[LLVMdev] Crash with optimization for size

[Bob Wilson]

This is  http://llvm.org/pr10514
Unfortunately the fix did not make it into that version of clang.

On Oct 20, 2011, at 7:47 AM, Somorjai, Akos wrote:

> Here's a code generated with -Os on darwin/x86_64 with clang from the Xcode 4.2 GM toolset on Mac OSX 10.7.2 (Apple clang version 3.0 (tags/Apple/clang-211.10.1) (based on LLVM 3.0svn), Target: x86_64-apple-darwin11.2.0)
> 
> 0x000000010277d281  <+2102>  lea    0x1d43bd0(%rip),%rax        # 0x1044c0e58 <gFloorPlanCutData>
> 0x000000010277d288  <+2109>  movaps 0x80(%rax),%xmm0
> 0x000000010277d28f  <+2116>  movaps %xmm0,-0x40(%rbp)
> 
> 
> The documentation for 'movaps' states: "When the source or destination operand is a memory location, it must be aligned on a 16-byte boundary." The problem is that the address of the global variable loaded into AX is not necessarily aligned; as it isn't in our case, which leads to the crash.
> 
> Here's is the code; it is loading the address of a global variable into AX, and tries to copy the data member, coming from the following class:
> 
> MD5::FingerPrint
> cutDataCheckSum = ::gFloorPlanCutData.GetCutDataCheckSum ();
> memcpy (elemData->cutDataCheckSum, cutDataCheckSum.data, sizeof (elemData->cutDataCheckSum));
> 
> 
> namespace MD5 {
> class GSROOT_DLL_EXPORT FingerPrint {
> public:
> FingerPrint ();
> virtual ~FingerPrint () {};
> FingerPrint (unsigned char fp[16]);
> 
> void                Set (unsigned char fp[16]);
> virtual
> GSErrCode Write (GS::OChannel& oc) const;
> virtual
> GSErrCode Read (GS::IChannel& ic);
> virtual
> GSErrCode GetAsString (char* md5String) const;
> bool
> IsEmpty (void) const;
> void
> Clear (void);
> bool                operator == (const FingerPrint&
> rhs) const;
> bool                operator != (const FingerPrint&
> rhs) const;
> FingerPrint&
> operator= (const FingerPrint& source);
> public:
> unsigned char       data[16];
> };
> }
> 
> The type of gFloorPlanCutData is
> 
> class   FloorPlanCutData: public GS::Object,
>   public GS::StateEventSource {
> 
> DECLARE_CLASS_INFO
> 
> private:
> double  currCutLevel;
> double  topCutLevel;
> double  bottomCutLevel;
> short   topCutBaseStoryRelativeIndex;
> short   bottomCutBaseStoryRelativeIndex;
> 
> double  fixLevel2Absolute0;
> 
> Int32
> lock;
> 
> // temporary data dependent from the current story
> double
> currCutLevelCalculated;
> double
> topCutLevelCalculated;
> double  currentStoryLevel;
> double  topBase2Current;
> double  bottomBase2Current;
> short   currentFloorIndex;
> bool
> relativeCalculated;
> MD5::FingerPrint
> cutDataCheckSum;
> 
> ...
> }
> 
> The optimization kicks in because 'data' is 16-bytes; but there's no alignment check…
> 
> This seems to be a code generation error, but I couldn't reproduce it in a small application. Is this a known bug, or shall I adjust my build settings?
> 
> Thanks,
> 
> Ákos Somorjai
> Developer Support Manager
> 
> GRAPHISOFT | Graphisoft Park 1. Budapest 1031 Hungary | +36 1 437-3000 | asomorjai at graphisoft.com
> 
> 
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