The LTO branch is starting to get some semblance of stability, though is by no means in any kind of mergeable state. I have updated the wiki page to reflect the current status (Simon, Rafael, Doug, Cary, please make sure I haven't missed anything substantial):
http://gcc.gnu.org/wiki/LinkTimeOptimization Essentially, the biggest areas where we need help are: - Testing on other targets. We have only tested on x86 (32 and 64 bit) targets. I'm pretty sure other targets are either non-functional or show major breakage. We'd appreciate any daily tester that could include the branch and report bugs to bugzilla (feel free to assign to me). - Help with testsuite regressions. There are currently around 1,200 regressions vs mainline. Some may not even be too gruesome to fix. We are currently testing the code with a set of internal large applications, which is what has been driving our patches, some times fixes we do happen to fix testsuite programs, but not always. This is a list of major issues that need to be addressed. The wiki page contains full details: * Re-implement the GIMPLE streamer * -v -save-temps does not always show everything needed to reproduce a compilation stage when using -fwhopr * -fwhopr should not launch the LTRANS phase from lto1 * WPA should use the pass manager * Design and implement rules for handling mixed command line options. * Browsing/dumping tools for LTO files * Implement a GIMPLE type system * Read GIMPLE from a text file * Improve serialization * Make nested functions work properly * Fix debug information for LTO programs * Test on other platforms * Aliasing information needs to be propagated all the way through LTO Thanks. Diego.