[Bug target/49515] New: [4.7 Regression] gcc.dg/torture/tls/thr-init-2.c -O2 -fpic execution test failure

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49515

           Summary: [4.7 Regression] gcc.dg/torture/tls/thr-init-2.c  -O2
                    -fpic  execution test failure
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ubizjak@gmail.com
                CC: rth@gcc.gnu.org
            Target: alpha-linux-gnu


gcc.dg/torture/tls/thr-init-2.c  -O2  -fpic testcase fails on
alphaev68-pc-linux-gnu due to clobbering of $16 register.

The problematic function in the testcase compiles to (-O2 -fpic):

$test_code..ng:
    ldq $27,__tls_get_addr($29)        !literal!1
    lda $30,-16($30)
    stq $26,0($30)
    stq $9,8($30)
    .prologue 1
    mov $16,$9
    lda $16,fstat($29)        !tlsldm!1
    jsr $26,($27),__tls_get_addr        !lituse_tlsldm!1
    ldah $29,0($26)        !gpdisp!3
    ldah $1,fstat($0)        !dtprelhi
    ldq $26,0($30)
    lda $29,0($29)        !gpdisp!3
>>>	ldl $16,fstat($1)		!dtprello
>>>	addl $16,$9,$16
    ldq $9,8($30)
    addl $31,$16,$0
>>>	stl $16,fstat($1)		!dtprello
    lda $30,16($30)
    ret $31,($26),1

$ ./a.out
a=2 fstat=33554434
Aborted

The difference to working code from gcc-4.4.5 is:

@@ -26,17 +26,18 @@
     ldah $1,fstat($0)        !dtprelhi
     ldq $26,0($30)
     lda $29,0($29)        !gpdisp!3
-    ldl $0,fstat($1)        !dtprello
-    addl $0,$9,$0
+    ldl $16,fstat($1)        !dtprello
+    addl $16,$9,$16
     ldq $9,8($30)
-    stl $0,fstat($1)        !dtprello
+    addl $31,$16,$0
+    stl $16,fstat($1)        !dtprello
     lda $30,16($30)
     ret $31,($26),1

Please note that $0 is used instead (extra addl is just a move from $16 to $0).

Does !dtprello relocation need live $16 register? The relevant patterns in
alpha.md do not model that dependancy.