[Bug bootstrap/65733] New: gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[Bug bootstrap/65733] New: gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65733

            Bug ID: 65733
           Summary: gcc 4.9.2 suffers bootstrap comparison failures with
                    clang 3.5.1 and later.
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: bootstrap
          Assignee: unassigned at gcc dot gnu.org
          Reporter: howarth.at.gcc at gmail dot com

The Xcode 6.3 release (with Apple Clang 6.1 compilers based on 3.6.0svn)
produces bootstrap comparison failures in the gcc 4.9.2 build on
x86_64-apple-darwin14. The same bootstrap comparison failure is also seen on
x86_64-apple-darwin13 with Xcode 6.2 but using the llvm.org clang 3.5.1, 3.5.2
or 3.6.0 compilers instead of the Apple Clang 6.0 compilers.

Comparing stages 2 and 3
warning: gcc/cc1-checksum.o differs
warning: gcc/cc1obj-checksum.o differs
warning: gcc/cc1objplus-checksum.o differs
warning: gcc/cc1plus-checksum.o differs
Bootstrap comparison failure!
gcc/asan.o differs
gcc/attribs.o differs
gcc/bitmap.o differs
gcc/c/c-decl.o differs
gcc/cfg.o differs
gcc/coverage.o differs
gcc/cp/class.o differs
gcc/cp/semantics.o differs
gcc/cp/tree.o differs
gcc/dse.o differs
gcc/dwarf2out.o differs
gcc/except.o differs
gcc/fortran/trans-common.o differs
gcc/ggc-common.o differs
gcc/graphite-clast-to-gimple.o differs
gcc/graphite.o differs
gcc/ipa-profile.o differs
gcc/ira-color.o differs
gcc/ira-costs.o differs
gcc/java/jcf-io.o differs
gcc/loop-unroll.o differs
gcc/lto-streamer-in.o differs
gcc/lto-streamer-out.o differs
gcc/objc/objc-act.o differs
gcc/objcp/objcp-act.o differs
gcc/passes.o differs
gcc/plugin.o differs
gcc/postreload-gcse.o differs
gcc/statistics.o differs
gcc/trans-mem.o differs
gcc/tree-cfg.o differs
gcc/tree-eh.o differs
gcc/tree-ssa-ccp.o differs
gcc/tree-ssa-coalesce.o differs
gcc/tree-ssa-dom.o differs
gcc/tree-ssa-live.o differs
gcc/tree-ssa-loop-ivopts.o differs
gcc/tree-ssa-phiopt.o differs
gcc/tree-ssa-pre.o differs
gcc/tree-ssa-reassoc.o differs
gcc/tree-ssa-threadupdate.o differs
gcc/tree-ssa-uncprop.o differs
gcc/tree-vectorizer.o differs
gcc/valtrack.o differs
gcc/vtable-verify.o differs
Makefile:20180: recipe for target 'compare' failed

The observation, that the llvm.org clang 3.5.1 or later compilers along side
Xcode 6.2 produces the same bootstrap comparison failure, eliminates the
cctools changes in Xcode 6.3 as the culprit and points to miscompilation of the
stage1 compiler instead.

Reducing the optimization of the stage1 bootstrap with STAGE1_CFLAGS="-O0 -g"
and STAGE1_CXXFLAGS="-O0 -g" doesn't eliminate the bootstrap comparison
failure.

Interestingly, current gcc trunk 5.0svn doesn't exhibit the bootstrap
comparison failure (with the stock build or using --enable-checking=release).

[Bug bootstrap/65733] gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65733

--- Comment #1 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
Gcc bootstraps were all tested with...

../gcc-4.9.2/configure --prefix=/sw --prefix=/sw/lib/gcc4.9
--mandir=/sw/share/man --infodir=/sw/lib/gcc4.9/info
--enable-languages=c,c++,fortran,lto,objc,obj-c++,java --with-gmp=/sw
--with-libiconv-prefix=/sw --with-isl=/sw --with-cloog=/sw --with-mpc=/sw
--with-system-zlib --x-includes=/usr/X11R6/include --x-libraries=/usr/X11R6/lib
--program-suffix=-fsf-4.9

The stock Apple clang 6.0 compilers from Xcode 6.2 don't exhibit the bootstrap
comparison failure of course on either x86_64-apple-darwin13 or
x86_64-apple-darwin14.

[Bug bootstrap/65733] gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65733

--- Comment #2 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
Current gcc-4_9-branch at r221965 suffers the same bootstrap comparison failure
on x86_64-apple-darwin14 with Xcode 6.3's Apple Clang 6.1 compilers and on
x86_64-apple-darwin13 with Xcode 6.2 and the llvm.org 3.6.0's clang compilers.

[Bug bootstrap/65733] gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65733

--- Comment #3 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
As Iain pointed out to me, the gcc configure output under the more recent clang
compilers isn't setting BUILD_CONFIG. Oddly gcc trunk also doesn't set
BUILD_CONFIG in the configure output under the more recent clang compilers but
the bootstrap comparison failure isn't seen. For gcc 4.9 and gcc-4_9-branch,
--with-build-config=bootstrap-debug  has to be explicitly passed to configure
to suppress the bootstrap comparison failures under the more recent clang
compilers.

[Bug bootstrap/65733] gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65733

--- Comment #4 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
The issue in configure can be seen with...

mkdir conftest
cd conftest
echo "int f (void) { return 0; }" > conftest.c
clang-3.6 -c conftest.c
mv conftest.o conftest.o.g0
clang-3.6 -c -g conftest.c
mv conftest.o conftest.o.g
../gcc-4.9.3-20150410/contrib/compare-debug conftest.o.g0 conftest.o.g

..which unexpectedly produces...

conftest.o.g0.stripped conftest.o.g.stripped differ: char 433, line 1
stripping off .eh_frame and LTO sections, then retrying
failed to strip off .eh_frame
conftest.o.g0.stripped conftest.o.g.stripped differ: char 433, line 1

[Bug bootstrap/65733] gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65733

--- Comment #5 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
Created attachment 35295
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35295&action=edit
binary conftest.o.g from clang 3.6.0 compiler

The binary conftest.o.g was created on x86_64-apple-darwin13 using the cctools
from Xcode 6.2 and the llvm.org 3.6.0 clang compilers with the command...

echo "int f (void) { return 0; }" > conftest.c
clang-3.6 -c -g conftest.c
mv conftest.o conftest.o.g

[Bug bootstrap/65733] gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65733

--- Comment #6 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
Created attachment 35296
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35296&action=edit
binary conftest.o.g0 from clang 3.6.0 compiler

The binary conftest.o.g was created on x86_64-apple-darwin13 using the cctools
from Xcode 6.2 and the llvm.org 3.6.0 clang compilers with the command...

echo "int f (void) { return 0; }" > conftest.c
clang-3.6 -c conftest.c
mv conftest.o conftest.o.g0

[Bug bootstrap/65733] gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65733

--- Comment #7 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
Using...

ld -S -r -no_uuid conftest.o.g -o conftest.o.g.stripped
ld -S -r -no_uuid conftest.o.g0 -o conftest.o.g0.stripped
dwarfdump --eh-frame conftest.o.g.stripped > conftest.o.g.stripped.dwarfdump
dwarfdump --eh-frame conftest.o.g0.stripped > conftest.o.g0.stripped.dwarfdump

for conftest.c compiled with Xcode 6.2 Apple Clang 6.0 on
x86_64-apple-darwin13, we get...

% diff -u conftest.o.g.stripped.dwarfdump conftest.o.g0.stripped.dwarfdump
--- conftest.o.g.stripped.dwarfdump    2015-04-10 21:43:15.000000000 -0400
+++ conftest.o.g0.stripped.dwarfdump    2015-04-10 21:43:04.000000000 -0400
@@ -1,5 +1,5 @@
 ----------------------------------------------------------------------
- File: conftest.o.g.stripped (x86_64)
+ File: conftest.o.g0.stripped (x86_64)
 ----------------------------------------------------------------------
 Exception handling frame information for section __eh_frame


but for contest.c compiled with llvm.org 3.6.0's clang on
x86_64-apple-darwin13, we get...

% diff -u conftest.o.g.stripped.dwarfdump conftest.o.g0.stripped.dwarfdump
--- conftest.o.g.stripped.dwarfdump    2015-04-10 21:42:02.000000000 -0400
+++ conftest.o.g0.stripped.dwarfdump    2015-04-10 21:41:52.000000000 -0400
@@ -1,12 +1,12 @@
 ----------------------------------------------------------------------
- File: conftest.o.g.stripped (x86_64)
+ File: conftest.o.g0.stripped (x86_64)
 ----------------------------------------------------------------------
 Exception handling frame information for section __eh_frame

 0x00000000: CIE
         length: 0x00000014
         CIE_id: 0xffffffff
-       version: 0x01
+       version: 0x03
   augmentation: "zR"
     code_align: 1
     data_align: -8

[Bug bootstrap/65733] gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65733

Iain Sandoe <iains at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #8 from Iain Sandoe <iains at gcc dot gnu.org> ---
(In reply to Jack Howarth from comment #7)

> % diff -u conftest.o.g.stripped.dwarfdump conftest.o.g0.stripped.dwarfdump
> --- conftest.o.g.stripped.dwarfdump	2015-04-10 21:42:02.000000000 -0400
> +++ conftest.o.g0.stripped.dwarfdump	2015-04-10 21:41:52.000000000 -0400
> @@ -1,12 +1,12 @@
>  ----------------------------------------------------------------------
> - File: conftest.o.g.stripped (x86_64)
> + File: conftest.o.g0.stripped (x86_64)
>  ----------------------------------------------------------------------
>  Exception handling frame information for section __eh_frame
>  
>  0x00000000: CIE
>          length: 0x00000014
>          CIE_id: 0xffffffff
> -       version: 0x01
> +       version: 0x03

Confirmed with TOT clang as of this morning.  Please file an llvm BZ and/or a
radar against Xcode 6.3.
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From: "dominiq at lps dot ens.fr" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug bootstrap/65733] gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.
Date: Sat, 11 Apr 2015 09:39:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ide733

--- Comment #9 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
Same problem with 4.8.5.

[Bug bootstrap/65733] gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65733

--- Comment #10 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
> 
> Confirmed with TOT clang as of this morning.  Please file an llvm BZ and/or
> a radar against Xcode 6.3.

Reported as radar bug /20509942, "Apple Clang 6.1 emits inconsistent eh_frame
dwarf versions"

[Bug bootstrap/65733] gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65733

--- Comment #11 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
This issue appears to have been introduced by...

http://llvm.org/viewvc/llvm-project?view=revision&revision=211272

and seems to have been previously discussed...

http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20141208/247970.html

[Bug bootstrap/65733] gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65733

--- Comment #12 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
It appears that clang 3.5 and later defaults to setting the CIE version to
dwarf2 in the absence of -g. This behavior can't be overridden by passing
-gdwarf-3 in the absence of -g. However the gcc configure test failure can be
suppressed under clang by appending -gdwarf-2 instead (to downgrade the CIE
version to dwarf3 in the presence of -g).