llvm dev - Jul 2016 - Hitting assertion failure related to vectorization + instcombine

Thanks for notifying me. Yes, this was a recent change. Taking a look now.

On Wed, Jul 20, 2016 at 1:49 PM, Michael Kuperstein <mkuper at google.com>
wrote:
> +Sanjay, who touched this last. :-)
>
> On Wed, Jul 20, 2016 at 12:44 PM, Ismail Badawi (ibadawi) via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi folks,
>>
>> I'm hitting the below assertion failure when compiling this small
piece
>> of C code (repro.c, attached).
>>
>> My command line is:
>>
>> bin/clang --target=aarch64-linux-gnu -c -O2 repro.c
>>
>> clang is built from top of trunk as of this morning. It only happens at
>> -O2, and it doesn't happen with the default target (x86_64). I
tried to
>> reproduce using just 'llc -O2' but didn't manage -- but I
do have this
>> reduced opt command line (repro.ll also attached, just generated from
>> repro.c at -O0):
>>
>> bin/opt -instcombine -licm -simplifycfg -instcombine -loop-rotate
>> -loop-vectorize -instcombine < repro.ll
>>
>> The failure is:
>>
>> opt: /scratch/1/ismail/llvm-upstream/include/llvm/ADT/APInt.h:983: bool
>> llvm::APInt::operator==(const llvm::APInt&) const: Assertion
`BitWidth =>> RHS.BitWidth && "Comparison requires equal bit
widths"' failed.
>> ...snip...
>> #8 0x00000000013a8553 llvm::APInt::operator==(llvm::APInt const&)
const
>> /scratch/1/ismail/llvm-upstream/include/llvm/ADT/APInt.h:984:0
>> #9 0x0000000001f875b0 simplifySelectBitTest(llvm::Value*, llvm::Value*,
>> llvm::Value*, llvm::APInt const*, bool)
>>
/scratch/1/ismail/llvm-upstream/lib/Analysis/InstructionSimplify.cpp:3388:0
>> #10 0x0000000001f87ad5 simplifySelectWithICmpCond(llvm::Value*,
>> llvm::Value*, llvm::Value*, (anonymous namespace)::Query const&,
unsigned
>> int)
>>
/scratch/1/ismail/llvm-upstream/lib/Analysis/InstructionSimplify.cpp:3434:0
>> #11 0x0000000001f87f6a SimplifySelectInst(llvm::Value*, llvm::Value*,
>> llvm::Value*, (anonymous namespace)::Query const&, unsigned int)
>>
/scratch/1/ismail/llvm-upstream/lib/Analysis/InstructionSimplify.cpp:3515:0
>> #12 0x0000000001f87fe3 llvm::SimplifySelectInst(llvm::Value*,
>> llvm::Value*, llvm::Value*, llvm::DataLayout const&,
>> llvm::TargetLibraryInfo const*, llvm::DominatorTree const*,
>> llvm::AssumptionCache*, llvm::Instruction const*)
>>
/scratch/1/ismail/llvm-upstream/lib/Analysis/InstructionSimplify.cpp:3528:0
>> ...snip...
>> Stack dump:
>> 0.  Program arguments: debugbuild/bin/opt -instcombine -licm
-simplifycfg
>> -instcombine -loop-rotate -loop-vectorize -instcombine
>> 1.  Running pass 'Function Pass Manager' on module
'<stdin>'.
>> 2.  Running pass 'Combine redundant instructions' on function
'@strsave'
>>
>> ---
>>
>> Looking at the code, the issue is with this line:
>>
>>   if (TrueVal == X && match(FalseVal, m_And(m_Specific(X),
m_APInt(C))) &&
>>         *Y == ~*C)
>>
>> In this case Y is a 128-bit APInt, and so is the value that C is
>> extracted from, but the m_APInt matcher has code that calls
getSplatValue()
>> if the matched expression has vector type. So C ends up as an 8-bit
value,
>> triggering the assertion failure on the call to ==.
>>
>> The issue is clear but I'm not sure what the correct fix should be
--
>> whether this code is just not meant to work with vector types, or
whether
>> the call to getSplatValue() doesn't belong in the matcher, or
whether there
>> should be a corresponding call to getSplatValue() on the caller side,
or
>> something else.
>>
>> Any help from someone with more context would be appreciated.
>>
>> Thanks,
>> Ismail
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
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Quick update - the bug existed before I refactored that chunk in
InstSimplify with:
https://reviews.llvm.org/rL275911

In fact, as discussed in https://reviews.llvm.org/D22537 - because we have
a big pile of lazily copied code, the bug has an identical twin that exists
in InstCombine. I swear I didn't touch that code...yet. :)

define <2 x i32> @select_icmp_vec(<2 x i32> %x) {
  %cmp = icmp slt <2 x i32> %x, zeroinitializer
  %xor = xor <2 x i32> %x, <i32 2147483648, i32 2147483648>
  %x.xor = select <2 x i1> %cmp, <2 x i32> %x, <2 x i32> %xor
  ret <2 x i32> %x.xor
}

$ ./opt -instcombine selvec.ll -S
Assertion failed: (BitWidth == RHS.BitWidth && "Comparison requires
equal
bit widths"), function operator==, file
/Users/spatel/myllvm/llvm/include/llvm/ADT/APInt.h, line 983.

I should have a patch up for review shortly.


On Wed, Jul 20, 2016 at 2:03 PM, Sanjay Patel <spatel at rotateright.com>
wrote:
> Thanks for notifying me. Yes, this was a recent change. Taking a look now.
>
> On Wed, Jul 20, 2016 at 1:49 PM, Michael Kuperstein <mkuper at
google.com>
> wrote:
>
>> +Sanjay, who touched this last. :-)
>>
>> On Wed, Jul 20, 2016 at 12:44 PM, Ismail Badawi (ibadawi) via llvm-dev
<
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> Hi folks,
>>>
>>> I'm hitting the below assertion failure when compiling this
small piece
>>> of C code (repro.c, attached).
>>>
>>> My command line is:
>>>
>>> bin/clang --target=aarch64-linux-gnu -c -O2 repro.c
>>>
>>> clang is built from top of trunk as of this morning. It only
happens at
>>> -O2, and it doesn't happen with the default target (x86_64). I
tried to
>>> reproduce using just 'llc -O2' but didn't manage -- but
I do have this
>>> reduced opt command line (repro.ll also attached, just generated
from
>>> repro.c at -O0):
>>>
>>> bin/opt -instcombine -licm -simplifycfg -instcombine -loop-rotate
>>> -loop-vectorize -instcombine < repro.ll
>>>
>>> The failure is:
>>>
>>> opt: /scratch/1/ismail/llvm-upstream/include/llvm/ADT/APInt.h:983:
bool
>>> llvm::APInt::operator==(const llvm::APInt&) const: Assertion
`BitWidth =>>> RHS.BitWidth && "Comparison requires equal
bit widths"' failed.
>>> ...snip...
>>> #8 0x00000000013a8553 llvm::APInt::operator==(llvm::APInt
const&) const
>>> /scratch/1/ismail/llvm-upstream/include/llvm/ADT/APInt.h:984:0
>>> #9 0x0000000001f875b0 simplifySelectBitTest(llvm::Value*,
llvm::Value*,
>>> llvm::Value*, llvm::APInt const*, bool)
>>>
/scratch/1/ismail/llvm-upstream/lib/Analysis/InstructionSimplify.cpp:3388:0
>>> #10 0x0000000001f87ad5 simplifySelectWithICmpCond(llvm::Value*,
>>> llvm::Value*, llvm::Value*, (anonymous namespace)::Query
const&, unsigned
>>> int)
>>>
/scratch/1/ismail/llvm-upstream/lib/Analysis/InstructionSimplify.cpp:3434:0
>>> #11 0x0000000001f87f6a SimplifySelectInst(llvm::Value*,
llvm::Value*,
>>> llvm::Value*, (anonymous namespace)::Query const&, unsigned
int)
>>>
/scratch/1/ismail/llvm-upstream/lib/Analysis/InstructionSimplify.cpp:3515:0
>>> #12 0x0000000001f87fe3 llvm::SimplifySelectInst(llvm::Value*,
>>> llvm::Value*, llvm::Value*, llvm::DataLayout const&,
>>> llvm::TargetLibraryInfo const*, llvm::DominatorTree const*,
>>> llvm::AssumptionCache*, llvm::Instruction const*)
>>>
/scratch/1/ismail/llvm-upstream/lib/Analysis/InstructionSimplify.cpp:3528:0
>>> ...snip...
>>> Stack dump:
>>> 0.  Program arguments: debugbuild/bin/opt -instcombine -licm
>>> -simplifycfg -instcombine -loop-rotate -loop-vectorize -instcombine
>>> 1.  Running pass 'Function Pass Manager' on module
'<stdin>'.
>>> 2.  Running pass 'Combine redundant instructions' on
function '@strsave'
>>>
>>> ---
>>>
>>> Looking at the code, the issue is with this line:
>>>
>>>   if (TrueVal == X && match(FalseVal, m_And(m_Specific(X),
m_APInt(C)))
>>> &&
>>>         *Y == ~*C)
>>>
>>> In this case Y is a 128-bit APInt, and so is the value that C is
>>> extracted from, but the m_APInt matcher has code that calls
getSplatValue()
>>> if the matched expression has vector type. So C ends up as an 8-bit
value,
>>> triggering the assertion failure on the call to ==.
>>>
>>> The issue is clear but I'm not sure what the correct fix should
be --
>>> whether this code is just not meant to work with vector types, or
whether
>>> the call to getSplatValue() doesn't belong in the matcher, or
whether there
>>> should be a corresponding call to getSplatValue() on the caller
side, or
>>> something else.
>>>
>>> Any help from someone with more context would be appreciated.
>>>
>>> Thanks,
>>> Ismail
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
>>
>
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Sanjay: let me know if this is something that will apply to 3.9.

Thanks,
Hans

On Wed, Jul 20, 2016 at 5:59 PM, Sanjay Patel via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Quick update - the bug existed before I refactored that chunk in
> InstSimplify with:
> https://reviews.llvm.org/rL275911
>
> In fact, as discussed in https://reviews.llvm.org/D22537 - because we have
a
> big pile of lazily copied code, the bug has an identical twin that exists
in
> InstCombine. I swear I didn't touch that code...yet. :)
>
> define <2 x i32> @select_icmp_vec(<2 x i32> %x) {
>   %cmp = icmp slt <2 x i32> %x, zeroinitializer
>   %xor = xor <2 x i32> %x, <i32 2147483648, i32 2147483648>
>   %x.xor = select <2 x i1> %cmp, <2 x i32> %x, <2 x i32>
%xor
>   ret <2 x i32> %x.xor
> }
>
> $ ./opt -instcombine selvec.ll -S
> Assertion failed: (BitWidth == RHS.BitWidth && "Comparison
requires equal
> bit widths"), function operator==, file
> /Users/spatel/myllvm/llvm/include/llvm/ADT/APInt.h, line 983.
>
> I should have a patch up for review shortly.
>
>
> On Wed, Jul 20, 2016 at 2:03 PM, Sanjay Patel <spatel at
rotateright.com>
> wrote:
>>
>> Thanks for notifying me. Yes, this was a recent change. Taking a look
now.
>>
>> On Wed, Jul 20, 2016 at 1:49 PM, Michael Kuperstein <mkuper at
google.com>
>> wrote:
>>>
>>> +Sanjay, who touched this last. :-)
>>>
>>> On Wed, Jul 20, 2016 at 12:44 PM, Ismail Badawi (ibadawi) via
llvm-dev
>>> <llvm-dev at lists.llvm.org> wrote:
>>>>
>>>> Hi folks,
>>>>
>>>> I'm hitting the below assertion failure when compiling this
small piece
>>>> of C code (repro.c, attached).
>>>>
>>>> My command line is:
>>>>
>>>> bin/clang --target=aarch64-linux-gnu -c -O2 repro.c
>>>>
>>>> clang is built from top of trunk as of this morning. It only
happens at
>>>> -O2, and it doesn't happen with the default target
(x86_64). I tried to
>>>> reproduce using just 'llc -O2' but didn't manage --
but I do have this
>>>> reduced opt command line (repro.ll also attached, just
generated from
>>>> repro.c at -O0):
>>>>
>>>> bin/opt -instcombine -licm -simplifycfg -instcombine
-loop-rotate
>>>> -loop-vectorize -instcombine < repro.ll
>>>>
>>>> The failure is:
>>>>
>>>> opt:
/scratch/1/ismail/llvm-upstream/include/llvm/ADT/APInt.h:983: bool
>>>> llvm::APInt::operator==(const llvm::APInt&) const:
Assertion `BitWidth =>>>> RHS.BitWidth && "Comparison
requires equal bit widths"' failed.
>>>> ...snip...
>>>> #8 0x00000000013a8553 llvm::APInt::operator==(llvm::APInt
const&) const
>>>> /scratch/1/ismail/llvm-upstream/include/llvm/ADT/APInt.h:984:0
>>>> #9 0x0000000001f875b0 simplifySelectBitTest(llvm::Value*,
llvm::Value*,
>>>> llvm::Value*, llvm::APInt const*, bool)
>>>>
/scratch/1/ismail/llvm-upstream/lib/Analysis/InstructionSimplify.cpp:3388:0
>>>> #10 0x0000000001f87ad5 simplifySelectWithICmpCond(llvm::Value*,
>>>> llvm::Value*, llvm::Value*, (anonymous namespace)::Query
const&, unsigned
>>>> int)
>>>>
/scratch/1/ismail/llvm-upstream/lib/Analysis/InstructionSimplify.cpp:3434:0
>>>> #11 0x0000000001f87f6a SimplifySelectInst(llvm::Value*,
llvm::Value*,
>>>> llvm::Value*, (anonymous namespace)::Query const&, unsigned
int)
>>>>
/scratch/1/ismail/llvm-upstream/lib/Analysis/InstructionSimplify.cpp:3515:0
>>>> #12 0x0000000001f87fe3 llvm::SimplifySelectInst(llvm::Value*,
>>>> llvm::Value*, llvm::Value*, llvm::DataLayout const&,
llvm::TargetLibraryInfo
>>>> const*, llvm::DominatorTree const*, llvm::AssumptionCache*,
>>>> llvm::Instruction const*)
>>>>
/scratch/1/ismail/llvm-upstream/lib/Analysis/InstructionSimplify.cpp:3528:0
>>>> ...snip...
>>>> Stack dump:
>>>> 0.  Program arguments: debugbuild/bin/opt -instcombine -licm
>>>> -simplifycfg -instcombine -loop-rotate -loop-vectorize
-instcombine
>>>> 1.  Running pass 'Function Pass Manager' on module
'<stdin>'.
>>>> 2.  Running pass 'Combine redundant instructions' on
function '@strsave'
>>>>
>>>> ---
>>>>
>>>> Looking at the code, the issue is with this line:
>>>>
>>>>   if (TrueVal == X && match(FalseVal,
m_And(m_Specific(X), m_APInt(C)))
>>>> &&
>>>>         *Y == ~*C)
>>>>
>>>> In this case Y is a 128-bit APInt, and so is the value that C
is
>>>> extracted from, but the m_APInt matcher has code that calls
getSplatValue()
>>>> if the matched expression has vector type. So C ends up as an
8-bit value,
>>>> triggering the assertion failure on the call to ==.
>>>>
>>>> The issue is clear but I'm not sure what the correct fix
should be --
>>>> whether this code is just not meant to work with vector types,
or whether
>>>> the call to getSplatValue() doesn't belong in the matcher,
or whether there
>>>> should be a corresponding call to getSplatValue() on the caller
side, or
>>>> something else.
>>>>
>>>> Any help from someone with more context would be appreciated.
>>>>
>>>> Thanks,
>>>> Ismail
>>>>
>>>>
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> llvm-dev at lists.llvm.org
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>>
>>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>