[Bug inline-asm/10396] Constraint alternatives cause error " `asm' operand requires impossible reload"

[bernd.edlinger at hotmail dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10396

Bernd Edlinger  changed:

   What|Removed |Added

 CC||bernd.edlinger at hotmail dot 
de

--- Comment #23 from Bernd Edlinger  ---
(In reply to David from comment #22)
> Despite the impression you may get from comments 17-21, gcc DOES support
> multi-alternatives with inline asm (see
> https://gcc.gnu.org/ml/gcc/2015-10/msg00249.html).
> 
> I do not have an arm build with which to test, but using 5.2 on x64, the
> samples in this bug do not produce errors.  Perhaps in the 7-12 years since
> they were added, something got fixed?  Or maybe this problem is
> platform-specific.

you can build a cross-compiler out of nothing, if you want.

cd binutils-build-arm
../binutils-2.25.1/configure --prefix=../arm-eabi --target=arm-unknown-eabi
make && make install
cd ../gcc-build-arm
../gcc-trunk/configure --prefix=/home/ed/gnu/arm-eabi --target=arm-unknown-eabi
--enable-languages=c --disable-libssp
make && make install

[Bug inline-asm/10396] Constraint alternatives cause error " `asm' operand requires impossible reload"

[gccbugzilla at limegreensocks dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10396

David  changed:

   What|Removed |Added

 CC||gccbugzilla@limegreensocks.
   ||com

--- Comment #22 from David  ---
Despite the impression you may get from comments 17-21, gcc DOES support
multi-alternatives with inline asm (see
https://gcc.gnu.org/ml/gcc/2015-10/msg00249.html).

I do not have an arm build with which to test, but using 5.2 on x64, the
samples in this bug do not produce errors.  Perhaps in the 7-12 years since
they were added, something got fixed?  Or maybe this problem is
platform-specific.

[Bug inline-asm/10396] Constraint alternatives cause error `asm' operand requires impossible reload

[someone42 at gmail dot com]

--- Comment #18 from someone42 at gmail dot com  2008-12-31 16:05 ---
I was going to submit a new bug report but this bug sounds very similar. Here
is my test case:

Code (actual assembly code removed for brevity):
int thing(unsigned int a,unsigned int b)
{
  asm(:=mr,r(b):%0,0(a / 3),ri,g(b));
  return b;
}

Result:
$ gcc aorir.c -S -O1
aorir.c: In function 'thing':
aorir.c:3: error: 'asm' operand requires impossible reload

This was tested with GCC 4.3.2 and only occurs if -O, -O1, -O2, -O3 or -Os is
used. Like the opening poster, this only occurs if multiple alternatives are
specified. Removing one of the alternatives makes the issue disappear (it does
not matter which one is removed). Replacing a / 3 with a + 3 also makes the
issue disappear, regardless of the number of alternatives specified. Removing
% from the first input constraint results in:

$ gcc aorir.c -S -O1
aorir.c: In function 'thing':
aorir.c:5: internal compiler error: in reg_overlap_mentioned_p, at
rtlanal.c:1398
Please submit a full bug report,
with preprocessed source if appropriate.
See http://gcc.gnu.org/bugs.html for instructions.

Changing %0,0 to %r,r also makes the issue go away, however that is not an
option for the assembly code I'm using.


-- 

someone42 at gmail dot com changed:

   What|Removed |Added

 CC||someone42 at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10396

[Bug inline-asm/10396] Constraint alternatives cause error `asm' operand requires impossible reload

[pinskia at gcc dot gnu dot org]

--- Comment #19 from pinskia at gcc dot gnu dot org  2008-12-31 16:09 
---
Note commas in inline-asm are ignored.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10396

[Bug inline-asm/10396] Constraint alternatives cause error `asm' operand requires impossible reload

[someone42 at gmail dot com]

--- Comment #20 from someone42 at gmail dot com  2008-12-31 16:29 ---
(In reply to comment #19)
 Note commas in inline-asm are ignored.
 

Perhaps this bug could then be fixed by simply removing or appropriately
modifying section 5.38.2 (Multiple Alternative Constraints) of the GCC
manual.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10396

[Bug inline-asm/10396] Constraint alternatives cause error `asm' operand requires impossible reload

[pinskia at gcc dot gnu dot org]

--- Comment #21 from pinskia at gcc dot gnu dot org  2008-12-31 16:36 
---
(In reply to comment #20) 
 Perhaps this bug could then be fixed by simply removing or appropriately
 modifying section 5.38.2 (Multiple Alternative Constraints) of the GCC
 manual.

Part of the problem is that section is part of the internals manual also and
alternative constraints works correctly for RTL, just not inline-asm.  For some
reason I thought it was already patched to say the correct thing. 


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10396