https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127700
Bug ID: 127700
Summary: 32-bit constant loaded twice
Product: gcc
Version: 16.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: kuratius at googlemail dot com
Target Milestone: ---
Created attachment 65741
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=65741&action=edit
Sample code for producing the unoptimized assembly with arm-none-eabi-gcc -Os
-mcpu=arm946e-s -marm -S expbug.c
https://godbolt.org/z/vaK4TGnMv
First, it shouldn't reload the constant, and second it probably shouldn't
choose to use 4 separate imm adds instead of an ldr+add pair. imms might make
sense if the value is 16 or 24 bit, or if the value wasn't already in a
register.
Casting the table into a volatile pointer before accessing it fixes this, but
it's probably not ideal.
I tried going back a few versions, and I think this issue has probably existed
for a decade or so, GCC 9 also has a similar problem.
You can try compiling the sample code attached here with
arm-none-eabi-gcc -Os -mcpu=arm946e-s -marm -S expbug.c to see the assembly
output.
-O2 and -O3 have the same issue.
