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

[Chandler Carruth]

Awesome! Do you want to land that test case? If not, I will, but you may
get to it sooner at this point...

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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