[Bug target/29963] could speed up variable access with different object layout
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29963
--- Comment #3 from Oleg Endo olegendo at gcc dot gnu.org 2012-11-13 00:53:45
UTC ---
(In reply to comment #2)
But it is not uncommon to load the program into RAM before executing,
e.g. because the ROM it's stored in is too slow.
Newer SH2A devices with on-chip flash have some facilities to fix that ;)
In that case, you could indeed only do this optimization for constant
variables / arrays.
True. For example in such cases as:
const char* test (void)
{
return test;
}
.filesh_tmp.cpp
.text
.little
.section .rodata.str1.4,aMS,@progbits,1
.align 2
.LC0:
.string test
.text
.align 1
.global __Z4testv
.type __Z4testv, @function
__Z4testv:
mov.l .L2,r0
rts
nop
.L3:
.align 2
.L2:
.long.LC0
.size__Z4testv, .-__Z4testv
.identGCC: (GNU) 4.8.0 20121112 (experimental)
The string constant could be placed in .text instead of .rodata, even without
link time relaxation:
__Z4testv:
mova .L2,r0
rts
nop
.L3:
.align 2
.L2:
.string test
However, it might have negative effects on the overall constant pool usage. I
guess there should be a limit on the size (and the number of) elements that are
moved from .rodata to .text.
[Bug target/29963] could speed up variable access with different object layout
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29963 Oleg Endo olegendo at gcc dot gnu.org changed: What|Removed |Added CC||olegendo at gcc dot gnu.org --- Comment #1 from Oleg Endo olegendo at gcc dot gnu.org 2012-11-01 21:26:56 UTC --- I'm not sure how the proposed optimization could be done in a generic way. It would not work for code (i.e. text section) that resides in read-only memory, such as ROM or MMU read-only pages.
[Bug target/29963] could speed up variable access with different object layout
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29963 --- Comment #2 from Jorn Wolfgang Rennecke amylaar at gcc dot gnu.org 2012-11-01 21:42:12 UTC --- (In reply to comment #1) I'm not sure how the proposed optimization could be done in a generic way. It would not work for code (i.e. text section) that resides in read-only memory, such as ROM or MMU read-only pages. In that case, you could indeed only do this optimization for constant variables / arrays. But it is not uncommon to load the program into RAM before executing, e.g. because the ROM it's stored in is too slow. In this case, placing the program code in a writable segment is merely a matter of policy; the user would be expected have control if this optimization is enabled, taking into account if there are any overriding security concerns.
