv emits a pseudo chan receive operation. It is lowered to the
@@ -56,7 +65,14 @@ func (b *builder) createChanRecv(unop *ssa.UnOp) llvm.Value {
ch := b.getValue(unop.X)
// Allocate memory to receive into.
valueAlloca, valueAllocaCast, valueAllocaSize := b.createTemporaryAlloca(valueType, "chan.value")
isZeroSize := b.targetData.TypeAllocSize(valueType) == 0
var valueAlloca, valueAllocaCast, valueAllocaSize llvm.Value
if isZeroSize {
valueAlloca = llvm.ConstNull(llvm.PointerType(valueType, 0))
valueAllocaCast = llvm.ConstNull(b.i8ptrType)
} else {
valueAlloca, valueAllocaCast, valueAllocaSize = b.createTemporaryAlloca(valueType, "chan.value")
}
// Allocate blockedlist buffer.
channelBlockedList := b.mod.GetTypeByName("runtime.channelBlockedList")
@@ -64,9 +80,14 @@ func (b *builder) createChanRecv(unop *ssa.UnOp) llvm.Value {
// Do the receive.
commaOk := b.createRuntimeCall("chanRecv", []llvm.Value{ch, valueAllocaCast, channelBlockedListAlloca}, "")
received := b.CreateLoad(valueAlloca, "chan.received")
var received llvm.Value
if isZeroSize {
received = llvm.ConstNull(valueType)
} else {
received = b.CreateLoad(valueAlloca, "chan.received")
b.emitLifetimeEnd(valueAllocaCast, valueAllocaSize)
}
b.emitLifetimeEnd(channelBlockedListAllocaCast, channelBlockedListAllocaSize)
b.emitLifetimeEnd(valueAllocaCast, valueAllocaSize)
if unop.CommaOk {
tuple := llvm.Undef(b.ctx.StructType([]llvm.Type{valueType, b.ctx.Int1Type()}, false))
@@ -116,7 +137,6 @@ func (b *builder) createSelect(expr *ssa.Select) llvm.Value {
// determine the receive buffer size and alignment.
recvbufSize := uint64(0)
recvbufAlign := 0
hasReceives := false
var selectStates []llvm.Value
chanSelectStateType := b.getLLVMRuntimeType("chanSelectState")
for _, state := range expr.States {
@@ -133,7 +153,6 @@ func (b *builder) createSelect(expr *ssa.Select) llvm.Value {
if align := b.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.
@@ -150,7 +169,7 @@ func (b *builder) createSelect(expr *ssa.Select) llvm.Value {
// Create a receive buffer, where the received value will be stored.
recvbuf := llvm.Undef(b.i8ptrType)
if hasReceives {
if recvbufSize != 0 {
allocaType := llvm.ArrayType(b.ctx.Int8Type(), int(recvbufSize))
recvbufAlloca, _, _ := b.createTemporaryAlloca(allocaType, "select.recvbuf.alloca")
recvbufAlloca.SetAlignment(recvbufAlign)