tree 509265cf4aa0e6e8c30c61392062587833c828f3
parent c20b79310e18808e6d8061b8872be18d0c92f7dd
author Cherry Zhang <cherryyz@google.com> 1537583341 -0400
committer Cherry Zhang <cherryyz@google.com> 1544112772 +0000

passes: add a statepoint insertion pass

This pass performs liveness analysis and attaches the liveness
information to statepoints, to support precise stack scan for
the Go GC. Statepoints are function calls. Currently a
non-moving GC is implemented.

This pass is based on LLVM's RewriteStatepointsForGC pass, with
the following modifications:

- We implement a non-moving GC, so gc.relocate is not necessary.
  Related code are removed.

- The original code only tracks live in-register values. For Go,
  the GC roots also include stack allocated objects. So the
  liveness analysis is extended with stack slot (alloca)
  liveness tracking.

- We encode the stack maps in the exception table. To do that,
  we rewrite all the statepoint calls to may-throw invoke, and
  attach the stack map to the landing pad as the type info. For
  each statepoint we attach a symbol go..stackmap.ID, and later
  the stack map generation code will fill in the content of the
  symbol with the actual stack map.

TODO: have some way to unit test

Change-Id: I166135eb9ac753686e6b47d9ae84f7a746fb933f
Reviewed-on: https://go-review.googlesource.com/c/137761
Reviewed-by: Than McIntosh <thanm@google.com>