Add ${c,cxx}.deduplicate_export_libs() function

This function deduplicates interface library dependencies by removing
libraries that are also interface dependencies of the specified
libraries. This can result in significantly better build performance for
heavily interface-interdependent library families (for example, like Boost).

Typical usage:

import intf_libs = ...
import intf_libs += ...
...
import intf_libs += ...
intf_libs = $cxx.deduplicate_export_libs($intf_libs)

1 files changed, 7 insertions, 0 deletions

diff --git a/libbuild2/cc/link-rule.hxx b/libbuild2/cc/link-rule.hxx
index 3d801d6..0fc1790 100644
--- a/libbuild2/cc/link-rule.hxx
+++ b/libbuild2/cc/link-rule.hxx
@@ -214,6 +214,13 @@ namespace build2
       append_binless_modules (strings&, sha256*,
                               const scope&, action, const file&) const;
 
+      bool
+      deduplicate_export_libs (
+        const scope&,
+        const vector<name>&,
+        names&,
+        vector<reference_wrapper<const name>>* = nullptr) const;
+
       optional<path>
       find_system_library (const strings&) const;