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package compiler
// This file provides IR transformations necessary for precise and portable
// garbage collectors.
import (
"go/token"
"golang.org/x/tools/go/ssa"
"tinygo.org/x/go-llvm"
)
// trackExpr inserts pointer tracking intrinsics for the GC if the expression is
// one of the expressions that need this.
func (b *builder) trackExpr(expr ssa.Value, value llvm.Value) {
// There are uses of this expression, Make sure the pointers
// are tracked during GC.
switch expr := expr.(type) {
case *ssa.Alloc, *ssa.MakeChan, *ssa.MakeMap:
// These values are always of pointer type in IR.
b.trackPointer(value)
case *ssa.Call, *ssa.Convert, *ssa.MakeClosure, *ssa.MakeInterface, *ssa.MakeSlice, *ssa.Next:
if !value.IsNil() {
b.trackValue(value)
}
case *ssa.Select:
if alloca, ok := b.selectRecvBuf[expr]; ok {
if alloca.IsAUndefValue().IsNil() {
b.trackPointer(alloca)
}
}
case *ssa.UnOp:
switch expr.Op {
case token.MUL:
// Pointer dereference.
b.trackValue(value)
case token.ARROW:
// Channel receive operator.
// It's not necessary to look at commaOk here, because in that
// case it's just an aggregate and trackValue will extract the
// pointer in there (if there is one).
b.trackValue(value)
}
case *ssa.BinOp:
switch expr.Op {
case token.ADD:
// String concatenation.
b.trackValue(value)
}
}
}
// trackValue locates pointers in a value (possibly an aggregate) and tracks the
// individual pointers
func (b *builder) trackValue(value llvm.Value) {
typ := value.Type()
switch typ.TypeKind() {
case llvm.PointerTypeKind:
b.trackPointer(value)
case llvm.StructTypeKind:
if !typeHasPointers(typ) {
return
}
numElements := typ.StructElementTypesCount()
for i := 0; i < numElements; i++ {
subValue := b.CreateExtractValue(value, i, "")
b.trackValue(subValue)
}
case llvm.ArrayTypeKind:
if !typeHasPointers(typ) {
return
}
numElements := typ.ArrayLength()
for i := 0; i < numElements; i++ {
subValue := b.CreateExtractValue(value, i, "")
b.trackValue(subValue)
}
}
}
// trackPointer creates a call to runtime.trackPointer, bitcasting the pointer
// first if needed. The input value must be of LLVM pointer type.
func (b *builder) trackPointer(value llvm.Value) {
b.createRuntimeCall("trackPointer", []llvm.Value{value, b.stackChainAlloca}, "")
}
// typeHasPointers returns whether this type is a pointer or contains pointers.
// If the type is an aggregate type, it will check whether there is a pointer
// inside.
func typeHasPointers(t llvm.Type) bool {
switch t.TypeKind() {
case llvm.PointerTypeKind:
return true
case llvm.StructTypeKind:
for _, subType := range t.StructElementTypes() {
if typeHasPointers(subType) {
return true
}
}
return false
case llvm.ArrayTypeKind:
if typeHasPointers(t.ElementType()) {
return true
}
return false
default:
return false
}
}
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