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* [Bug debug/46724] New: Wrong debug info: Invalid variable location
@ 2010-11-30 14:33 krebbel at gcc dot gnu.org
  2010-11-30 14:37 ` [Bug debug/46724] " krebbel at gcc dot gnu.org
                   ` (13 more replies)
  0 siblings, 14 replies; 15+ messages in thread
From: krebbel at gcc dot gnu.org @ 2010-11-30 14:33 UTC (permalink / raw)
  To: gcc-bugs

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46724

           Summary: Wrong debug info: Invalid variable location
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: debug
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: krebbel@gcc.gnu.org


The guality/nrv-1.c testcase currently fails on s390x when compiled with -O2:

Breakpoint 1, f () at /build3/gcc-head/gcc/testsuite/gcc.dg/guality/nrv-1.c:20
20        a2.i[4] = 7;  /* { dg-final { gdb-test 20 "a2.i\[0\]" "42" } } */
Missing separate debuginfos, use: debuginfo-install glibc-2.12.1-2.s390x
(gdb) p a2.i[0]
$1 = -336596880

The memory location of 'a2' is given as being based on r1:
readelf --debug-dump=info
...
 <2><85>: Abbrev Number: 9 (DW_TAG_variable)
    <86>   DW_AT_name        : a2
    <89>   DW_AT_decl_file   : 1
    <8a>   DW_AT_decl_line   : 16
    <8b>   DW_AT_type        : <0x2d>
    <8f>   DW_AT_location    : 2 byte block: 71 0       (DW_OP_breg1: 0)
...

But in fact r1 is not used at all. Instead the location is in r2:

f:
.LFB0:
        .file 1 "/build3/gcc-head/gcc/testsuite/gcc.dg/guality/nrv-1.c"
        .loc 1 15 0
        .cfi_startproc
        .loc 1 17 0
        lhi     %r3,42
        st      %r3,0(%r2)    <-- a2.i[0] = 42;
        ...

a2 is returned by f. The address of the location where the return value should
reside is passed to f as implicit first parameter in r2.

Right before cprop_hardreg the code looks like this. r2 is copied into r1 and
r1 is used to reference a2. DECL_RTL (<retval>) is (mem/s:SI (reg/f:DI 1 %r1
[orig:45 D.1986 ] [45]).

nrv-1.c.201r.ce3:

(insn 2 8 47 2 (set (reg/f:DI 1 %r1 [orig:45 D.1986 ] [45])
        (reg:DI 2 %r2 [ D.1986 ]))
/build3/gcc-head/gcc/testsuite/gcc.dg/guality/nrv-1.c:15 62 {*movdi_64}
     (nil))

(insn 47 2 6 2 (set (reg:SI 3 %r3)
        (const_int 42 [0x2a]))
/build3/gcc-head/gcc/testsuite/gcc.dg/guality/nrv-1.c:17 66 {*movsi_zarch}
     (nil))

(insn 6 47 45 2 (set (mem/s:SI (reg/f:DI 1 %r1 [orig:45 D.1986 ] [45]) [2
<retval>.i+0 S4 A32])
        (reg:SI 3 %r3))
/build3/gcc-head/gcc/testsuite/gcc.dg/guality/nrv-1.c:17 66 {*movsi_zarch}
     (expr_list:REG_DEAD (reg:SI 3 %r3)
        (nil)))

Then r1 is propagated into insn 6 and insn 2 is removed in DCE while DECL_RTL
(<retval>) still references r1.

nrv-1.c.203r.cprop_hardreg:

(insn 2 8 47 2 (set (reg/f:DI 1 %r1 [orig:45 D.1986 ] [45])
        (reg:DI 2 %r2 [ D.1986 ]))
/build3/gcc-head/gcc/testsuite/gcc.dg/guality/nrv-1.c:15 62 {*movdi_64}
     (nil))

(insn 47 2 6 2 (set (reg:SI 3 %r3)
        (const_int 42 [0x2a]))
/build3/gcc-head/gcc/testsuite/gcc.dg/guality/nrv-1.c:17 66 {*movsi_zarch}
     (nil))

(insn 6 47 45 2 (set (mem/s:SI (reg/f:DI 2 %r2 [orig:45 D.1986 ] [45]) [2
<retval>.i+0 S4 A32])
        (reg:SI 3 %r3))
/build3/gcc-head/gcc/testsuite/gcc.dg/guality/nrv-1.c:17 66 {*movsi_zarch}
     (expr_list:REG_DEAD (reg:SI 3 %r3)
        (nil)))

When generating the debug info for a2 add_location_or_const_value_attribute
first tries to find an RTX for a2 directly by invoking rtl_for_decl_location p
on the VAR_DECL of a2 what returns NULL. It then invokes loc_list_from_tree
which uses the DECL_VALUE_EXPR of the a2 decl - this is <retval>.
rtl_for_decl_location then returns (mem/s:SI (reg/f:DI 1 %r1 [orig:45 D.1986 ]
[45]) for <retval>.


^ permalink raw reply	[flat|nested] 15+ messages in thread
end of thread, other threads:[~2011-01-19 22:00 UTC | newest]

Thread overview: 15+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2010-11-30 14:33 [Bug debug/46724] New: Wrong debug info: Invalid variable location krebbel at gcc dot gnu.org
2010-11-30 14:37 ` [Bug debug/46724] " krebbel at gcc dot gnu.org
2010-11-30 14:48 ` krebbel at gcc dot gnu.org
2010-12-02  9:51 ` [Bug debug/46724] [4.6 Regression] " krebbel at gcc dot gnu.org
2010-12-02 12:11 ` jakub at gcc dot gnu.org
2010-12-16  5:39 ` aoliva at gcc dot gnu.org
2010-12-17  6:14 ` aoliva at gcc dot gnu.org
2010-12-17  6:19 ` aoliva at gcc dot gnu.org
2010-12-17  8:55 ` jakub at gcc dot gnu.org
2010-12-17  9:44 ` jakub at gcc dot gnu.org
2010-12-18  8:02 ` aoliva at gcc dot gnu.org
2010-12-18  8:05 ` aoliva at gcc dot gnu.org
2010-12-22  3:49 ` aoliva at gcc dot gnu.org
2010-12-22  3:56 ` aoliva at gcc dot gnu.org
2011-01-19 22:08 ` aoliva at gcc dot gnu.org

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