[Mspgcc-users] State of link-time optimization (lto) in mspgcc

[Matthew T. C. <mta...@pu...>]

Hi,

I have searched the web for using lto with mspgcc, and it appears that 
it is not yet officially supported. However, minus one minor bug it does 
appear to work. The bug is if main is included in the lto then main does 
not show up in the binary. The obvious workaround is to place a wrapper 
around main. I give an example of what I mean below. The example shows 
that inlining across object files works (specifically the externally 
defined get_value is inlined in sub_main). It was compiled with 
mspgcc-20120911.

Can anyone comment further on the state of lto support in mspgcc? Are 
there any show stoppers I am likely to encounter when trying to compile 
more complex code than this simple example?

Thanks,
Matt

Makefile
01 CC=/usr/mspgcc-4.7.0/bin/msp430-gcc
02 COMPILE_FLAGS+= -mmcu=msp430f1611 -O -Os -mmpy=none -Wall -Wshadow
03
04 main.firmware: main.o sub_main.o inlineable_functions.o
05         $(CC) $(COMPILE_FLAGS) -flto -o $@ $^
06 main.o: main.c
07         $(CC) $(COMPILE_FLAGS) -c $^
08 sub_main.o: sub_main.c
09         $(CC) $(COMPILE_FLAGS) -flto -c $^
10 inlineable_functions.o: inlineable_functions.c
11         $(CC) $(COMPILE_FLAGS) -flto -c $^

main.c
01 extern int sub_main(void);
02 int main(void) {
03         return sub_main();
04 }

sub_main.c
01 extern int get_value(int i);
02 int sub_main(void) {
03         *((unsigned int*)200) = get_value(0);
04         return 0;
05 }

inlineable_functions.c
01 int get_value(int i) {
02         return i + 10;
03 }

main.firmware:     file format elf32-msp430
Disassembly of section .text:
00004000 <__watchdog_support>:
     4000:    55 42 20 01     mov.b    &0x0120,r5
     4004:    35 d0 08 5a     bis    #23048,    r5    ;#0x5a08
     4008:    82 45 00 11     mov    r5,    &0x1100
0000400c <__init_stack>:
     400c:    31 40 00 39     mov    #14592,    r1    ;#0x3900
00004010 <__do_copy_data>:
     4010:    3f 40 00 00     mov    #0,    r15    ;#0x0000
     4014:    0f 93           tst    r15
     4016:    08 24           jz    $+18         ;abs 0x4028
     4018:    92 42 00 11     mov    &0x1100,&0x0120
     401c:    20 01
     401e:    2f 83           decd    r15
     4020:    9f 4f 58 40     mov 16472(r15),4352(r15);0x4058(r15), 
0x1100(r15)
     4024:    00 11
     4026:    f8 23           jnz    $-14         ;abs 0x4018
00004028 <__do_clear_bss>:
     4028:    3f 40 00 00     mov    #0,    r15    ;#0x0000
     402c:    0f 93           tst    r15
     402e:    07 24           jz    $+16         ;abs 0x403e
     4030:    92 42 00 11     mov    &0x1100,&0x0120
     4034:    20 01
     4036:    1f 83           dec    r15
     4038:    cf 43 00 11     mov.b    #0,    4352(r15);r3 As==00, 
0x1100(r15)
     403c:    f9 23           jnz    $-12         ;abs 0x4030
0000403e <main>:
     403e:    b0 12 4c 40     call    #0x404c
00004042 <__stop_progExec__>:
     4042:    32 d0 f0 00     bis    #240,    r2    ;#0x00f0
     4046:    fd 3f           jmp    $-4          ;abs 0x4042
00004048 <__ctors_end>:
     4048:    30 40 56 40     br    #0x4056
0000404c <sub_main>:
     404c:    b2 40 0a 00     mov    #10,    &0x00c8    ;#0x000a
     4050:    c8 00
     4052:    0f 43           clr    r15
     4054:    30 41           ret
00004056 <_unexpected_>:
     4056:    00 13           reti