[shrink-wrap] should not sink instructions which may cause trap ?

[Jiong Wang]

2014-09-25 14:07 GMT+01:00 Jiong Wang <jiong.wang@arm.com>:
>
> On 25/09/14 12:25, Christophe Lyon wrote:
>>
>>>
>> I have observed regressions in the g++ testsuite: pr49847 now FAILs
>> after this patch.
>
> no.
>
> even without my patch, the regression still happen.
>
> or you could specify -fno-shrink-wrap, gcc still crash.
>
> so, this regression should caused by other commits which haven't exposed on
> x86 regression test.

sorry, confirmed, there is regression.

my code was git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@215590.
there also be gcc crash on aarch64, with the following info,
  pr49847.C:5:21: internal compiler error: Segmentation fault
     try { return g >= 0; }
                     ^
  0xdc249e crash_signal
      ../../gcc/gcc/toplev.c:340
  0xdbfeff default_get_reg_raw_mode(int)

so I was thinking it's caused by other commits instead of this, and after I sync
code to git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@215599 I could
reproduce this bug.

  error: missing REG_EH_REGION note at the end of bb 2

the reson is:
  * before this patch, we only sink simple "set reg, reg" instruction which
    the corresponding instruction will not produce exception, thus no
REG_EH_REGION attached.
  * after this patch, we will sink instruction like the following for
aarch64 or arm or other RISC.

    (insn 7 3 30 2 (set (reg:CCFPE 66 cc)
        (compare:CCFPE (reg:SF 32 v0 [ g ])
            (const_double:SF 0.0 [0x0.0p+0]))) pr49847.C:5 330 {*cmpesf}
     (expr_list:REG_DEAD (reg:SF 32 v0 [ g ])
        (expr_list:REG_EH_REGION (const_int 1 [0x1])
            (nil))))

  "compare" is actually a operator which may cause trap and we need to prevent
  any instruction which may causing trap be sink, because that may
break exception handling logic

  so something like the following should be added to the iterator check

  if (may_trap_p (x))
    don't sink this instruction.

   any comments?

   I will try to send a fix tomorrow.

   thanks.

-- Jiong


>
> -- Jiong
>
>
>>
>> Here is what I have in my logs:
>>
>> /aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-arm-none-linux-gnueabihf/gcc3/gcc/testsuite/g++/../../xg++
>>
>> -B/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-arm-none-linux-gnueabihf/gcc3/gcc/testsuite/g++/../../
>> /aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/testsuite/g++.dg/pr49847.C
>> -fno-diagnostics-show-caret -fdiagnostics-color=never  -nostdinc++
>>
>> -I/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-arm-none-linux-gnueabihf/gcc3/arm-none-linux-gnueabihf/libstdc++-v3/include/arm-none-linux-gnueabihf
>>
>> -I/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-arm-none-linux-gnueabihf/gcc3/arm-none-linux-gnueabihf/libstdc++-v3/include
>> -I/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libstdc++-v3/libsupc++
>> -I/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libstdc++-v3/include/backward
>> -I/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libstdc++-v3/testsuite/util
>> -fmessage-length=0  -std=gnu++98 -O -fnon-call-exceptions  -S     -o
>> pr49847.s    (timeout = 800)
>> /aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/testsuite/g++.dg/pr49847.C: In
>> function 'int f(float)':
>> /aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/testsuite/g++.dg/pr49847.C:7:1:
>> error: missing REG_EH_REGION note at the end of bb 2
>> /aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/testsuite/g++.dg/pr49847.C:7:1:
>> internal compiler error: verify_flow_info failed
>> 0x82f8ba verify_flow_info()
>>          /aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/cfghooks.c:260
>>
>> 0x840cd3 commit_edge_insertions()
>>          /aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/cfgrtl.c:2068
>> 0x9bf243 thread_prologue_and_epilogue_insns
>>          /aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/function.c:5852
>> 0x9bfa52 rest_of_handle_thread_prologue_and_epilogue
>>          /aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/function.c:6245
>> 0x9bfa52 execute
>>          /aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/function.c:6283
>>
>> As per
>>
>> http://cbuild.validation.linaro.org/build/cross-validation/gcc/trunk/215563/report-build-info.html
>> I've noticed this on targets:
>> arm-none-linux-gnueabihf
>> armeb-none-linux-gnueabihf
>> aarch64-none-elf
>> aarch64_be-none-elf
>> aarch64-none-linux-gnu
>> but NOT on
>> arm-none-eabi
>> arm-none-linux-gnueabi
>>
>> Christophe.
>>
>
>