[LLVMdev] fptoui calling a function that modifies ECX

Craig Topper craig.topper at gmail.com
Fri Jul 19 12:30:30 PDT 2013


Here's my attempt at a fix. Adding Jakob to make sure I did this right.


On Fri, Jul 19, 2013 at 2:34 AM, Peter Newman <peter at uformia.com> wrote:

>  That does appear to have worked. All my tests are passing now.
>
> I'll hand this out to our other devs & testers and make sure it's working
> for them as well (not just on my machine).
>
> Thank you, again.
>
> --
> Peter N
>
>
> On 19/07/2013 5:45 PM, Craig Topper wrote:
>
> I don't think that's going to work.
>
>
> On Fri, Jul 19, 2013 at 12:24 AM, Peter Newman <peter at uformia.com> wrote:
>
>>  Thank you, I'm trying this now.
>>
>>
>> On 19/07/2013 5:23 PM, Craig Topper wrote:
>>
>> Try adding ECX to the Defs of this part of
>> lib/Target/X86/X86InstrCompiler.td like I've done below. I don't have a
>> Windows machine to test myself.
>>
>>  let Defs = [EAX, EDX, ECX, EFLAGS], FPForm = SpecialFP in {
>>   def WIN_FTOL_32 : I<0, Pseudo, (outs), (ins RFP32:$src),
>>                       "# win32 fptoui",
>>                       [(X86WinFTOL RFP32:$src)]>,
>>                     Requires<[In32BitMode]>;
>>
>>    def WIN_FTOL_64 : I<0, Pseudo, (outs), (ins RFP64:$src),
>>                       "# win32 fptoui",
>>                       [(X86WinFTOL RFP64:$src)]>,
>>                     Requires<[In32BitMode]>;
>> }
>>
>>
>> On Thu, Jul 18, 2013 at 11:59 PM, Peter Newman <peter at uformia.com> wrote:
>>
>>>  Oh, excellent point, I agree. My bad. Now that I'm not assuming those
>>> are the sqrt, I see the sqrtpd's in the output. Also there are three
>>> fptoui's and there are 3 call instances.
>>>
>>> (Changing subject line again.)
>>>
>>> Now it looks like it's bug #13862
>>>
>>> On 19/07/2013 4:51 PM, Craig Topper wrote:
>>>
>>> I think those calls correspond to this
>>>
>>>    %110 = fptoui double %109 to i32
>>>
>>>  The calls are followed by an imul with 12 which matches up with what
>>> occurs right after the fptoui in the IR.
>>>
>>>
>>> On Thu, Jul 18, 2013 at 11:48 PM, Peter Newman <peter at uformia.com>wrote:
>>>
>>>>  Yes, that is the result of module-dump.ll
>>>>
>>>>
>>>> On 19/07/2013 4:46 PM, Craig Topper wrote:
>>>>
>>>> Does this correspond to one of the .ll files you sent earlier?
>>>>
>>>>
>>>> On Thu, Jul 18, 2013 at 11:34 PM, Peter Newman <peter at uformia.com>wrote:
>>>>
>>>>>  (Changing subject line as diagnosis has changed)
>>>>>
>>>>> I'm attaching the compiled code that I've been getting, both with
>>>>> CodeGenOpt::Default and CodeGenOpt::None . The crash isn't occurring with
>>>>> CodeGenOpt::None, but that seems to be because ECX isn't being used - it
>>>>> still gets set to 0x7fffffff by one of the calls to 76719BA1
>>>>>
>>>>> I notice that X86::SQRTPD[m|r] appear in
>>>>> X86InstrInfo::isHighLatencyDef. I was thinking an optimization might be
>>>>> removing it, but I don't get the sqrtpd instruction even if the createJIT
>>>>> optimization level turned off.
>>>>>
>>>>> I am trying this with the Release 3.3 code - I'll try it with trunk
>>>>> and see if I get a different result there. Maybe there was a recent commit
>>>>> for this.
>>>>>
>>>>> --
>>>>> Peter N
>>>>>
>>>>> On 19/07/2013 4:00 PM, Craig Topper wrote:
>>>>>
>>>>> Hmm, I'm not able to get those .ll files to compile if I disable SSE
>>>>> and I end up with SSE instructions(including sqrtpd) if I don't disable it.
>>>>>
>>>>>
>>>>>  On Thu, Jul 18, 2013 at 10:53 PM, Peter Newman <peter at uformia.com>wrote:
>>>>>
>>>>>>  Is there something specifically required to enable SSE? If it's not
>>>>>> detected as available (based from the target triple?) then I don't think we
>>>>>> enable it specifically.
>>>>>>
>>>>>> Also it seems that it should handle converting to/from the vector
>>>>>> types, although I can see it getting confused about needing to do that if
>>>>>> it thinks SSE isn't available at all.
>>>>>>
>>>>>>
>>>>>> On 19/07/2013 3:47 PM, Craig Topper wrote:
>>>>>>
>>>>>> Hmm, maybe sse isn't being enabled so its falling back to emulating
>>>>>> sqrt?
>>>>>>
>>>>>>
>>>>>> On Thu, Jul 18, 2013 at 10:45 PM, Peter Newman <peter at uformia.com>wrote:
>>>>>>
>>>>>>>  In the disassembly, I'm seeing three cases of
>>>>>>> call        76719BA1
>>>>>>>
>>>>>>> I am assuming this is the sqrt function as this is the only function
>>>>>>> called in the LLVM IR.
>>>>>>>
>>>>>>> The code at 76719BA1 is:
>>>>>>>
>>>>>>> 76719BA1  push        ebp
>>>>>>> 76719BA2  mov         ebp,esp
>>>>>>> 76719BA4  sub         esp,20h
>>>>>>> 76719BA7  and         esp,0FFFFFFF0h
>>>>>>> 76719BAA  fld         st(0)
>>>>>>> 76719BAC  fst         dword ptr [esp+18h]
>>>>>>> 76719BB0  fistp       qword ptr [esp+10h]
>>>>>>> 76719BB4  fild        qword ptr [esp+10h]
>>>>>>> 76719BB8  mov         edx,dword ptr [esp+18h]
>>>>>>> 76719BBC  mov         eax,dword ptr [esp+10h]
>>>>>>> 76719BC0  test        eax,eax
>>>>>>> 76719BC2  je          76719DCF
>>>>>>> 76719BC8  fsubp       st(1),st
>>>>>>> 76719BCA  test        edx,edx
>>>>>>> 76719BCC  js          7671F9DB
>>>>>>> 76719BD2  fstp        dword ptr [esp]
>>>>>>> 76719BD5  mov         ecx,dword ptr [esp]
>>>>>>> 76719BD8  add         ecx,7FFFFFFFh
>>>>>>> 76719BDE  sbb         eax,0
>>>>>>> 76719BE1  mov         edx,dword ptr [esp+14h]
>>>>>>> 76719BE5  sbb         edx,0
>>>>>>> 76719BE8  leave
>>>>>>> 76719BE9  ret
>>>>>>>
>>>>>>>
>>>>>>> As you can see at 76719BD5, it modifies ECX .
>>>>>>>
>>>>>>> I don't know that this is the sqrtpd function (for example, I'm not
>>>>>>> seeing any SSE instructions here?) but whatever it is, it's being called
>>>>>>> from the IR I attached earlier, and is modifying ECX under some
>>>>>>> circumstances.
>>>>>>>
>>>>>>>
>>>>>>> On 19/07/2013 3:29 PM, Craig Topper wrote:
>>>>>>>
>>>>>>> That should map directly to sqrtpd which can't modify ecx.
>>>>>>>
>>>>>>>
>>>>>>> On Thu, Jul 18, 2013 at 10:27 PM, Peter Newman <peter at uformia.com>wrote:
>>>>>>>
>>>>>>>>  Sorry, that should have been llvm.x86.sse2.sqrt.pd
>>>>>>>>
>>>>>>>>
>>>>>>>> On 19/07/2013 3:25 PM, Craig Topper wrote:
>>>>>>>>
>>>>>>>> What is "frep.x86.sse2.sqrt.pd". I'm only familiar with things
>>>>>>>> prefixed with "llvm.x86".
>>>>>>>>
>>>>>>>>
>>>>>>>> On Thu, Jul 18, 2013 at 10:12 PM, Peter Newman <peter at uformia.com>wrote:
>>>>>>>>
>>>>>>>>>  After stepping through the produced assembly, I believe I have a
>>>>>>>>> culprit.
>>>>>>>>>
>>>>>>>>> One of the calls to @frep.x86.sse2.sqrt.pd is modifying the value
>>>>>>>>> of ECX - while the produced code is expecting it to still contain its
>>>>>>>>> previous value.
>>>>>>>>>
>>>>>>>>> Peter N
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 19/07/2013 2:09 PM, Peter Newman wrote:
>>>>>>>>>
>>>>>>>>> I've attached the module->dump() that our code is producing.
>>>>>>>>> Unfortunately this is the smallest test case I have available.
>>>>>>>>>
>>>>>>>>> This is before any optimization passes are applied. There are two
>>>>>>>>> separate modules in existence at the time, and there are no guarantees
>>>>>>>>> about the order the surrounding code calls those functions, so there may be
>>>>>>>>> some interaction between them? There shouldn't be, they don't refer to any
>>>>>>>>> common memory etc. There is no multi-threading occurring.
>>>>>>>>>
>>>>>>>>> The function in module-dump.ll (called crashfunc in this file) is
>>>>>>>>> called with
>>>>>>>>> -        func_params    0x0018f3b0    double [3]
>>>>>>>>>         [0x0]    -11.339976634695301    double
>>>>>>>>>         [0x1]    -9.7504239056205506    double
>>>>>>>>>         [0x2]    -5.2900856817382804    double
>>>>>>>>> at the time of the exception.
>>>>>>>>>
>>>>>>>>> This is compiled on a "i686-pc-win32" triple. All of the
>>>>>>>>> non-intrinsic functions referred to in these modules are the standard
>>>>>>>>> equivalents from the MSVC library (e.g. @asin is the standard C lib
>>>>>>>>> double asin( double ) ).
>>>>>>>>>
>>>>>>>>> Hopefully this is reproducible for you.
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> PeterN
>>>>>>>>>
>>>>>>>>> On 18/07/2013 4:37 PM, Craig Topper wrote:
>>>>>>>>>
>>>>>>>>> Are you able to send any IR for others to reproduce this issue?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Wed, Jul 17, 2013 at 11:23 PM, Peter Newman <peter at uformia.com>wrote:
>>>>>>>>>
>>>>>>>>>> Unfortunately, this doesn't appear to be the bug I'm hitting. I
>>>>>>>>>> applied the fix to my source and it didn't make a difference.
>>>>>>>>>>
>>>>>>>>>> Also further testing found me getting the same behavior with
>>>>>>>>>> other SIMD instructions. The common factor is in each case, ECX is set to
>>>>>>>>>> 0x7fffffff, and it's an operation using xmm ptr ecx+offset .
>>>>>>>>>>
>>>>>>>>>> Additionally, turning the optimization level passed to createJIT
>>>>>>>>>> down appears to avoid it, so I'm now leaning towards a bug in one of the
>>>>>>>>>> optimization passes.
>>>>>>>>>>
>>>>>>>>>> I'm going to dig through the passes controlled by that parameter
>>>>>>>>>> and see if I can narrow down which optimization is causing it.
>>>>>>>>>>
>>>>>>>>>> Peter N
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On 17/07/2013 1:58 PM, Solomon Boulos wrote:
>>>>>>>>>>
>>>>>>>>>>> As someone off list just told me, perhaps my new bug is the same
>>>>>>>>>>> issue:
>>>>>>>>>>>
>>>>>>>>>>>    http://llvm.org/bugs/show_bug.cgi?id=16640
>>>>>>>>>>>
>>>>>>>>>>> Do you happen to be using FastISel?
>>>>>>>>>>>
>>>>>>>>>>> Solomon
>>>>>>>>>>>
>>>>>>>>>>> On Jul 16, 2013, at 6:39 PM, Peter Newman <peter at uformia.com>
>>>>>>>>>>> wrote:
>>>>>>>>>>>
>>>>>>>>>>>  Hello all,
>>>>>>>>>>>>
>>>>>>>>>>>> I'm currently in the process of debugging a crash occurring in
>>>>>>>>>>>> our program. In LLVM 3.2 and 3.3 it appears that JIT generated code is
>>>>>>>>>>>> attempting to perform access unaligned memory with a SSE2 instruction.
>>>>>>>>>>>> However this only happens under certain conditions that seem (but may not
>>>>>>>>>>>> be) related to the stacks state on calling the function.
>>>>>>>>>>>>
>>>>>>>>>>>> Our program acts as a front-end, using the LLVM C++ API to
>>>>>>>>>>>> generate a JIT generated function. This function is primarily mathematical,
>>>>>>>>>>>> so we use the Vector types to take advantage of SIMD instructions (as well
>>>>>>>>>>>> as a few SSE2 intrinsics).
>>>>>>>>>>>>
>>>>>>>>>>>> This worked in LLVM 2.8 but started failing in 3.2 and has
>>>>>>>>>>>> continued to fail in 3.3. It fails with no optimizations applied to the
>>>>>>>>>>>> LLVM Function/Module. It crashes with what is reported as a memory access
>>>>>>>>>>>> error (accessing 0xffffffff), however it's suggested that this is how the
>>>>>>>>>>>> SSE fault raising mechanism appears.
>>>>>>>>>>>>
>>>>>>>>>>>> The generated instruction varies, but it seems to often be
>>>>>>>>>>>> similar to (I don't have it in front of me, sorry):
>>>>>>>>>>>> movapd xmm0, xmm[ecx+0x???????]
>>>>>>>>>>>> Where the xmm register changes, and the second parameter is a
>>>>>>>>>>>> memory access.
>>>>>>>>>>>> ECX is always set to 0x7ffffff - however I don't know if this
>>>>>>>>>>>> is part of the SSE error reporting process or is part of the situation
>>>>>>>>>>>> causing the error.
>>>>>>>>>>>>
>>>>>>>>>>>> I haven't worked out exactly what code path etc is causing this
>>>>>>>>>>>> crash. I'm hoping that someone can tell me if there were any changed
>>>>>>>>>>>> requirements for working with SIMD in LLVM 3.2 (or earlier, we haven't
>>>>>>>>>>>> tried 3.0 or 3.1). I currently suspect the use of GlobalVariable (we first
>>>>>>>>>>>> discovered the crash when using a feature that uses them), however I have
>>>>>>>>>>>> attempted using setAlignment on the GlobalVariables without any change.
>>>>>>>>>>>>
>>>>>>>>>>>> --
>>>>>>>>>>>> Peter N
>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>> LLVM Developers mailing list
>>>>>>>>>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>>>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>> _______________________________________________
>>>>>>>>>> LLVM Developers mailing list
>>>>>>>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>  --
>>>>>>>>> ~Craig
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>  --
>>>>>>>> ~Craig
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>  --
>>>>>>> ~Craig
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>>  --
>>>>>> ~Craig
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>>  --
>>>>> ~Craig
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>>  --
>>>> ~Craig
>>>>
>>>>
>>>>
>>>
>>>
>>>  --
>>> ~Craig
>>>
>>>
>>>
>>
>>
>>  --
>> ~Craig
>>
>>
>>
>
>
>  --
> ~Craig
>
>
>


-- 
~Craig
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