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Re: [PATCH] Fix PR rtl-optimization/61278


On 23 May 2014 17:05, Richard Biener <richard.guenther@gmail.com> wrote:
> On Fri, May 23, 2014 at 9:23 AM, Zhenqiang Chen
> <zhenqiang.chen@linaro.org> wrote:
>> Hi,
>>
>> The patch fixes PR rtl-optimization/61278. Root cause for issue is
>> that df_live does not exist at -O1.
>>
>> Bootstrap and no make check regression on X86-64.
>>
>> OK for trunk?
>
> Why do you need to give up?  It seems you can simply avoid
> marking the block as dirty (though df_get_live_in/out also hands you
> back DF_LR_IN/OUT if !df_live).  So isn't the df_grow_bb_info the
> "real" fix?

The df_get_live_in of the new basic block will be used to analyse
later INSNs. If it is not set or incorrect, it will impact on later
analysis.
df_grow_bb_info is to make sure the live_in data structure is
allocated for the new basic block (although I have not found any case
fail without it). After bitmap_copy(...), we can use it for later
INSNs.

> Note that df_get_live_in/out are functions tailored to IRA that
> knows that they handle both df_live and df_lr dependent on
> optimization level.  Is shrink-wrapping supposed to work with
> both problems as well?

Yes. But it seams not perfect to handle df_lr problem. When I fixed PR
57637 (https://gcc.gnu.org/ml/gcc-patches/2013-07/msg00897.html), we
selected "if DF_LIVE doesn't exist, i.e. at -O1, just give up
searching NEXT_BLOCK."

Thanks!
-Zhenqiang

>>
>> ChangeLog:
>> 2014-05-23  Zhenqiang Chen  <zhenqiang.chen@linaro.org>
>>
>>         PR rtl-optimization/61278
>>         * shrink-wrap.c (move_insn_for_shrink_wrap): Check df_live.
>>
>> testsuite/ChangeLog:
>> 2014-05-23  Zhenqiang Chen  <zhenqiang.chen@linaro.org>
>>
>>         * gcc.dg/lto/pr61278_0.c: New test.
>>         * gcc.dg/lto/pr61278_1.c: New test.
>>
>> diff --git a/gcc/shrink-wrap.c b/gcc/shrink-wrap.c
>> index f09cfe7..be17829 100644
>> --- a/gcc/shrink-wrap.c
>> +++ b/gcc/shrink-wrap.c
>> @@ -204,8 +204,15 @@ move_insn_for_shrink_wrap (basic_block bb, rtx insn,
>>    /* Create a new basic block on the edge.  */
>>    if (EDGE_COUNT (next_block->preds) == 2)
>>      {
>> +      /* If DF_LIVE doesn't exist, i.e. at -O1, just give up.  */
>> +      if (!df_live)
>> +       return false;
>> +
>>        next_block = split_edge (live_edge);
>>
>> +      /* We create a new basic block.  Call df_grow_bb_info to make sure
>> +        all data structures are allocated.  */
>> +      df_grow_bb_info (df_live);
>>        bitmap_copy (df_get_live_in (next_block), df_get_live_out (bb));
>>        df_set_bb_dirty (next_block);
>>
>> diff --git a/gcc/testsuite/gcc.dg/lto/pr61278_0.c
>> b/gcc/testsuite/gcc.dg/lto/pr61278_0.c
>> new file mode 100644
>> index 0000000..03a24ae
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/lto/pr61278_0.c
>> @@ -0,0 +1,30 @@
>> +/* { dg-lto-do link } */
>> +/* { dg-lto-options { { -flto -O0 } } } */
>> +/* { dg-extra-ld-options " -flto -O1 " } */
>> +
>> +static unsigned int
>> +fn1 (int p1, int p2)
>> +{
>> +  return 0;
>> +}
>> +
>> +char a, b, c;
>> +
>> +char
>> +foo (char *p)
>> +{
>> +  int i;
>> +  for (b = 1 ; b > 0; b++)
>> +    {
>> +      for (i = 0; i < 2; i++)
>> +       ;
>> +      for (a = 1; a > 0; a++)
>> +       {
>> +         char d[1] = { 0 };
>> +         if (*p)
>> +           break;
>> +         c ^= fn1 (fn1 (fn1 (0, 0), 0), 0);
>> +       }
>> +    }
>> +  return 0;
>> +}
>> diff --git a/gcc/testsuite/gcc.dg/lto/pr61278_1.c
>> b/gcc/testsuite/gcc.dg/lto/pr61278_1.c
>> new file mode 100644
>> index 0000000..b02c8ac
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/lto/pr61278_1.c
>> @@ -0,0 +1,13 @@
>> +/* { dg-lto-do link } */
>> +/* { dg-lto-options { { -flto -O1 } } } */
>> +
>> +extern char foo (char *);
>> +
>> +char d;
>> +
>> +int
>> +main ()
>> +{
>> +  foo (&d);
>> +  return 0;
>> +}


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