compiler: omit a couple of write barriers

Programming / Compilers / GCC - ian [138bc75d-0d04-0410-961f-82ee72b054a4] - 13 September 2018 00:45 EDT

Omit a write barrier for s = s[0:] for a slice s. In this case the pointer is not changing and no write barrier is required.

Omit a write barrier for s = append(s, v) in the case where len(s) < cap(s) (and similarly when appending more
values). When the slice has enough capacity the pointer is not changing and no write barrier is required.

These changes are required to avoid write barriers in the method randomOrder.reset in the runtime package. That method is called from procresize, at a point where we do not want to allocate memory. Otherwise that method can use a write barrier, allocate memory, and break TestReadMemStats.

Reviewed-on: https://go-review.googlesource.com/134219

d3c55148e76 compiler: omit a couple of write barriers
gcc/go/gofrontend/MERGE | 2 +-
gcc/go/gofrontend/expressions.cc | 105 +++++++++++++++++++++++++++++++++++----
gcc/go/gofrontend/expressions.h | 11 +++-
gcc/go/gofrontend/statements.cc | 19 ++++++-
gcc/go/gofrontend/statements.h | 14 +++++-
gcc/go/gofrontend/wb.cc | 77 +++++++++++++++++++++++++---
6 files changed, 204 insertions(+), 24 deletions(-)

Upstream: gcc.gnu.org


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