https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111672
Bug ID: 111672
Summary: Inappropriate function splitting during
pass_split_functions
Product: gcc
Version: 12.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: hkzhang455 at gmail dot com
Target Milestone: ---
Created attachment 56034
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56034&action=edit
example C file that can trigger inappropriate function splitting
When the GCC compiler performs function splitting optimization, the shorter and
closer path is split into a new function, while the remaining more complex and
expensive code is retained, resulting in the complexity of the original
function being increased after the split, and the split new function only
performs simple operations (such as 'printf()').
You can compile the source code file I put in the attachment with the following
command, and look at the gimple corresponding to the generated fnsplit to find
the phenomenon I described.
gcc test.c -O3 -flto -fdump-tree-fnsplit -Wall -Wextra
Of course, this is only sample code, so the resulting executable does not
reflect the efficiency gap due to the problem of inline. But in more complex
code, efficiency decreases.
Hardware: 12th Gen Intel(R) Core(TM) i9-12900KF
System: Ubuntu 22.04
Output of `gcc -v`:
Using built-in specs.
COLLECT_GCC=xxx/install/bin/gcc
COLLECT_LTO_WRAPPER=xxx/install/libexec/gcc/x86_64-pc-linux-gnu/12.3.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=xxx/install --enable-threads=posix
--disable-checking --disable-multilib --disable-bootstrap
--enable-languages=c,c++,lto
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.3.0 (GCC)
