[dev.garbage] cmd/gc, runtime: implement write barriers in terms of writebarrierptr
This CL implements the many multiword write barriers by calling
writebarrierptr, so that only writebarrierptr needs the actual barrier.
In lieu of an actual barrier, writebarrierptr checks that the value
being copied is not a small non-zero integer. This is enough to
shake out bugs where the barrier is being called when it should not
(for non-pointer values). It also found a few tests in sync/atomic
that were being too clever.
This CL adds a write barrier for the memory moved during the
builtin copy function, which I forgot when inserting barriers for Go 1.4.
This CL re-enables some write barriers that were disabled for Go 1.4.
Those were disabled because it is possible to change the generated
code so that they are unnecessary most of the time, but we have not
changed the generated code yet. For safety they must be enabled.
None of this is terribly efficient. We are aiming for correct first.
LGTM=rlh
R=rlh
CC=golang-codereviews
https://golang.org/cl/168770043
diff --git a/src/cmd/gc/typecheck.c b/src/cmd/gc/typecheck.c
index 714c662..f05d802 100644
--- a/src/cmd/gc/typecheck.c
+++ b/src/cmd/gc/typecheck.c
@@ -2891,7 +2891,8 @@
case OSLICE3:
case OSLICESTR:
// For x = x[0:y], x can be updated in place, without touching pointer.
- if(samesafeexpr(n->left, n->right->left) && (n->right->right->left == N || iszero(n->right->right->left)))
+ // TODO(rsc): Reenable once it is actually updated in place without touching the pointer.
+ if(0 && samesafeexpr(n->left, n->right->left) && (n->right->right->left == N || iszero(n->right->right->left)))
n->right->reslice = 1;
break;
@@ -2899,7 +2900,8 @@
// For x = append(x, ...), x can be updated in place when there is capacity,
// without touching the pointer; otherwise the emitted code to growslice
// can take care of updating the pointer, and only in that case.
- if(n->right->list != nil && samesafeexpr(n->left, n->right->list->n))
+ // TODO(rsc): Reenable once the emitted code does update the pointer.
+ if(0 && n->right->list != nil && samesafeexpr(n->left, n->right->list->n))
n->right->reslice = 1;
break;
}
