https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83175
Bug ID: 83175
Summary: compiler optimizing the code corresponding to double
precision operations
Product: gcc
Version: 4.8.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: sbansal at ciena dot com
Target Milestone: ---
I am migrating my tool chain from 3.4.5 to 4.8.1.
Migration to 4.8.1 is working great till now but the only problem I am recently
encountering is about code getting optimized when some "double" operations are
done.
Source code :
=========================
553 unlockAddr1_f64 = (double*) thisVars(vol)->unlockAddr1;
554 unlockAddr2_f64 = (double*) thisVars(vol)->unlockAddr2;
555 cmd.word32[0] = ((command<<16) | command);
556 cmd.word32[1] = cmd.word32[0];
557 unlockAddr1_f64[0] = unlock1_cmd.fword64;
558 unlockAddr2_f64[0] = unlock2_cmd.fword64;
559 unlockAddr1_f64[0] = cmd.fword64;
Corresponding assembly with 3.4.5 (working good)
====================================================
/vobs/equinox_ne_bsp/kernel/sources/drivers/ffs/amd16x4mtdome.c:553
13adb0: 81 23 00 18 lwz r9,24(r3)
13adb4: 81 69 00 00 lwz r11,0(r9)
/vobs/equinox_ne_bsp/kernel/sources/drivers/ffs/amd16x4mtdome.c:554
13adb8: 81 49 00 04 lwz r10,4(r9)
/vobs/equinox_ne_bsp/kernel/sources/drivers/ffs/amd16x4mtdome.c:555
13adbc: 54 a0 80 1e rlwinm r0,r5,16,0,15
13adc0: 7c 00 2b 78 or r0,r0,r5
13adc4: 7c 07 03 78 mr r7,r0
/vobs/equinox_ne_bsp/kernel/sources/drivers/ffs/amd16x4mtdome.c:556
13adc8: 7c 08 03 78 mr r8,r0
/vobs/equinox_ne_bsp/kernel/sources/drivers/ffs/amd16x4mtdome.c:557
13adcc: 3d 20 00 67 lis r9,103
13add0: c8 09 7d 08 lfd f0,32008(r9)
13add4: d8 0b 00 00 stfd f0,0(r11)
/vobs/equinox_ne_bsp/kernel/sources/drivers/ffs/amd16x4mtdome.c:558
13add8: 3d 20 00 67 lis r9,103
13addc: c8 09 7d 10 lfd f0,32016(r9)
13ade0: d8 0a 00 00 stfd f0,0(r10)
/vobs/equinox_ne_bsp/kernel/sources/drivers/ffs/amd16x4mtdome.c:559
13ade4: 90 e1 00 08 stw r7,8(r1)
13ade8: 91 01 00 0c stw r8,12(r1)
13adec: c9 a1 00 08 lfd f13,8(r1)
13adf0: d9 ab 00 00 stfd f13,0(r11)
Corresponding assembly with 4.8.1 (not working well) :
================================================================
/vobs/equinox_ne_bsp/kernel/sources/drivers/ffs/amd16x4mtdome.c:554
138e04: 81 0a 00 04 lwz r8,4(r10)
/vobs/equinox_ne_bsp/kernel/sources/drivers/ffs/amd16x4mtdome.c:555
138e08: 54 aa 80 1e rlwinm r10,r5,16,0,15
138e0c: 7d 45 2b 78 or r5,r10,r5
/vobs/equinox_ne_bsp/kernel/sources/drivers/ffs/amd16x4mtdome.c:557
138e10: 3c e0 00 66 lis r7,102
/vobs/equinox_ne_bsp/kernel/sources/drivers/ffs/amd16x4mtdome.c:558
138e14: c8 07 01 c8 lfd f0,456(r7)
138e18: d8 08 00 00 stfd f0,0(r8)
/vobs/equinox_ne_bsp/kernel/sources/drivers/ffs/amd16x4mtdome.c:559
138e1c: 90 a9 00 00 stw r5,0(r9)
138e20: 90 a9 00 04 stw r5,4(r9)
The problem I see is that, no assembly instructions (lfd, stfd) are generated
corresponding to line 557 & 559. It seems compiler is doing some optimization.
Surprisingly, If I add some printf or debug code after line 558, these
instructions are getting generated and code works well.
I know 4.8.1 is no longer supported by GCC, but I would appreciate if you could
give some directions which I can look. Probably some flags etc which I can set.
let me know if you need more information.
Thanks.
Sumit
