Go patch committed: Record pointer var values to remove write barriers

[Ian Lance Taylor <iant at golang dot org>]

This Go patch records pointer var values to remove write barriers.  We
record when a local pointer variable is set to a value such that
indirecting through the pointer does not require a write barrier.  We
use that to eliminate write barriers when indirecting through that
local pointer variable.  We only keep this information per-block, so
it's not all that applicable.

This reduces the number of write barriers generated when compiling the
runtime package from 553 to 524.

The point of this is to eliminate a bad write barrier in the bytes
function in runtime/print.go.  Mark that function nowritebarrier so
that the problem does not recur.

Bootstrapped and ran Go testsuite on x86_64-pc-linux-gnu.  Committed
to mainline.

Ian

Attachment: patch.txt
Description: Text document