Craig Topper
2013-Jul-19 05:25 UTC
[LLVMdev] SIMD instructions and memory alignment on X86
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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130718/21541c86/attachment.html>
Peter Newman
2013-Jul-19 05:27 UTC
[LLVMdev] SIMD instructions and memory alignment on X86
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 > <mailto: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 <mailto: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 <mailto: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 <mailto: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 <mailto:LLVMdev at cs.uiuc.edu> >>> http://llvm.cs.uiuc.edu >>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >>> >>> >>> >>> >>> -- >>> ~Craig >> > > > > > -- > ~Craig-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130719/b682ab33/attachment.html>
Craig Topper
2013-Jul-19 05:29 UTC
[LLVMdev] SIMD instructions and memory alignment on X86
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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130718/b1fdb808/attachment.html>
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