[Bug c/53085] New: write to volatile struct member is missing on Cortex-M3

[Bug c/53085] New: write to volatile struct member is missing on Cortex-M3

[unixoid2003 at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53085

             Bug #: 53085
           Summary: write to volatile struct member is missing on
                    Cortex-M3
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: unixoid2003@mail.ru


Created attachment 27221
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27221
test code

[Bug c/53085] write to volatile struct member is missing on Cortex-M3

[unixoid2003 at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53085

--- Comment #1 from brag <unixoid2003 at mail dot ru> 2012-04-23 12:58:17 UTC ---
struct aa{
    volatile unsigned short a;
    unsigned short b;
    volatile unsigned short c;
    unsigned short d;
};

#define AAmem ((struct aa *) 256)

static inline unsigned int tx(unsigned int v){
    while(AAmem->a&1);
    AAmem->c=v;
    while(AAmem->a&2);
    v=AAmem->c;
    return v;
}

void f(){
    tx(0xff);
    tx(0xff);
}

Compiled by:
arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -O2 -fomit-frame-pointer
-ffreestanding -fno-common -Wall -Wextra -x c -c test.cpp
OR
arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -O2 -fomit-frame-pointer
-ffreestanding -fno-common -Wall -Wextra -x c++ -c test.cpp

The code generated is wrong. There should be two writes to AAmem->c bute there
is one write (strh    r3, [r2, #4])

arm-none-eabi-objdump -d test.o :
test.o:     file format elf32-littlearm


Disassembly of section .text:

00000000 <f>:
   0:    f44f 7180     mov.w    r1, #256    ; 0x100
   4:    880b          ldrh    r3, [r1, #0]
   6:    f44f 7280     mov.w    r2, #256    ; 0x100
   a:    07d8          lsls    r0, r3, #31
   c:    d4fa          bmi.n    4 <f+0x4>
   e:    23ff          movs    r3, #255    ; 0xff
  10:    8093          strh    r3, [r2, #4]
  12:    4611          mov    r1, r2
  14:    880b          ldrh    r3, [r1, #0]
  16:    f44f 7280     mov.w    r2, #256    ; 0x100
  1a:    f003 0302     and.w    r3, r3, #2
  1e:    b29b          uxth    r3, r3
  20:    2b00          cmp    r3, #0
  22:    d1f7          bne.n    14 <f+0x14>
  24:    8893          ldrh    r3, [r2, #4]
  26:    8813          ldrh    r3, [r2, #0]
  28:    07db          lsls    r3, r3, #31
  2a:    d4fc          bmi.n    26 <f+0x26>
  2c:    f44f 7280     mov.w    r2, #256    ; 0x100
  30:    8813          ldrh    r3, [r2, #0]
  32:    f003 0302     and.w    r3, r3, #2
  36:    b29b          uxth    r3, r3
  38:    2b00          cmp    r3, #0
  3a:    d1f9          bne.n    30 <f+0x30>
  3c:    f44f 7380     mov.w    r3, #256    ; 0x100
  40:    889b          ldrh    r3, [r3, #4]
  42:    4770          bx    lr

[Bug c/53085] write to volatile struct member is missing on Cortex-M3

[unixoid2003 at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53085

--- Comment #2 from brag <unixoid2003 at mail dot ru> 2012-04-23 13:19:03 UTC ---
The simpler example:

struct aa{
    volatile unsigned short a;
};

struct aa AAmem;

void f(){
    AAmem.a=0xff;
    AAmem.a=0xff;
}

00000000 <_Z1fv>:
   0:    f240 0300     movw    r3, #0
   4:    f2c0 0300     movt    r3, #0
   8:    22ff          movs    r2, #255    ; 0xff
   a:    801a          strh    r2, [r3, #0]  ; <<--- one write here
   c:    4770          bx    lr
   e:    bf00          nop

There is one write but should be two.

Reads seems to work good:
struct aa{
    volatile unsigned short a;
};

#define AAmem ((struct aa *) 256)

void f(){
    int t;
    t=AAmem->a;
    t=AAmem->a;
}

00000000 <_Z1fv>:
   0:    f44f 7380     mov.w    r3, #256    ; 0x100
   4:    881a          ldrh    r2, [r3, #0]  ;<<---| two reads here
   6:    881b          ldrh    r3, [r3, #0]  ;<<---|
   8:    4770          bx    lr
   a:    bf00          nop


Simple volatile variable seems to work OK:
#define s (*((volatile unsigned short*)128))

void f(){
    s=0xff;
    s=0xff;
}

00000000 <_Z1fv>:
   0:    2380          movs    r3, #128    ; 0x80
   2:    22ff          movs    r2, #255    ; 0xff
   4:    801a          strh    r2, [r3, #0]   ;<<---| two writes here
   6:    801a          strh    r2, [r3, #0]   ;<<---|
   8:    4770          bx    lr
   a:    bf00          nop

[Bug c/53085] writes to volatile struct members is missing

[unixoid2003 at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53085

brag <unixoid2003 at mail dot ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|critical                    |normal

[Bug c/53085] writes to volatile struct members is missing

[amonakov at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53085

Alexander Monakov <amonakov at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amonakov at gcc dot gnu.org

--- Comment #3 from Alexander Monakov <amonakov at gcc dot gnu.org> 2012-04-23 15:18:52 UTC ---
See discussion of volatile members in non-volatile structs in bug 45472

[Bug c/53085] writes to volatile struct members is missing

[unixoid2003 at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53085

--- Comment #4 from brag <unixoid2003 at mail dot ru> 2012-04-24 12:27:29 UTC ---
Alexander Monakov, As for me it's ok to treat whole struct as non-volatile even
if it has a volatile members when doing smth like this:
struct ss0 a,b;
a=b;
a=b;

Simple example with class:
class aa{
    void f();
private:
    volatile int a;
};

void aa::f(){
    a=0xff;
    a=0xff;
}

arm-none-eabi-gcc -O2 -mcpu=cortex-m3 -mthumb -c test.cpp
gcc-4.6.1 compiled:
00000000 <_ZN2aa1fEv>:
   0:   23ff            movs    r3, #255        ; 0xff
   2:   6003            str     r3, [r0, #0]
   4:   6003            str     r3, [r0, #0]
   6:   4770            bx      lr
The code is right.

gcc-4.7.0 compiled:
00000000 <_ZN2aa1fEv>:
   0:   23ff            movs    r3, #255        ; 0xff
   2:   6003            str     r3, [r0, #0]
   4:   4770            bx      lr
   6:   bf00            nop

The code is wrong. It's not ok to write once 'volatile int a' member.

[Bug tree-optimization/53085] writes to volatile struct members is missing

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53085

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2012-04-24
          Component|c                           |tree-optimization
         AssignedTo|unassigned at gcc dot       |rguenth at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #5 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-04-24 13:06:40 UTC ---
Confirmed and mine.

[Bug tree-optimization/53085] writes to volatile struct members is missing

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53085

--- Comment #6 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-04-24 13:13:26 UTC ---
Patch that applies to all maintained branches (the bug is also in 4.5!)

Index: gcc/tree-ssa-pre.c
===================================================================
--- gcc/tree-ssa-pre.c  (revision 186760)
+++ gcc/tree-ssa-pre.c  (working copy)
@@ -4409,6 +4409,7 @@ eliminate (void)
             has the same value number as its rhs.  If so, the store is
             dead.  */
          else if (gimple_assign_single_p (stmt)
+                  && !gimple_has_volatile_ops (stmt)
                   && !is_gimple_reg (gimple_assign_lhs (stmt))
                   && (TREE_CODE (rhs) == SSA_NAME
                       || is_gimple_min_invariant (rhs)))

[Bug tree-optimization/53085] writes to volatile struct members is missing

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53085

--- Comment #7 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-04-24 14:41:59 UTC ---
Author: rguenth
Date: Tue Apr 24 14:41:49 2012
New Revision: 186764

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=186764
Log:
2012-04-24  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/53085
    * tree-ssa-pre.c (eliminate): Do not eliminate volatile redundant
    stores.

    * g++.dg/torture/pr53085.C: New testcase.

Added:
    trunk/gcc/testsuite/g++.dg/torture/pr53085.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-pre.c

[Bug tree-optimization/53085] writes to volatile struct members is missing

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53085

--- Comment #8 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-04-24 14:43:01 UTC ---
Author: rguenth
Date: Tue Apr 24 14:42:53 2012
New Revision: 186765

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=186765
Log:
2012-04-24  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/53085
    * tree-ssa-pre.c (eliminate): Do not eliminate volatile redundant
    stores.

    * g++.dg/torture/pr53085.C: New testcase.

Added:
    branches/gcc-4_7-branch/gcc/testsuite/g++.dg/torture/pr53085.C
Modified:
    branches/gcc-4_7-branch/gcc/ChangeLog
    branches/gcc-4_7-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_7-branch/gcc/tree-ssa-pre.c

[Bug tree-optimization/53085] [4.7/4.8 Regression] writes to volatile struct members is missing

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53085

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|                            |4.7.1
         Resolution|                            |FIXED
   Target Milestone|---                         |4.7.1
            Summary|writes to volatile struct   |[4.7/4.8 Regression] writes
                   |members is missing          |to volatile struct members
                   |                            |is missing
      Known to fail|                            |4.7.0

--- Comment #9 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-04-24 14:45:02 UTC ---
Fixed for 4.7.1.