[Bug c/59820] New: alpha: incorrect optimisation with -mcpu=ev4 and -O2

["mcree at orcon dot net.nz" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59820

            Bug ID: 59820
           Summary: alpha: incorrect optimisation with -mcpu=ev4 and -O2
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mcree at orcon dot net.nz
            Target: alpha

Created attachment 31837
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31837&action=edit
Test code exhibiting problem

Compiling the attached test (which is a cut down version of a test from
glibc test suite) on an Alpha with -mcpu=ev4 at optimisation -O2 leads
to a segmentation fault when the test is run.   Output is:

$ gcc -mcpu=ev4 -O2 -o gcc-optim-test gcc-optim-test.c 
$ ./gcc-optim-test 
set bar to 1 (LE)
Segmentation fault

Compiling at lower optimisation works correctly, e.g.:

$ gcc -mcpu=ev4 -O1 -o gcc-optim-test gcc-optim-test.c 
$ ./gcc-optim-test 
set bar to 1 (LE)
get sum of foo and bar (LD) = 1

Compiling for more advanced Alpha CPU works correctly, even at -O2, e.g.:

$ gcc -mcpu=ev5 -O2 -o gcc-optim-test gcc-optim-test.c 
$ ./gcc-optim-test 
set bar to 1 (LE)
get sum of foo and bar (LD) = 1

Bug is seen on all versions of gcc tested ranging from gcc-4.4 upto gcc-4.8
from Debian, and gcc git master at commit eb5d7331da45b675e (SVN trunk
206563).

Running the failing version under gdb:

$ gcc -g -mcpu=ev4 -O2 -o gcc-optim-test gcc-optim-test.c 
$ gdb ./gcc-optim-test 
(gdb) run
Starting program: /home/mjc/test/./gcc-optim-test 
set bar to 1 (LE)

Program received signal SIGSEGV, Segmentation fault.
0x000002000001545c in __tls_get_addr () from /lib/ld-linux.so.2
(gdb) bt full
#0  0x000002000001545c in __tls_get_addr () from /lib/ld-linux.so.2
No symbol table info available.
#1  0x00000001200005a4 in do_test () at gcc-optim-test.c:44
        __result = 0x20000031230
        result = 0
        ap = <optimized out>
        bp = <optimized out>
#2  main () at gcc-optim-test.c:63
No locals.

(gdb) disass
Dump of assembler code for function __tls_get_addr:
   0x0000020000015420 <+0>:    ldah    gp,2(t12)
   0x0000020000015424 <+4>:    lda    gp,27728(gp)
   0x0000020000015428 <+8>:    lda    sp,-32(sp)
   0x000002000001542c <+12>:    rduniq
   0x0000020000015430 <+16>:    clr    a1
   0x0000020000015434 <+20>:    ldq    t0,-28776(gp)
   0x0000020000015438 <+24>:    stq    s0,8(sp)
   0x000002000001543c <+28>:    mov    a0,s0
   0x0000020000015440 <+32>:    ldq    a0,0(v0)
   0x0000020000015444 <+36>:    stq    s1,16(sp)
   0x0000020000015448 <+40>:    mov    v0,s1
   0x000002000001544c <+44>:    stq    ra,0(sp)
   0x0000020000015450 <+48>:    ldq    t1,0(a0)
   0x0000020000015454 <+52>:    cmpeq    t1,t0,t0
   0x0000020000015458 <+56>:    beq    t0,0x20000015494 <__tls_get_addr+116>
=> 0x000002000001545c <+60>:    ldq    a2,0(s0)

(gdb) info registers
v0             0x20000030b10    2199023454992
t0             0x1    1
t1             0x1    1
t2             0x29    41
t3             0x20000025ff0    2199023411184
t4             0x72616220646e6120    8241976684328149280
t5             0x6f660029444c2820    8027103563073988640
t6             0x61206f6f6620666f    6998716345179203183
t7             0x6120000000000000    6998593820933750784
s0             0x1200185d8    4831938008
s1             0x20000030b10    2199023454992
s2             0x120138388    4833117064
s3             0x0    0
s4             0x120143d90    4833164688
s5             0x120145330    4833170224
fp             0x0    0
a0             0x20000031230    2199023456816
a1             0x0    0
a2             0x0    0
a3             0x200001c8798    2199025125272
a4             0xffffffffffffffff    -1
a5             0x0    0
t8             0x28    40
t9             0x200000b7280    2199024005760
t10            0x11    17
t11            0x400    1024
ra             0x1200005a4    4831839652
t12            0x20000015420    2199023342624
at             0x7c8ad2d8    2089472728
gp             0x2000003c070    0x2000003c070
sp             0x11f8cd5c0    0x11f8cd5c0
pc             0x2000001545c    0x2000001545c <__tls_get_addr+60>
(gdb) print (long)*0x1200185d8
Cannot access memory at address 0x1200185d8

So it would appear that the argument passed to __tls_get_addr() was not
a valid address.