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

["ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

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

--- Comment #1 from UroÅ Bizjak <ubizjak at gmail dot com> ---
(In reply to Michael Cree from comment #0)
> Created attachment 31837 [details]
> 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.

Because TLS_LD is defined in a wrong way.

        ldah $29,0($26)         !gpdisp!9
        .set    macro
 # 44 "gcc-optim-test.c" 1
        lda $16, foo($gp) !tlsldm
 # 0 "" 2
        .set    nomacro
        lda $29,0($29)          !gpdisp!9
        ldq $27,__tls_get_addr($29)             !literal!10
        jsr $26,($27),__tls_get_addr            !lituse_jsr!10

Please note how !gpdisp!9 gets emitted after !tlsldm load. Moving "lda
$29,0($29)" (and corresponding bar related insn) in front of !tlsldm load fixes
the ICE.