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cgo: refactor union support

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Instead of putting the magic in the AST, generate regular accessor
methods. This avoids a number of special cases in the compiler, and
avoids missing any of them.

The resulting union accesses are somewhat clunkier to use, but the
compiler implementation has far less coupling between the CGo
implementation and the IR generator.
This commit is contained in:
Ayke van Laethem
2019-11-07 15:34:07 +01:00
committed by Ron Evans
parent 76c9f13e13
commit 6108ee6859
8 changed files with 340 additions and 174 deletions
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compiler/sizes.go
+6 -29
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@@ -63,12 +63,6 @@ func (s *StdSizes) Alignof(T types.Type) int64 {
func (s *StdSizes) Offsetsof(fields []*types.Var) []int64 {
offsets := make([]int64, len(fields))
if len(fields) > 1 && fields[0].Name() == "C union" {
// This struct contains the magic "C union" field which indicates that
// this is actually a union from CGo.
// All fields in the union start at 0 so return that.
return offsets // all fields are still set to 0
}
var o int64
for i, f := range fields {
a := s.Alignof(f.Type())
@@ -143,29 +137,12 @@ func (s *StdSizes) Sizeof(T types.Type) int64 {
maxAlign = al
}
}
if fields[0].Name() == "C union" {
// Magic field that indicates this is a CGo union and not a struct.
// The size is the biggest element, aligned to the element with the
// biggest alignment. This is not necessarily the same, for example
// in the following union:
// union { int32_t l; int16_t s[3] }
maxSize := int64(0)
for _, field := range fields[1:] {
si := s.Sizeof(field.Type())
if si > maxSize {
maxSize = si
}
}
return align(maxSize, maxAlign)
} else {
// This is a regular struct.
// Pick the size that fits this struct and add some alignment. Some
// structs have some extra padding at the end which should also be
// taken care of:
// struct { int32 n; byte b }
offsets := s.Offsetsof(fields)
return align(offsets[n-1]+s.Sizeof(fields[n-1].Type()), maxAlign)
}
// Pick the size that fits this struct and add some alignment. Some
// structs have some extra padding at the end which should also be taken
// care of:
// struct { int32 n; byte b }
offsets := s.Offsetsof(fields)
return align(offsets[n-1]+s.Sizeof(fields[n-1].Type()), maxAlign)
case *types.Interface:
return s.PtrSize * 2
case *types.Pointer: