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cmd/compile: []T where T is go:notinheap does not need write barriers

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Currently, assigning a []T where T is a go:notinheap type generates an
unnecessary write barrier for storing the slice pointer.

This fixes this by teaching HasHeapPointer that this type does not
have a heap pointer, and tweaking the lowering of slice assignments so
the pointer store retains the correct type rather than simply lowering
it to a *uint8 store.

Change-Id: I8bf7c66e64a7fefdd14f2bd0de8a5a3596340bab
Reviewed-on: https://go-review.googlesource.com/76027
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Austin Clements 2017-11-02 12:37:25 -04:00
parent 0838c0f2f9
commit 3a446d8652
3 changed files with 10 additions and 5 deletions
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5
src/cmd/compile/internal/gc/ssa.go
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@ -3736,8 +3736,9 @@ func (s *state) storeTypePtrs(t *types.Type, left, right *ssa.Value) {
ptr := s.newValue1(ssa.OpStringPtr, s.f.Config.Types.BytePtr, right)
s.vars[&memVar] = s.newValue3A(ssa.OpStore, types.TypeMem, s.f.Config.Types.BytePtr, left, ptr, s.mem())
case t.IsSlice():
ptr := s.newValue1(ssa.OpSlicePtr, s.f.Config.Types.BytePtr, right)
s.vars[&memVar] = s.newValue3A(ssa.OpStore, types.TypeMem, s.f.Config.Types.BytePtr, left, ptr, s.mem())
elType := types.NewPtr(t.Elem())
ptr := s.newValue1(ssa.OpSlicePtr, elType, right)
s.vars[&memVar] = s.newValue3A(ssa.OpStore, types.TypeMem, elType, left, ptr, s.mem())
case t.IsInterface():
// itab field is treated as a scalar.
idata := s.newValue1(ssa.OpIData, s.f.Config.Types.BytePtr, right)

2
src/cmd/compile/internal/types/type.go
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@ -1391,7 +1391,7 @@ func Haspointers1(t *Type, ignoreNotInHeap bool) bool {
}
return false
case TPTR32, TPTR64:
case TPTR32, TPTR64, TSLICE:
return !(ignoreNotInHeap && t.Elem().NotInHeap())
}

8
test/notinheap3.go
View File

@ -10,11 +10,13 @@ package p
type t1 struct {
x *nih
s []nih
y [1024]byte // Prevent write decomposition
}
type t2 struct {
x *ih
s []ih
y [1024]byte
}
@ -37,8 +39,10 @@ var (
func f() {
// Test direct writes
v1.x = nil // no barrier
v2.x = nil // ERROR "write barrier"
v1.x = nil // no barrier
v2.x = nil // ERROR "write barrier"
v1.s = []nih(nil) // no barrier
v2.s = []ih(nil) // ERROR "write barrier"
}
func g() {