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Re: PATCH: Properly check the end of basic block
On Thu, Nov 18, 2010 at 12:36 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> @@ -118,9 +118,12 @@ move_or_delete_vzeroupper_2 (basic_block bb, bool
>> upper_128bits_set)
>> ? ? ? ? ? ? bb->index, upper_128bits_set);
>>
>> ? insn = BB_HEAD (bb);
>> + ?last = NEXT_INSN (BB_END (bb));
>> ? while (insn != BB_END (bb))
>> ? ? {
>> ? ? ? insn = NEXT_INSN (insn);
>> + ? ? ?if (insn == last)
>> + ? ? ? break;
>>
>> ? ? ? if (!NONDEBUG_INSN_P (insn))
>> ? ? ? ?continue;
>>
>> The change above is not needed. The new check is never triggered - the
>> loop terminates when "insn == BB_END (bb)" at "while", so I fail to
>> see why additional termination for "NEXT_INSN (insn) == NEXT_INSN
>> (BB_END (bb))" is needed.
>
> Here is the patch for
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46519
>
> We have 2 blocks pointing to each others. This patch first scans
> all blocks without moving vzeroupper so that we can have accurate
> information about upper 128bits at block entry.
>
>> (The BB_HEAD (bb) is either a NOTE or CODE_LABEL so it can be skipped
>> with NEXT_INSN.)
>
> Please try gcc.target/i386/avx-vzeroupper-20.c. ?It will
> trigger this condition.
It doesn't even trigger move_or_delete_vzeroupper.
OK, I have hacked gcc a bit to blindly trigger the function in order
to check the loop iself. For your testcase we process following insn
stream:
2 bb 2 [10000]
3 bb 3 [7836]
4 bb 4 [2164]
1 NOTE_INSN_DELETED
4 NOTE_INSN_BASIC_BLOCK
17 NOTE_INSN_PROLOGUE_END
3 NOTE_INSN_FUNCTION_BEG
6 flags:CCZ=cmp(di:DI,0)
7 pc={(flags:CCZ==0)?L14:pc}
REG_DEAD: flags:CCZ
REG_BR_PROB: 0x874
8 NOTE_INSN_BASIC_BLOCK
20 NOTE_INSN_EPILOGUE_BEG
10 call <...>
REG_DEAD: di:DI
REG_EH_REGION: 0
i 11: barrier
L14:
15 NOTE_INSN_BASIC_BLOCK
19 return
i 18: barrier
16 NOTE_INSN_DELETED
And the loop processed:
Assembling functions:
bar
======
4 NOTE_INSN_BASIC_BLOCK
++++++++
6 flags:CCZ=cmp(di:DI,0)
++++++++
7 pc={(flags:CCZ==0)?L14:pc}
REG_DEAD: flags:CCZ
REG_BR_PROB: 0x874
======
8 NOTE_INSN_BASIC_BLOCK
++++++++
10 call <...>
REG_DEAD: di:DI
REG_EH_REGION: 0
======
L14:
++++++++
23 {return;unspec{0;};}
Where "===" precedes instruction, detected as BB_START and "+++"
precedes instructions that passed !NONDEBUG_INSN_P filter.
Please, can you show me the exact insn that was missed in this
particular testcase. I have used "-O3 -mavx -mtune=generic" and I have
to short-circuit the check for uses_vzeroupper_p at the end of
ix86_reorg.
Uros.