On 05/08/2018 09:14 AM, Jan Hubicka wrote:
Hi, with lto, incremental linking can be meaninfuly done in three ways: 1) read LTO file and produce non-LTO .o file this is current behaviour of gcc -r or ld -r with plugin 2) read LTO files and merge section for later LTO this is current behaviour of ld -r w/o plugin 3) read LTO files into the compiler, link them and produce incrementaly linked LTO object.3 makes most sense and I am maing it new default for gcc -r. For testing purposes and perhaps in order to have tool to turn LTO object into real object, we want to have 1) available as well. GCC currently have -flinker-output option that decides between modes that is decided by linker plugin and can be overwritten by user (I have forgot to document this). I am targeting for -flinker-output=rel to be incremental linking into LTO and adding -flinker-output=nolto-rel for 1). The main limitation of 2 and 3 is that you can not link LTO and non-LTO object files theger. For 2 HJ's binutils patchset has support and I think it can be extended to handle 3 as well. But with default binutils we want to warn users. This patch implements the warning (and prevents linker plugin to add redundat linker-ouptut options.
This patch seems to have caused a lot of LTO tests in the G++ testsuite to fail on bare-metal targets because of the new warning. Here's a list for arm-none-eabi:
FAIL: g++.dg/lto/20091002-1 cp_lto_20091002-1_0.o-cp_lto_20091002-1_0.o link, -fPIC -flto -Wno-return-type FAIL: g++.dg/lto/20091219 cp_lto_20091219_0.o-cp_lto_20091219_0.o link, -O3 -flto FAIL: g++.dg/lto/pr64043 cp_lto_pr64043_0.o-cp_lto_pr64043_0.o link, -flto -std=c++11 FAIL: g++.dg/lto/pr65193 cp_lto_pr65193_0.o-cp_lto_pr65193_0.o link, -fPIC -r -nostdlib -flto -O2 -g -Wno-return-type FAIL: g++.dg/lto/pr65276 cp_lto_pr65276_0.o-cp_lto_pr65276_1.o link, -flto -O0 -std=c++11 FAIL: g++.dg/lto/pr65302 cp_lto_pr65302_0.o-cp_lto_pr65302_1.o link, -flto -O2 -Wno-return-type FAIL: g++.dg/lto/pr65316 cp_lto_pr65316_0.o-cp_lto_pr65316_1.o link, -flto -std=c++11 -g2 -fno-lto-odr-type-merging -O2 -Wno-return-type FAIL: g++.dg/lto/pr65549 cp_lto_pr65549_0.o-cp_lto_pr65549_0.o link, -std=gnu++14 -flto -g -Wno-return-type FAIL: g++.dg/lto/pr65549 cp_lto_pr65549_0.o-cp_lto_pr65549_0.o link, -std=gnu++14 -flto -g -O2 -fno-inline -flto-partition=max -Wno-return-type FAIL: g++.dg/lto/pr66180 cp_lto_pr66180_0.o-cp_lto_pr66180_1.o link, -flto -std=c++14 -r -nostdlib FAIL: g++.dg/lto/pr66705 cp_lto_pr66705_0.o-cp_lto_pr66705_0.o link, -O2 -flto -flto-partition=max -fipa-pta FAIL: g++.dg/lto/pr68057 cp_lto_pr68057_0.o-cp_lto_pr68057_1.o link, -O0 -flto -flto-partition=none -fuse-linker-plugin FAIL: g++.dg/lto/pr68057 cp_lto_pr68057_0.o-cp_lto_pr68057_1.o link, -O2 -flto -flto-partition=none -fuse-linker-plugin -fno-fat-lto-objects FAIL: g++.dg/lto/pr68057 cp_lto_pr68057_0.o-cp_lto_pr68057_1.o link, -O0 -flto -fuse-linker-plugin -fno-fat-lto-objects FAIL: g++.dg/lto/pr68057 cp_lto_pr68057_0.o-cp_lto_pr68057_1.o link, -O2 -flto -fuse-linker-plugin FAIL: g++.dg/lto/pr69077 cp_lto_pr69077_0.o-cp_lto_pr69077_1.o link, -O3 -g -flto FAIL: g++.dg/lto/pr69133 cp_lto_pr69133_0.o-cp_lto_pr69133_1.o link, -flto -O2 FAIL: g++.dg/lto/pr69137 cp_lto_pr69137_0.o-cp_lto_pr69137_0.o link, -std=c++11 -g -flto FAIL: g++.dg/lto/pr79000 cp_lto_pr79000_0.o-cp_lto_pr79000_1.o link, -flto -g FAIL: g++.dg/lto/pr81940 cp_lto_pr81940_0.o-cp_lto_pr81940_0.o link, -O -flto FAIL: g++.dg/lto/pr85176 cp_lto_pr85176_0.o-cp_lto_pr85176_0.o link, -flto -g1
I got a similar list on the csky-elf port I'm preparing for submission, but I didn't see any of these FAILs for csky-linux-gnu. LTO is a mysterious black box to me, but maybe it has something to do with linking with static vs shared libraries? Or some linker script issue? I see part 8 of this patch series touched a whole bunch of other test cases, but not these.
-Sandra
