http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46176
Summary: profile feedback causes 20% linux kernel binary growth
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: andi-...@firstfloor.org
Recent gcc 4.6 snapshot on x86_64-linux.
I did an experimental patch to use profile feedback with the Linux kernel
With a very simple training run (covering only ~50% of the files partially)
Unfortunately recompiling with the feedback data leads to a 20% larger
binary. This is compiled using -O2.
Trained:
text data bss dec hex filename
13615040 1202668 1357680 16175388 f6d11c vmlinux
Untrained:
11136452 1200876 1357552 13694880 d0f7a0 vmlinux
Comparing the symbols with the largest growth I get:
add/remove: 674/2006 grow/shrink: 12172/4139 up/down: 3000900/-510189 (2490711)
function old new delta
r600_kms_blit_copy 2640 16394 +13754
static.do_con_write - 10681 +10681
r600_blit_copy 10605 21205 +10600
zlib_inflate 5459 15261 +9802
static.rv770_startup - 9541 +9541
e1000_setup_copper_link - 9510 +9510
e1000_diag_test 14064 22948 +8884
kmem_cache_create 1385 10227 +8842
I have not analyzed it in detail, but current suspicion is much
more aggressive inlining?
Note also that a lot of functions were using fallback profiling data
because the training load wasn't very good.
