https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113741
Bug ID: 113741
Summary: missed / wrong optimization switch transformation to
same function call
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: b.buschinski at googlemail dot com
Target Milestone: ---
Created attachment 57308
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57308&action=edit
Attached code + asm from the compiler explorer link
Compiler Explorer Link: https://godbolt.org/z/KozK9M5YY
The code is reduced from a "hot" path with huge macros.
I actually improved the macros with adding the "else" in the code, but I
noticed it suddenly created even more instructions and got slower.
The GCC version has 52 ASM lines.
The clang version only 9 ASM lines.
Clang is doing a better job here.
As far as I understand the ASM code, GCC generates a switch statement, but
after the:
cmp edi, 5
ja .L11
it should not be needed at all anymore.
Additionally, GCC "reloads" the static values again
(for every .L*: label)
mov edi, 4
, which are already stored in "i" (C code).
Tested with GCC-13.2 and compiler explorer gcc "trunk".
On x86_64 Linux.
Please let me know if you need any additional details or if this report was
useful at all.
