[Bug c/61123] New: With LTO, -fno-short-enums is ignored, resulting in ABI mis-matching in linking.

[Bug c/61123] New: With LTO, -fno-short-enums is ignored, resulting in ABI mis-matching in linking.

[Hale.Wang at arm dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61123

            Bug ID: 61123
           Summary: With LTO, -fno-short-enums is ignored, resulting in
                    ABI mis-matching in linking.
           Product: gcc
           Version: lto
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Hale.Wang at arm dot com

I have two trivial source files

obj1.cc:
    int x(int y)
    {
        return y - 10;
    }

obj2.cc:
    int foo(int bar)
    {
        return bar*10;
    }

If I link them without -flto, link time optimization is not invoked, and I get
an object file marked as having int-sized enums:

    $ arm-none-eabi-g++ -fno-short-enums -mcpu=arm946e-s obj1.cc obj2.cc
-Wl,-Ur -o partial_link_result.o -nostdlib -Os
    $ arm-none-eabi-readelf -a partial_link_result.o | grep enum
      Tag_ABI_enum_size: int

But if I simply add -flto to the linker invocation, the output claims that it
has small enums:

    $ arm-none-eabi-g++ -fno-short-enums -mcpu=arm946e-s obj1.cc obj2.cc
-Wl,-Ur -o partial_link_result.o -nostdlib -Os -flto
    $ arm-none-eabi-readelf -a partial_link_result.o | grep enum
      Tag_ABI_enum_size: small

It sure looks to me like something removed `-fno-short-enums` from
`COLLECT_GCC_OPTIONS` during the LTO step. I have reproduced the same behavior
on several different gcc 4.8 distributions (Mentor's Sourcery 4.8.1, Ubuntu's
4.8.2, and now the gcc-arm-embedded 4.8.3).

(The commands above are from Bobby Moretti)

The reason is that: if we add -flto option, link time optimization is invoked.
And the lto need to call the function run_gcc(unsigned argc, char *argv[]) in
lto-wrapper.c. The options in *argv[] are filtered by the following commands:
    if(!(cl_options[option->opt_index].flags & (CL_COMMON | CL_TARGET |
CL_DRIVER | CL_LTO)))
      continue;
So all the options which do not belong to the
CL_COMMON|CL_TARGET|CL_DRIVER|CL_LTO groups will be ignored by LTO. And
-fno-short-enums is one of these options.

I think it is a bug of LTO. Because the option flag_short_enums can change the
enum size in the generated object file. We should allow the users to disable
this optimization as they like. 

I suggest we can add the option flag_short_enums to the CL_COMMON group(or
CL_LTO group, I am not sure which group is more reasonable). And I have
confirmed that this change works.

There are several other options that are similar with flag_short_enums which
may change the ABI interface. And these options may cause the similar failure
in LTO. So how should we deal with these options? Should we develop a new
option group which could not be ignored by LTO?

[Bug lto/61123] With LTO, -fno-short-enums is ignored, resulting in ABI mis-matching in linking.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61123

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |lto

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
All ABI changing options should be also enabled for LTO and they also deserve
handling in lto-opts.c (always stream, not only if explicitely set) and
lto-wrapper.c (diagnose mismatches and force a setting for the link stage).

At least enabling them for LTO is minimally required, like you suggest.

[Bug lto/61123] With LTO, -fno-short-enums is ignored, resulting in ABI mis-matching in linking.

[Hale.Wang at arm dot com]

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61123

--- Comment #2 from Hale Wang <Hale.Wang at arm dot com> ---
(In reply to Richard Biener from comment #1)
> All ABI changing options should be also enabled for LTO and they also deserve
> handling in lto-opts.c (always stream, not only if explicitely set) and
> lto-wrapper.c (diagnose mismatches and force a setting for the link stage).
> 
> At least enabling them for LTO is minimally required, like you suggest.


Hi Richard,

I was dealing with the fno-short-enum bug that LTO ignore the options of
fshort-enum and fshort-wchar(fshort-wchar is similar with fshort-enum). I tried
to fix this bug by adding these options to LTO group. And this solution works.

Right now, I am trying to add some test cases to report some error message for
these cases in the previous gcc versions. And these cases will be passed after
I add these options to LTO group.

For the option of fshort-enum, I catch the Tag_ABI_enum_size from the final
executable. And this test case can work very well now.

But for  the option of fshort-wchar, if I compile the source files without
"-flto" option, I can catch the Tag_ABI_PCS_wchar_t from the final executable.
If I add the "-flto" option to the compile command, the Tag_ABI_PCS_wchar_t is
totally disappeared in the final executable.

So I think this is another bug which means the final executable file (or the
ABI) is different if we add "-flto" or not. 

I generated a minimal example.I have two source files:

wchar_0.c:
         #include <stddef.h>                
         wchar_t         wc0[]=L”abc”;
         const wchar_t   wc1[]=L”abc”; 

wchar_1.c:
         #include <stddef.h>                
         wchar_t               b0[]={ L”abc” };
         const wchar_t   b1[]={ L”abc” }; 

Firstly, I compile these files without “-flto”:

$ arm-none-eabi-gcc  -fshort-wchar  wchar_0.c  wchar_1.c  -Wl,-Ur  -o 
without_flto.o  -nostdlib  -Os
$ arm-none-eabi-readelf  -A  without_flto.o

Attribute Section: aeabi
File Attributes
  Tag_CPU_name: "ARM7TDMI"
  Tag_CPU_arch: v4T
  Tag_ARM_ISA_use: Yes
  Tag_THUMB_ISA_use: Thumb-1
  Tag_ABI_PCS_wchar_t: 2
  Tag_ABI_FP_denormal: Needed
  Tag_ABI_FP_exceptions: Needed
  Tag_ABI_FP_number_model: IEEE 754
  Tag_ABI_align_needed: 8-byte
  Tag_ABI_align_preserved: 8-byte, except leaf SP
  Tag_ABI_enum_size: small
  Tag_ABI_optimization_goals: Aggressive Size


Then I compile these files with –flto:

$ arm-none-eabi-gcc  -fshort-wchar  wchar_0.c  wchar_1.c  -Wl,-Ur  -o 
with_flto.o  -nostdlib  -Os –flto
$ arm-none-eabi-readelf  -A  with_flto.o

Attribute Section: aeabi
File Attributes
  Tag_CPU_name: "ARM7TDMI"
  Tag_CPU_arch: v4T
  Tag_ARM_ISA_use: Yes
  Tag_THUMB_ISA_use: Thumb-1
  Tag_ABI_FP_denormal: Needed
  Tag_ABI_FP_exceptions: Needed
  Tag_ABI_FP_number_model: IEEE 754
  Tag_ABI_align_needed: 8-byte
  Tag_ABI_align_preserved: 8-byte, except leaf SP
  Tag_ABI_enum_size: small
  Tag_ABI_optimization_goals: Aggressive Size

So we can see the Tag_ABI_PCS_wchar_t attribute is totally disappeared. 

What do you think about this?
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From: "Joost.VandeVondele at mat dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/61335] New: [4.10 Regression] wrong code with -O2 -fbounds-check
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ida335

            Bug ID: 61335
           Summary: [4.10 Regression] wrong code with -O2 -fbounds-check
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Joost.VandeVondele at mat dot ethz.ch

Created attachment 32868
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id2868&actioníit
reduced testcase

The attached testcase is miscompiled with current trunk. A recent regression
caused in the day between good: r210955 and bad: r210994

To reproduce compile and run the attached testcase as :

> gfortran -O2 -fbounds-check cp_units.f90 ; ./a.out
 BUG : XXXfs^-1XXX integer expected
STOP 1

while e.g. '-O2' alone or '-fbound-check -O1' work fine.

[Bug lto/61123] With LTO, -fno-short-enums is ignored, resulting in ABI mis-matching in linking.

[Hale.Wang at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61123

--- Comment #4 from Hale Wang <Hale.Wang at arm dot com> ---
(In reply to Richard Biener from comment #3)
> It seems that Tag_ABI_PCS_wchar_t is emitted from the C-family frontends only
> via config/arm/arm-c.c (as opposed to any other Tags).  Probably because
> the option is c-family specific.  This code needs to move to generic handling
> (the option enum is shared across all frontends, so that's not a reason to
> keep it in a C specific file).

Thanks very much for your comments. So this seems to be a separate issue that
the Tag_ABI_PCS_wchar_t need to be moved to LTO frontend at least,but not only
the C frontend. May be I need to creat another patch or bug description for
this issue.

[Bug lto/61123] With LTO, -fno-short-enums is ignored, resulting in ABI mis-matching in linking.

[zqchen at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61123

--- Comment #5 from zqchen at gcc dot gnu.org ---
Author: zqchen
Date: Fri Jun 20 04:52:11 2014
New Revision: 211832

URL: https://gcc.gnu.org/viewcvs?rev=211832&root=gcc&view=rev
Log:
c-family/ChangeLog
2014-06-20 Hale Wang <hale.wang@arm.com>

    PR lto/61123
    * c.opt (fshort-enums): Add to LTO.
    * c.opt (fshort-wchar): Likewise.

testsuite/ChangeLog
2014-06-20 Hale Wang <hale.wang@arm.com>

    * gcc.target/arm/lto/: New folder to verify the LTO option.
    * gcc.target/arm/lto/pr61123-enum-size_0.c: New test case.
    * gcc.target/arm/lto/pr61123-enum-size_1.c: Likewise.
    * gcc.target/arm/lto/lto.exp: New exp file used to test LTO option.
    * lib/lto.exp (object-readelf): New procedure.

Added:
    trunk/gcc/testsuite/gcc.target/arm/lto/
    trunk/gcc/testsuite/gcc.target/arm/lto/lto.exp
    trunk/gcc/testsuite/gcc.target/arm/lto/pr61123-enum-size_0.c
    trunk/gcc/testsuite/gcc.target/arm/lto/pr61123-enum-size_1.c
Modified:
    trunk/gcc/c-family/ChangeLog
    trunk/gcc/c-family/c.opt
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/lib/lto.exp

[Bug lto/61123] With LTO, -fno-short-enums is ignored, resulting in ABI mis-matching in linking.

[Hale.Wang at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61123

--- Comment #6 from Hale Wang <Hale.Wang at arm dot com> ---
Thanks for Zhenqiang Chen's help. This bug is fixed. Refer to the link
https://gcc.gnu.org/ml/gcc-patches/2014-06/msg01429.html

[Bug lto/61123] With LTO, -fno-short-enums is ignored, resulting in ABI mis-matching in linking.

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61123

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

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

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.

[Bug lto/61123] With LTO, -fno-short-enums is ignored, resulting in ABI mis-matching in linking.

[xguo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61123

--- Comment #8 from xuepeng guo <xguo at gcc dot gnu.org> ---
Author: xguo
Date: Tue Jul 29 07:11:02 2014
New Revision: 213147

URL: https://gcc.gnu.org/viewcvs?rev=213147&root=gcc&view=rev
Log:
gcc/c-family/
2014-07-29  Terry Guo  <terry.guo@arm.com>

    Backport mainline r211832
    2014-06-20  Hale Wang  <hale.wang@arm.com>

    PR lto/61123
    * c.opt (fshort-enums): Add to LTO.
    * c.opt (fshort-wchar): Likewise.

gcc/testsuite/
2014-07-29  Terry Guo  <terry.guo@arm.com>

    Backport mainline r211832
    2014-06-20  Hale Wang  <hale.wang@arm.com>

    * gcc.target/arm/lto/: New folder to verify the LTO option.
    * gcc.target/arm/lto/pr61123-enum-size_0.c: New test case.
    * gcc.target/arm/lto/pr61123-enum-size_1.c: Likewise.
    * gcc.target/arm/lto/lto.exp: New exp file used to test LTO option.
    * lib/lto.exp (object-readelf): New procedure.

Added:
    branches/ARM/embedded-4_8-branch/gcc/c-family/ChangeLog.arm
    branches/ARM/embedded-4_8-branch/gcc/testsuite/gcc.target/arm/lto/
    branches/ARM/embedded-4_8-branch/gcc/testsuite/gcc.target/arm/lto/lto.exp
   
branches/ARM/embedded-4_8-branch/gcc/testsuite/gcc.target/arm/lto/pr61123-enum-size_0.c
   
branches/ARM/embedded-4_8-branch/gcc/testsuite/gcc.target/arm/lto/pr61123-enum-size_1.c
Modified:
    branches/ARM/embedded-4_8-branch/gcc/c-family/c.opt
    branches/ARM/embedded-4_8-branch/gcc/testsuite/ChangeLog.arm
    branches/ARM/embedded-4_8-branch/gcc/testsuite/lib/lto.exp