[llvm] r243500 - ignore duplicate divisor uses when transforming into reciprocal multiplies (PR24141)

[Hans Wennborg]

Thanks everyone! Merged in
http://llvm.org/viewvc/llvm-project?rev=243524&view=rev

Sanjay: there were merge conflicts due to r243293 not being in the
branch. Can you double check that I got it right?

On Tue, Jul 28, 2015 at 10:03 PM, Owen Anderson <resistor at mac.com> wrote:
> OK to merge.
>
> —Owen
>
>> On Jul 28, 2015, at 6:00 PM, Hans Wennborg <hans at chromium.org> wrote:
>>
>> We should probably merge this to 3.7.
>>
>> Owen, you're the owner here. OK to merge?
>>
>> On Tue, Jul 28, 2015 at 4:28 PM, Sanjay Patel <spatel at rotateright.com> wrote:
>>> Author: spatel
>>> Date: Tue Jul 28 18:28:22 2015
>>> New Revision: 243500
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=243500&view=rev
>>> Log:
>>> ignore duplicate divisor uses when transforming into reciprocal multiplies (PR24141)
>>>
>>> PR24141: https://llvm.org/bugs/show_bug.cgi?id=24141
>>> contains a test case where we have duplicate entries in a node's uses() list.
>>>
>>> After r241826, we use CombineTo() to delete dead nodes when combining the uses into
>>> reciprocal multiplies, but this fails if we encounter the just-deleted node again in
>>> the list.
>>>
>>> The solution in this patch is to not add duplicate entries to the list of users that
>>> we will subsequently iterate over. For the test case, this avoids triggering the
>>> combine divisors logic entirely because there really is only one user of the divisor.
>>>
>>> Differential Revision: http://reviews.llvm.org/D11345
>>>
>>>
>>> Modified:
>>>    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
>>>    llvm/trunk/test/CodeGen/X86/fdiv-combine.ll
>>>
>>> Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=243500&r1=243499&r2=243500&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
>>> +++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Tue Jul 28 18:28:22 2015
>>> @@ -8261,11 +8261,11 @@ SDValue DAGCombiner::combineRepeatedFPDi
>>>     return SDValue();
>>>
>>>   // Find all FDIV users of the same divisor.
>>> -  SmallVector<SDNode *, 4> Users;
>>> -  for (auto *U : N1->uses()) {
>>> +  // Use a set because duplicates may be present in the user list.
>>> +  SetVector<SDNode *> Users;
>>> +  for (auto *U : N1->uses())
>>>     if (U->getOpcode() == ISD::FDIV && U->getOperand(1) == N1)
>>> -      Users.push_back(U);
>>> -  }
>>> +      Users.insert(U);
>>>
>>>   // Now that we have the actual number of divisor uses, make sure it meets
>>>   // the minimum threshold specified by the target.
>>>
>>> Modified: llvm/trunk/test/CodeGen/X86/fdiv-combine.ll
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/fdiv-combine.ll?rev=243500&r1=243499&r2=243500&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/test/CodeGen/X86/fdiv-combine.ll (original)
>>> +++ llvm/trunk/test/CodeGen/X86/fdiv-combine.ll Tue Jul 28 18:28:22 2015
>>> @@ -44,5 +44,24 @@ define double @div3_arcp(double %x, doub
>>>   ret double %ret
>>> }
>>>
>>> +define void @PR24141() #0 {
>>> +; CHECK-LABEL: PR24141:
>>> +; CHECK:       callq
>>> +; CHECK-NEXT:  divsd
>>> +; CHECK-NEXT:  jmp
>>> +entry:
>>> +  br label %while.body
>>> +
>>> +while.body:
>>> +  %x.0 = phi double [ undef, %entry ], [ %div, %while.body ]
>>> +  %call = call { double, double } @g(double %x.0)
>>> +  %xv0 = extractvalue { double, double } %call, 0
>>> +  %xv1 = extractvalue { double, double } %call, 1
>>> +  %div = fdiv double %xv0, %xv1
>>> +  br label %while.body
>>> +}
>>> +
>>> +declare { double, double } @g(double)
>>> +
>>> ; FIXME: If the backend understands 'arcp', then this attribute is unnecessary.
>>> attributes #0 = { "unsafe-fp-math"="true" }
>>>
>>>
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>