rs6000: Disable generation of lwa in 32-bit mode

Many (most? all?) assemblers (and really the 32-bit ABIs) do not handle
lwa and ld properly.  Those instructions have a 14-bit offset field, and
the low two bits of the instruction are the extended opcode.  But the
32-bit toolchains use a 16-bit offset relocation, clobbering the low
two bits.  See PR27619 and binutils #14758.

This works out fine for the most common case (word-aligned ld), but not
for most others.  This patch disables all lwa insns in 32-bit mode.
We can later re-enable it if the assembler used handles it properly,
and for lwax and lwaux, and fix the various ld patterns as well, but
this is at least a small step in the right direction.

gcc:
-# of expected passes           108499
-# of unexpected failures       303
+# of expected passes           108508
+# of unexpected failures       295

gfortran:
-# of expected passes           40555
-# of unexpected failures       175
+# of expected passes           40582
+# of unexpected failures       148

The lwa pattern must be below the extsw pattern, because the lwa_operand
predicate allows registers as well.  Changing lwa_operand causes other
problems I do not want to deal with right now.

Bootstrapped and tested on powerpc64-linux -m64,-m32,-m32/-mpowerpc64.

Okay to apply?


Segher


2012-10-25  Segher Boessenkool  <segher@kernel.crashing.org>

gcc/
	* config/rs6000/rs6000.md (sign_extend:SI patterns): Split
	the memory case off.  Merge the two register cases.  Change
	the condition for the memory case to require 64-bit mode.

---
 gcc/config/rs6000/rs6000.md |   22 ++++++++++++----------
 1 files changed, 12 insertions(+), 10 deletions(-)

On Thu, Oct 25, 2012 at 6:57 PM, Segher Boessenkool
<segher@kernel.crashing.org> wrote:

> 2012-10-25  Segher Boessenkool  <segher@kernel.crashing.org>
>
> gcc/
>         * config/rs6000/rs6000.md (sign_extend:SI patterns): Split
>         the memory case off.  Merge the two register cases.  Change
>         the condition for the memory case to require 64-bit mode.

This is okay.

Thanks, David

On Thu, Oct 25, 2012 at 03:57:38PM -0700, Segher Boessenkool wrote:
> for most others.  This patch disables all lwa insns in 32-bit mode.
> We can later re-enable it if the assembler used handles it properly,

Well, you can now do that.  Mainline gas and ld are now fixed.

On Fri, 2012-10-26 at 15:00 +1030, Alan Modra wrote:
> On Thu, Oct 25, 2012 at 03:57:38PM -0700, Segher Boessenkool wrote:
> > for most others.  This patch disables all lwa insns in 32-bit mode.
> > We can later re-enable it if the assembler used handles it properly,
> 
> Well, you can now do that.  Mainline gas and ld are now fixed.

Now that gas and ld are fixed, can we use a configure time check to
see whether we're using a fixed gas/ld or not before we disable them?

Peter

>>> for most others.  This patch disables all lwa insns in 32-bit mode.
>>> We can later re-enable it if the assembler used handles it properly,
>>
>> Well, you can now do that.  Mainline gas and ld are now fixed.

Yes, you are much too quick for me to keep up.  Thank you!

> Now that gas and ld are fixed, can we use a configure time check to
> see whether we're using a fixed gas/ld or not before we disable them?

When I wrote this patch, I thought the Darwin assembler had the same
problem.  No idea how I got that in my mind; it doesn't.  And AIX does
not support -m32 -mpowerpc64 at all (the compiler disallows it), so
that is out of the picture as well.

I now bootstrapped and tested with the new binutils.  Most of the
testcases that were fixed with my patch are fixed there as well; and
some (20040709-2.c, etc.) fail with a linker error now, instead of
the runtime error.  Some fail that passed without either patch, but
failing is correct -- wrong code sometimes runs fine :-)

So I'm not applying this patch.  I don't think we need a configure
check: we have had many releases with these bugs already, one more
won't hurt.  People generally use a recent version of binutils as well.


Segher