[Bug rtl-optimization/47918] New: [4.6 regression] noreturn discovery broke non local gotos on m68k

[Bug rtl-optimization/47918] New: [4.6 regression] noreturn discovery broke non local gotos on m68k

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

           Summary: [4.6 regression] noreturn discovery broke non local
                    gotos on m68k
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: mikpe@it.uu.se


gcc.dg/torture/stackalign/non-local-goto-4.c and several similar test cases
fail with current 4.6 on m68k-linux.  Bisection identified r160124 as the
cause:

Author: hubicka
Date: Tue Jun  1 21:55:49 2010
New Revision: 160124

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=160124
Log:
    * ipa-pure-const.c (local_pure_const): Do NORETURN discovery.

The essence of non-local-goto-4.c is a function x() with a local self-recursive
function y() and a non-local goto from y() to x():

x(a)
{
  __label__ xlab;
  void y(a)
    {
      if (a==0)
        goto xlab;
      y (a-1);
    }
  y (a);
 xlab:;
  return a;
}

With r160123, gcc -O3 -fomit-frame-pointer -S generates this for x() and y():

        .text
        .align  2
        .type   y.1201, @function
y.1201:
        link.w %fp,#0
        move.l #.L2,%a1
        move.l (%a0),%fp
        move.l 4(%a0),%sp
        jmp (%a1)
        .size   y.1201, .-y.1201
        .align  2
        .globl  x
        .type   x, @function
x:
        lea (-12,%sp),%sp
        fmovem #252,-(%sp)
        movem.l #16190,-(%sp)
        lea (128,%sp),%a0
        move.l %a0,116(%sp)
        move.l %sp,120(%sp)
        move.l 132(%sp),-(%sp)
        lea (120,%sp),%a0
        jsr y.1201
        addq.l #4,%sp
.L4:
        move.l 132(%sp),%d0
        movem.l (%sp)+,#31996
        fmovem (%sp)+,#63
        lea (12,%sp),%sp
        rts
.L2:
        move.l 132(%sp),%d0
        movem.l (%sp)+,#31996
        fmovem (%sp)+,#63
        lea (12,%sp),%sp
        rts
        .size   x, .-x

This works.  But r160124 changes the code to:

        .align  2
        .type   y.1201, @function
y.1201:
        link.w %fp,#0
        move.l #.L2,%a1
        move.l (%a0),%fp
        move.l 4(%a0),%sp
        jmp (%a1)
        .size   y.1201, .-y.1201
        .align  2
        .globl  x
        .type   x, @function
x:
        lea (-12,%sp),%sp
        fmovem #252,-(%sp)
        movem.l #16190,-(%sp)
        lea (128,%sp),%a0
        move.l %a0,116(%sp)
        move.l %sp,120(%sp)
        move.l 132(%sp),-(%sp)
        lea (120,%sp),%a0
        jsr y.1201
.L2:
.L4:
        move.l 136(%sp),%d0
        movem.l (%sp)+,#31996
        fmovem (%sp)+,#63
        lea (12,%sp),%sp
        rts
        .size   x, .-x

A diff shows that L2 and L4 have been merged, a stack increment before L4 has
been removed and the stack offset for loading %d0 in L4 has been adjusted for
that.  However, the path leading up to L2 is the same as before, but L2 is now
the same as L4 so uses an incorrect (off-by-4) stack offset when fetching %d2.

--- non-local-goto-4.s-r160123  2011-02-27 23:44:28.000000000 +0100
+++ non-local-goto-4.s-r160124  2011-02-27 23:36:27.000000000 +0100
@@ -23,15 +23,9 @@
        move.l 132(%sp),-(%sp)
        lea (120,%sp),%a0
        jsr y.1201
-       addq.l #4,%sp
-.L4:
-       move.l 132(%sp),%d0
-       movem.l (%sp)+,#31996
-       fmovem (%sp)+,#63
-       lea (12,%sp),%sp
-       rts
 .L2:
-       move.l 132(%sp),%d0
+.L4:
+       move.l 136(%sp),%d0
        movem.l (%sp)+,#31996
        fmovem (%sp)+,#63
        lea (12,%sp),%sp

[Bug rtl-optimization/47918] [4.6 regression] noreturn discovery broke non local gotos on m68k

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.6.0

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-02-28 10:56:33 UTC ---
This is probably related to PR47815.

Also y isn't really noreturn, is it?  Honza?  Shouldn't non-local gotos
also prevent noreturn?

[Bug rtl-optimization/47918] [4.6 regression] noreturn discovery broke non local gotos on m68k

[joseph at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2011-02-28 20:28:27 UTC ---
On Mon, 28 Feb 2011, rguenth at gcc dot gnu.org wrote:

> Also y isn't really noreturn, is it?  Honza?  Shouldn't non-local gotos
> also prevent noreturn?

noreturn means a function does not return to its caller in the ordinary 
way; it says nothing about other control flow from that function 
(non-local gotos, longjmp, throwing exceptions).

[Bug rtl-optimization/47918] [4.6 Regression] noreturn discovery broke non local gotos on m68k

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P4
                 CC|                            |jakub at gcc dot gnu.org
            Summary|[4.6 regression] noreturn   |[4.6 Regression] noreturn
                   |discovery broke non local   |discovery broke non local
                   |gotos on m68k               |gotos on m68k

[Bug rtl-optimization/47918] [4.6 Regression] noreturn discovery broke non local gotos on m68k

[hubicka at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

--- Comment #3 from Jan Hubicka <hubicka at gcc dot gnu.org> 2011-03-07 13:53:50 UTC ---
I believe that the nonlocal gotos should be represented correctly in function
marked noreturn. So i think noreturn function can do nonlocal goto...

I get following CFG:

x (int a)
{
  struct FRAME.x FRAME.0;

  # BLOCK 2 freq:10000
  # PRED: ENTRY [100.0%]  (fallthru,exec)
  y (a_1(D)); [static-chain: &FRAME.0]
  # SUCC: 3 [100.0%]  (ab,exec)

  # BLOCK 3 freq:10000
  # PRED: 2 [100.0%]  (ab,exec)
<L0>: [non-local]
  # SUCC: 4 [100.0%]  (fallthru,exec)

  # BLOCK 4 freq:10000
  # PRED: 3 [100.0%]  (fallthru,exec)
xlab:
  return a_1(D);
  # SUCC: EXIT [100.0%]

}

this seems all right (i.e. there is abnormal edge to BB 3 for non-local goto)
We need to work out what really goes wrong for m68.

Honza

[Bug rtl-optimization/47918] [4.6/4.7 Regression] noreturn discovery broke non local gotos on m68k

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.6.0                       |4.6.1

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-25 19:52:39 UTC ---
GCC 4.6.0 is being released, adjusting target milestone.

[Bug rtl-optimization/47918] [4.6/4.7 Regression] noreturn discovery broke non local gotos on m68k

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.6.1                       |4.6.2

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-06-27 12:32:51 UTC ---
GCC 4.6.1 is being released.

[Bug rtl-optimization/47918] [4.6/4.7 Regression] noreturn discovery broke non local gotos on m68k

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

--- Comment #6 from Mikael Pettersson <mikpe at it dot uu.se> 2011-07-08 09:42:26 UTC ---
I can trigger the bug on i386 too, if I tweak the i386 backend to push function
parameters rather than moving them to pre-allocated stack space, and to
disallow regparm promotion for calls to non-exported functions, via this patch:

--- gcc-4.6-r160123/gcc/config/i386/i386.h.~1~  2010-05-29 16:03:31.000000000
+0200
+++ gcc-4.6-r160123/gcc/config/i386/i386.h      2011-07-08 10:43:46.000000000
+0200
@@ -1513,13 +1513,21 @@ enum reg_class
    prologue and apilogue.  This is not possible without
    ACCUMULATE_OUTGOING_ARGS.  */

+#if 0
 #define ACCUMULATE_OUTGOING_ARGS \
   (TARGET_ACCUMULATE_OUTGOING_ARGS || ix86_cfun_abi () == MS_ABI)
+#else
+#define ACCUMULATE_OUTGOING_ARGS 0
+#endif

 /* If defined, a C expression whose value is nonzero when we want to use PUSH
    instructions to pass outgoing arguments.  */

+#if 0
 #define PUSH_ARGS (TARGET_PUSH_ARGS && !ACCUMULATE_OUTGOING_ARGS)
+#else
+#define PUSH_ARGS 1
+#endif

 /* We want the stack and args grow in opposite directions, even if
    PUSH_ARGS is 0.  */
@@ -1804,7 +1812,11 @@ typedef struct ix86_args {
 #define X86_64_REGPARM_MAX 6
 #define X86_64_MS_REGPARM_MAX 4

+#if 0
 #define X86_32_REGPARM_MAX 3
+#else
+#define X86_32_REGPARM_MAX 0
+#endif

 #define REGPARM_MAX                                                    \
   (TARGET_64BIT ? (TARGET_64BIT_MS_ABI ? X86_64_MS_REGPARM_MAX         \

With that in place gcc still bootstraps ok on i686-linux, but r160124 now
miscompiles non-local-goto-4.c just like on m68k (see the changed and now
incorrect stack offset in the first insn after L4):

--- non-local-goto-4.s-r160123  2011-07-08 10:58:40.000000000 +0200
+++ non-local-goto-4.s-r160124  2011-07-08 11:24:05.000000000 +0200
@@ -25,19 +25,17 @@
        movl    %esp, 8(%esp)
        pushl   36(%esp)
        call    y.1220
-       popl    %eax
+       .p2align 4,,7
+       .p2align 3
+.L2:
 .L4:
-       movl    36(%esp), %eax
+       movl    40(%esp), %eax
        movl    16(%esp), %ebx
        movl    20(%esp), %esi
        movl    24(%esp), %edi
        movl    28(%esp), %ebp
        addl    $32, %esp
        ret
-       .p2align 4,,7
-       .p2align 3
-.L2:
-       jmp     .L4
        .size   x, .-x
        .p2align 4,,15
 .globl main

When I look at dumps everything looks ok up to .188r.asmcons, but in .191r.ira
I see a new load from the stack with the wrong offset.

[Bug rtl-optimization/47918] [4.6/4.7 Regression] noreturn discovery broke non local gotos on m68k and i386

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

Mikael Pettersson <mikpe at it dot uu.se> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|m68k-linux                  |m68k-linux,
                   |                            |i686-pc-linux-gnu
      Known to work|                            |4.5.3
            Summary|[4.6/4.7 Regression]        |[4.6/4.7 Regression]
                   |noreturn discovery broke    |noreturn discovery broke
                   |non local gotos on m68k     |non local gotos on m68k and
                   |                            |i386
      Known to fail|                            |4.6.1

--- Comment #7 from Mikael Pettersson <mikpe at it dot uu.se> 2011-07-08 10:56:32 UTC ---
I don't even have to tweak the i386 backend to trigger the error on i386, just
make the nested function y() regparm(0)

--- non-local-goto-4.c.~1~      2011-07-07 20:04:29.000000000 +0200
+++ non-local-goto-4.c  2011-07-08 12:49:36.000000000 +0200
@@ -15,7 +15,7 @@ int
 x(a)
 {
   __label__ xlab;
-  void y(a)
+  void __attribute__((regparm(0))) y(a)
     {
       if (a==0)
        goto xlab;

and compile with options to force the use of PUSH for parameter passing:

> gcc -O3 -fomit-frame-pointer -fno-asynchronous-unwind-tables -mpush-args -mno-accumulate-outgoing-args non-local-goto-4.c
> ./a.out
Abort

[Bug rtl-optimization/47918] [4.6/4.7 Regression] noreturn discovery broke non local gotos on m68k and i386

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.07.08 11:21:08
                 CC|                            |ebotcazou at gcc dot
                   |                            |gnu.org
     Ever Confirmed|0                           |1

--- Comment #8 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-07-08 11:21:08 UTC ---
This looks like a missing stack adjustment.  do_pending_stack_adjust needs to
be called before any potential control flow change.  Maybe such a call is
missing?

[Bug rtl-optimization/47918] [4.6/4.7 Regression] noreturn discovery broke non local gotos on m68k and i386

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

--- Comment #9 from Mikael Pettersson <mikpe at it dot uu.se> 2011-10-23 15:46:06 UTC ---
Julian Brown's proposed patch fixes non-local-goto-4.c on both m68k and i386:
http://gcc.gnu.org/ml/gcc-patches/2011-10/msg01657.html

[Bug rtl-optimization/47918] [4.6/4.7 Regression] noreturn discovery broke non local gotos on m68k and i386

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.6.2                       |4.6.3

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-10-26 17:13:38 UTC ---
GCC 4.6.2 is being released.

[Bug rtl-optimization/47918] [4.6/4.7 Regression] noreturn discovery broke non local gotos on m68k and i386

[jules at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

--- Comment #11 from jules at gcc dot gnu.org 2011-10-28 10:48:36 UTC ---
Author: jules
Date: Fri Oct 28 10:48:32 2011
New Revision: 180611

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=180611
Log:
    PR rtl-optimization/47918

    * reload1.c (set_initial_label_offsets): Use initial offsets
    for labels on the nonlocal_goto_handler_labels chain.


Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/reload1.c

[Bug rtl-optimization/47918] [4.6/4.7 Regression] noreturn discovery broke non local gotos on m68k and i386

[jules at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

--- Comment #12 from jules at gcc dot gnu.org 2011-11-01 18:38:45 UTC ---
Author: jules
Date: Tue Nov  1 18:38:42 2011
New Revision: 180740

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=180740
Log:
    PR rtl-optimization/47918

    * reload1.c (set_initial_label_offsets): Use initial offsets
    for labels on the nonlocal_goto_handler_labels chain.


Modified:
    branches/gcc-4_6-branch/gcc/ChangeLog
    branches/gcc-4_6-branch/gcc/reload1.c

[Bug rtl-optimization/47918] [4.6/4.7 Regression] noreturn discovery broke non local gotos on m68k and i386

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47918

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #13 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-11-01 18:58:19 UTC ---
Presumably everywhere.