[llvm] r242281 - [PM/AA] Fix *numerous* serious bugs in GlobalsModRef found by

[Sean Silva]

Added in r242356.

-- Sean Silva

On Wed, Jul 15, 2015 at 3:49 PM, Sean Silva <chisophugis at gmail.com> wrote:

>
>
> On Wed, Jul 15, 2015 at 2:18 PM, Chandler Carruth <chandlerc at gmail.com>
> wrote:
>
>> Awesome! Do you want to land that test case? If not, I will, but you may
>> get to it sooner at this point...
>>
>
> Sure, I'll do that now.
>
> -- Sean Silva
>
>
>>
>> On Wed, Jul 15, 2015 at 2:08 PM Sean Silva <chisophugis at gmail.com> wrote:
>>
>>> Thanks! I think this fixed PR23345; I didn't know about
>>> I.mayWriteToMemory()
>>>
>>> -- Sean Silva
>>>
>>> On Wed, Jul 15, 2015 at 1:53 AM, Chandler Carruth <chandlerc at gmail.com>
>>> wrote:
>>>
>>>> Author: chandlerc
>>>> Date: Wed Jul 15 03:53:29 2015
>>>> New Revision: 242281
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=242281&view=rev
>>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D242281-26view-3Drev&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=v_2U7OQd83CL4gchkkSZVU3fb0tMVRRG0j7MxIm2l1Q&s=FIjAFu91y9yQQlNOxBR3MNPtBoxckgBquFpcazgFFcc&e=>
>>>
>>>
>>>> Log:
>>>> [PM/AA] Fix *numerous* serious bugs in GlobalsModRef found by
>>>> inspection.
>>>>
>>>> While we want to handle calls specially in this code because they should
>>>> have been modeled by the call graph analysis that precedes it, we should
>>>> *not* be re-implementing the predicates for whether an instruction reads
>>>> or writes memory. Those are well defined already. Notably, at least the
>>>> following issues seem to be clearly missed before:
>>>> - Ordered atomic loads can "write" to memory by causing writes from
>>>> other
>>>>   threads to become visible. Similarly for ordered atomic stores.
>>>> - AtomicRMW instructions quite obviously both read and write to memory.
>>>> - AtomicCmpXchg instructions also read and write to memory.
>>>> - Fences read and write to memory.
>>>> - Invokes of intrinsics or memory allocation functions.
>>>>
>>>> I don't have any test cases, and I suspect this has never really come up
>>>> in the real world. But there is no reason why it wouldn't, and it makes
>>>> the code simpler to do this the right way.
>>>>
>>>> While here, I've tried to make the loops significantly simpler as well
>>>> and added helpful comments as to what is going on.
>>>>
>>>> Modified:
>>>>     llvm/trunk/lib/Analysis/IPA/GlobalsModRef.cpp
>>>>
>>>> Modified: llvm/trunk/lib/Analysis/IPA/GlobalsModRef.cpp
>>>>
>>> URL:
>>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/IPA/GlobalsModRef.cpp?rev=242281&r1=242280&r2=242281&view=diff
>>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_lib_Analysis_IPA_GlobalsModRef.cpp-3Frev-3D242281-26r1-3D242280-26r2-3D242281-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=v_2U7OQd83CL4gchkkSZVU3fb0tMVRRG0j7MxIm2l1Q&s=Q0Y9JUhRV2iEM7NdBl52tiz7eVvdznT8n2zfuYufLF0&e=>
>>>
>>>
>>>>
>>>> ==============================================================================
>>>> --- llvm/trunk/lib/Analysis/IPA/GlobalsModRef.cpp (original)
>>>> +++ llvm/trunk/lib/Analysis/IPA/GlobalsModRef.cpp Wed Jul 15 03:53:29
>>>> 2015
>>>> @@ -439,30 +439,39 @@ void GlobalsModRef::AnalyzeCallGraph(Cal
>>>>      }
>>>>
>>>>      // Scan the function bodies for explicit loads or stores.
>>>> -    for (unsigned i = 0, e = SCC.size(); i != e && FunctionEffect !=
>>>> ModRef;
>>>> -         ++i)
>>>> -      for (inst_iterator II = inst_begin(SCC[i]->getFunction()),
>>>> -                         E = inst_end(SCC[i]->getFunction());
>>>> -           II != E && FunctionEffect != ModRef; ++II)
>>>> -        if (LoadInst *LI = dyn_cast<LoadInst>(&*II)) {
>>>> +    for (auto *Node : SCC) {
>>>> +      if (FunctionEffect == ModRef)
>>>> +        break; // The mod/ref lattice saturates here.
>>>> +      for (Instruction &I : inst_range(Node->getFunction())) {
>>>> +        if (FunctionEffect == ModRef)
>>>> +          break; // The mod/ref lattice saturates here.
>>>> +
>>>> +        // We handle calls specially because the graph-relevant
>>>> aspects are
>>>> +        // handled above.
>>>> +        if (auto CS = CallSite(&I)) {
>>>> +          if (isAllocationFn(&I, TLI) || isFreeCall(&I, TLI)) {
>>>> +            // FIXME: It is completely unclear why this is necessary
>>>> and not
>>>> +            // handled by the above graph code.
>>>> +            FunctionEffect |= ModRef;
>>>> +          } else if (Function *Callee = CS.getCalledFunction()) {
>>>> +            // The callgraph doesn't include intrinsic calls.
>>>> +            if (Callee->isIntrinsic()) {
>>>> +              ModRefBehavior Behaviour =
>>>> +                  AliasAnalysis::getModRefBehavior(Callee);
>>>> +              FunctionEffect |= (Behaviour & ModRef);
>>>> +            }
>>>> +          }
>>>> +          continue;
>>>> +        }
>>>> +
>>>> +        // All non-call instructions we use the primary predicates for
>>>> whether
>>>> +        // thay read or write memory.
>>>> +        if (I.mayReadFromMemory())
>>>>            FunctionEffect |= Ref;
>>>> -          if (LI->isVolatile())
>>>> -            // Volatile loads may have side-effects, so mark them as
>>>> writing
>>>> -            // memory (for example, a flag inside the processor).
>>>> -            FunctionEffect |= Mod;
>>>> -        } else if (StoreInst *SI = dyn_cast<StoreInst>(&*II)) {
>>>> +        if (I.mayWriteToMemory())
>>>>            FunctionEffect |= Mod;
>>>> -          if (SI->isVolatile())
>>>> -            // Treat volatile stores as reading memory somewhere.
>>>> -            FunctionEffect |= Ref;
>>>> -        } else if (isAllocationFn(&*II, TLI) || isFreeCall(&*II, TLI))
>>>> {
>>>> -          FunctionEffect |= ModRef;
>>>> -        } else if (IntrinsicInst *Intrinsic =
>>>> dyn_cast<IntrinsicInst>(&*II)) {
>>>> -          // The callgraph doesn't include intrinsic calls.
>>>> -          Function *Callee = Intrinsic->getCalledFunction();
>>>> -          ModRefBehavior Behaviour =
>>>> AliasAnalysis::getModRefBehavior(Callee);
>>>> -          FunctionEffect |= (Behaviour & ModRef);
>>>> -        }
>>>> +      }
>>>> +    }
>>>>
>>>>      if ((FunctionEffect & Mod) == 0)
>>>>        ++NumReadMemFunctions;
>>>>
>>>>
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>>>>
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>>
>
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