Ping?
I'd also like to backport this and the main patch (svn r279463,
r10-5505-ge24f6408df1e4c5e8c09785d7b488c492dfb68b3)
to the gcc-9 branch.
I found the problem addressed by this patch while validating the
backport to gcc-9: although the patch applies cleanly except for
testcases dg directives, there were some failures which I could
finally reproduce on trunk with -fdisable-rtl-fwprop2.
Here is a summary of the validations I ran using --target arm-eabi:
* without my patches:
(1) --with-cpu cortex-m0
(2) --with-cpu cortex-m4
(3) --with-cpu cortex-m4 CFLAGS_FOR_TARGET=-mpure-code (to build the
libs with -mpure-code)
(4) --with-cpu cortex-m4 CFLAGS_FOR_TARGET=-mpure-code
--target-board=-mpure-code (to also run the tests with -mpure-code)
* with my patches:
(5) --with-cpu cortex-m0 CFLAGS_FOR_TARGET=-mpure-code
--target-board=-mpure-code
(6) --with-cpu cortex-m4 CFLAGS_FOR_TARGET=-mpure-code
--target-board=-mpure-code
Comparing (4) and (6) ensured that my (v6m) patches introduce no
regression in v7m cases.
Comparison of (1) vs (5) gave results similar to (2) vs (6), there's a
bit of noise because some tests cases don't cope well with -mpure-code
despite my previous testsuite-only patch (svn r277828)
Comparison of (1) vs (2) gave similar results to (5) vs (6).
Ideally, we may also want to backport svn r277828 (testsuite-only
patch, to handle -mpure-code better), but that's not mandatory.
In summary, is this patch OK for trunk?
Are this patch and r279463,
r10-5505-ge24f6408df1e4c5e8c09785d7b488c492dfb68b3 OK to backport to
gcc-9?
Thanks,
Christophe
On Thu, 13 Feb 2020 at 11:14, Christophe Lyon
<christophe.l...@linaro.org> wrote:
>
> On Mon, 10 Feb 2020 at 17:45, Richard Earnshaw (lists)
> <richard.earns...@arm.com> wrote:
> >
> > On 10/02/2020 09:27, Christophe Lyon wrote:
> > > On Fri, 7 Feb 2020 at 17:55, Richard Earnshaw (lists)
> > > <richard.earns...@arm.com> wrote:
> > >>
> > >> On 07/02/2020 16:43, Christophe Lyon wrote:
> > >>> On Fri, 7 Feb 2020 at 14:49, Richard Earnshaw (lists)
> > >>> <richard.earns...@arm.com> wrote:
> > >>>>
> > >>>> On 07/02/2020 13:19, Christophe Lyon wrote:
> > >>>>> When running the testsuite with -fdisable-rtl-fwprop2 and -mpure-code
> > >>>>> for cortex-m0, I noticed that some testcases were failing because we
> > >>>>> still generate "ldr rX, .LCY", which is what we want to avoid with
> > >>>>> -mpure-code. This is latent since a recent improvement in fwprop
> > >>>>> (PR88833).
> > >>>>>
> > >>>>> In this patch I change the thumb1_movsi_insn pattern so that it emits
> > >>>>> the desired instruction sequence when arm_disable_literal_pool is set.
> > >>>>>
> > >>>>> I tried to add a define_split instead, but couldn't make it work: the
> > >>>>> compiler then complains it cannot split the instruction, while my new
> > >>>>> define_split accepts the same operand types as thumb1_movsi_insn:
> > >>>>>
> > >>>>> c-c++-common/torture/complex-sign-mixed-add.c:41:1: error: could not
> > >>>>> split insn
> > >>>>> (insn 2989 425 4844 (set (reg/f:SI 3 r3 [1342])
> > >>>>> (symbol_ref/u:SI ("*.LC6") [flags 0x2])) 836
> > >>>>> {*thumb1_movsi_insn}
> > >>>>> (expr_list:REG_EQUIV (symbol_ref/u:SI ("*.LC6") [flags 0x2])
> > >>>>> (nil)))
> > >>>>> during RTL pass: final
> > >>>>>
> > >>>>> (define_split
> > >>>>> [(set (match_operand:SI 0 "register_operand" "")
> > >>>>> (match_operand:SI 1 "general_operand" ""))]
> > >>>>> "TARGET_THUMB1
> > >>>>> && arm_disable_literal_pool
> > >>>>> && GET_CODE (operands[1]) == SYMBOL_REF"
> > >>>>> [(clobber (const_int 0))]
> > >>>>> "
> > >>>>> gen_thumb1_movsi_symbol_ref(operands[0], operands[1]);
> > >>>>> DONE;
> > >>>>> "
> > >>>>> )
> > >>>>> and I put this in thumb1_movsi_insn:
> > >>>>> if (GET_CODE (operands[1]) == SYMBOL_REF && arm_disable_literal_pool)
> > >>>>> {
> > >>>>> return \"#\";
> > >>>>> }
> > >>>>> return \"ldr\\t%0, %1\";
> > >>>>>
> > >>>>> 2020-02-07 Christophe Lyon <christophe.l...@linaro.org>
> > >>>>>
> > >>>>> * config/arm/thumb1.md (thumb1_movsi_insn): Fix ldr
> > >>>>> alternative to
> > >>>>> work with -mpure-code.
> > >>>>>
> > >>>>
> > >>>> + case 0:
> > >>>> + case 1:
> > >>>> + return \"movs %0, %1\";
> > >>>> + case 2:
> > >>>> + return \"movw %0, %1\";
> > >>>>
> > >>>> This is OK, but please replace the hard tab in the strings for
> > >>>> MOVS/MOVW
> > >>>> with \\t.
> > >>>>
> > >>>
> > >>> OK that was merely a cut & paste from the existing code.
> > >>>
> > >>> I'm concerned that the length attribute is becoming wrong with my
> > >>> patch, isn't this a problem?
> > >>>
> > >>
> > >> Potentially yes. The branch range code needs this to handle overly long
> > >> jumps correctly.
> > >>
> > >
> > > Do you mean that the probability of problems due to that shortcoming
> > > is low enough that I can commit my patch?
> >
> > It's hard to say that. The number of instructions you generate for this
> > is significant, so it likely will throw off the calculations and
> > somebody will get unlucky. On the other hand, I don't think we should
> > pessimize code for the non-pure-code variants by inflating the size for
> > this unconditionally.
> >
> > It seems there are two ways to fix this.
> >
> > 1) create a new alternative for the pure-code variant with its own
> > length attribute, then only enable that for the case you need. That
> > would also allow you to go back to the templated asm format.
> > 2) use a level of indirection to calculate the length - I haven't tried
> > this, but it would be something like:
> >
> > - create a new attribute - lets say default_length
> > - rename length for this pattern to default_length
> > - create another new attribute - lets say purecode_length, add lengths
> > for each alternative but adjusted for the purecode variant.
> > - make the length attribute for this pattern select based on the
> > disable_literal_pool variable between the default_length and
> > purecode_length attributes.
> >
>
> Hi Richard,
>
> Thanks for the suggestions. I've implemented option (1) above, does
> it match what you had in mind?
>
> Tested on arm-eabi, with -mpure-code forced, no regression. Manually
> checked that the expected sequence is generated with
> -fdisable-rtl-fwprop2.
>
> Thanks,
>
> Christophe
>
> > R.
> >
> > >
> > > Thanks,
> > >
> > > Christophe
> > >
> > >> R.
> > >>
> > >>> Thanks,
> > >>>
> > >>> Christophe
> > >>>
> > >>>> R.
> > >>
> >
