[llvm] r176407 - add getUnderlyingObjectSize()
Shuxin Yang
shuxin.llvm at gmail.com
Sat Mar 2 14:05:35 PST 2013
I don't like this change. That was exactly my original proposed solution
for the 14988. At the time I propose this
proposal. I didn't know there is a function called
'isIdentfiedObject()". Arnold told me that offline. After I discuss
with Arnold. I think his solution is better -- just give up if the
pointer is not pointing to the object, and it is up to
the getUnderlyingObject to points to the base address of the object.
getUnderlyingObject() certainly needs some enhancement in order to
handle phi node.
It think it is better to keep my comment to the pretty confusing term
"object". I don't think 99% people hanging out here
can clearly understand the subtle difference in the different context.
On 03/02/2013 08:27 AM, Arnold wrote:
> Nice, thanks.
>
>
> Sent from my iPhone
>
> On Mar 2, 2013, at 5:23 AM, Nuno Lopes <nunoplopes at sapo.pt> wrote:
>
>> Author: nlopes
>> Date: Sat Mar 2 05:23:34 2013
>> New Revision: 176407
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=176407&view=rev
>> Log:
>> add getUnderlyingObjectSize()
>> this is similar to getObjectSize(), but doesnt subtract the offset
>> tweak the BasicAA code accordingly (per PR14988)
>>
>> Modified:
>> llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h
>> llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
>> llvm/trunk/lib/Analysis/MemoryBuiltins.cpp
>>
>> Modified: llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h?rev=176407&r1=176406&r2=176407&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h (original)
>> +++ llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h Sat Mar 2 05:23:34 2013
>> @@ -144,6 +144,14 @@ static inline CallInst *isFreeCall(Value
>> bool getObjectSize(const Value *Ptr, uint64_t &Size, const DataLayout *TD,
>> const TargetLibraryInfo *TLI, bool RoundToAlign = false);
>>
>> +/// \brief Compute the size of the underlying object pointed by Ptr. Returns
>> +/// true and the object size in Size if successful, and false otherwise.
>> +/// If RoundToAlign is true, then Size is rounded up to the aligment of allocas,
>> +/// byval arguments, and global variables.
>> +bool getUnderlyingObjectSize(const Value *Ptr, uint64_t &Size,
>> + const DataLayout *TD, const TargetLibraryInfo *TLI,
>> + bool RoundToAlign = false);
>> +
>>
>>
>> typedef std::pair<APInt, APInt> SizeOffsetType;
>>
>> Modified: llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=176407&r1=176406&r2=176407&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
>> +++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Sat Mar 2 05:23:34 2013
>> @@ -88,7 +88,7 @@ static uint64_t getObjectSize(const Valu
>> const TargetLibraryInfo &TLI,
>> bool RoundToAlign = false) {
>> uint64_t Size;
>> - if (getObjectSize(V, Size, &TD, &TLI, RoundToAlign))
>> + if (getUnderlyingObjectSize(V, Size, &TD, &TLI, RoundToAlign))
>> return Size;
>> return AliasAnalysis::UnknownSize;
>> }
>> @@ -98,35 +98,6 @@ static uint64_t getObjectSize(const Valu
>> static bool isObjectSmallerThan(const Value *V, uint64_t Size,
>> const DataLayout &TD,
>> const TargetLibraryInfo &TLI) {
>> - // Note that the meanings of the "object" are slightly different in the
>> - // following contexts:
>> - // c1: llvm::getObjectSize()
>> - // c2: llvm.objectsize() intrinsic
>> - // c3: isObjectSmallerThan()
>> - // c1 and c2 share the same meaning; however, the meaning of "object" in c3
>> - // refers to the "entire object".
>> - //
>> - // Consider this example:
>> - // char *p = (char*)malloc(100)
>> - // char *q = p+80;
>> - //
>> - // In the context of c1 and c2, the "object" pointed by q refers to the
>> - // stretch of memory of q[0:19]. So, getObjectSize(q) should return 20.
>> - //
>> - // However, in the context of c3, the "object" refers to the chunk of memory
>> - // being allocated. So, the "object" has 100 bytes, and q points to the middle
>> - // the "object". In case q is passed to isObjectSmallerThan() as the 1st
>> - // parameter, before the llvm::getObjectSize() is called to get the size of
>> - // entire object, we should:
>> - // - either rewind the pointer q to the base-address of the object in
>> - // question (in this case rewind to p), or
>> - // - just give up. It is up to caller to make sure the pointer is pointing
>> - // to the base address the object.
>> - //
>> - // We go for 2nd option for simplicity.
>> - if (!isIdentifiedObject(V))
>> - return false;
>> -
>> // This function needs to use the aligned object size because we allow
>> // reads a bit past the end given sufficient alignment.
>> uint64_t ObjectSize = getObjectSize(V, TD, TLI, /*RoundToAlign*/true);
>>
>> Modified: llvm/trunk/lib/Analysis/MemoryBuiltins.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MemoryBuiltins.cpp?rev=176407&r1=176406&r2=176407&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Analysis/MemoryBuiltins.cpp (original)
>> +++ llvm/trunk/lib/Analysis/MemoryBuiltins.cpp Sat Mar 2 05:23:34 2013
>> @@ -360,6 +360,26 @@ bool llvm::getObjectSize(const Value *Pt
>> return true;
>> }
>>
>> +/// \brief Compute the size of the underlying object pointed by Ptr. Returns
>> +/// true and the object size in Size if successful, and false otherwise.
>> +/// If RoundToAlign is true, then Size is rounded up to the aligment of allocas,
>> +/// byval arguments, and global variables.
>> +bool llvm::getUnderlyingObjectSize(const Value *Ptr, uint64_t &Size,
>> + const DataLayout *TD,
>> + const TargetLibraryInfo *TLI,
>> + bool RoundToAlign) {
>> + if (!TD)
>> + return false;
>> +
>> + ObjectSizeOffsetVisitor Visitor(TD, TLI, Ptr->getContext(), RoundToAlign);
>> + SizeOffsetType Data = Visitor.compute(const_cast<Value*>(Ptr));
>> + if (!Visitor.knownSize(Data))
>> + return false;
>> +
>> + Size = Data.first.getZExtValue();
>> + return true;
>> +}
>> +
>>
>> STATISTIC(ObjectVisitorArgument,
>> "Number of arguments with unsolved size and offset");
>>
>>
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