[llvm] r300657 - [JumpThread] We want to fold (not thread) when all predecessor go to single BB's successor. .
Xin Tong via llvm-commits
llvm-commits at lists.llvm.org
Wed Apr 19 08:14:31 PDT 2017
Thanks. I will take a look
-Xin
On Tue, Apr 18, 2017 at 11:28 PM Chandler Carruth <chandlerc at gmail.com>
wrote:
> This broke bootstrap stage2 with a pretty clear crash in jump threading:
>
> http://lab.llvm.org:8011/builders/clang-with-lto-ubuntu/builds/2476/steps/build-stage2-LLVMgold.so/logs/stdio
> http://bb.pgr.jp/builders/clang-3stage-x86_64-linux/builds/15036
>
> Reverting...
>
> On Tue, Apr 18, 2017 at 10:28 PM Xin Tong via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: trentxintong
>> Date: Wed Apr 19 00:15:57 2017
>> New Revision: 300657
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=300657&view=rev
>> Log:
>> [JumpThread] We want to fold (not thread) when all predecessor go to
>> single BB's successor. .
>>
>> Summary: In case all predecessor go to a single successor of current BB.
>> We want to fold (not thread).
>>
>> Reviewers: efriedma, sanjoy
>>
>> Reviewed By: sanjoy
>>
>> Subscribers: dberlin, majnemer, llvm-commits
>>
>> Differential Revision: https://reviews.llvm.org/D30869
>>
>> Modified:
>> llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
>> llvm/trunk/test/Transforms/JumpThreading/basic.ll
>>
>> Modified: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp?rev=300657&r1=300656&r2=300657&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp Wed Apr 19
>> 00:15:57 2017
>> @@ -1289,6 +1289,33 @@ bool JumpThreadingPass::ProcessThreadabl
>> if (PredToDestList.empty())
>> return false;
>>
>> + // If all the predecessors go to a single known successor, we want to
>> fold,
>> + // not thread. By doing so, we do not need to duplicate the current
>> block and
>> + // also miss potential opportunities in case we don't/can't duplicate.
>> + if (OnlyDest && OnlyDest != MultipleDestSentinel) {
>> + if (PredToDestList.size() ==
>> + (size_t)std::distance(pred_begin(BB), pred_end(BB))) {
>> + for (BasicBlock *SuccBB : successors(BB)) {
>> + if (SuccBB != OnlyDest)
>> + SuccBB->removePredecessor(BB, true); // This is unreachable
>> successor.
>> + }
>> +
>> + // Finally update the terminator.
>> + TerminatorInst *Term = BB->getTerminator();
>> + BranchInst::Create(OnlyDest, Term);
>> + Term->eraseFromParent();
>> +
>> + // If the condition is now dead due to the removal of the old
>> terminator,
>> + // erase it.
>> + auto *CondInst = dyn_cast<Instruction>(Cond);
>> + if (CondInst && CondInst->use_empty())
>> + CondInst->eraseFromParent();
>> + // FIXME: in case this instruction is defined in the current BB
>> and it
>> + // resolves to a single value from all predecessors, we can do
>> RAUW.
>> + return true;
>> + }
>> + }
>> +
>> // Determine which is the most common successor. If we have many
>> inputs and
>> // this block is a switch, we want to start by threading the batch
>> that goes
>> // to the most popular destination first. If we only know about one
>>
>> Modified: llvm/trunk/test/Transforms/JumpThreading/basic.ll
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/JumpThreading/basic.ll?rev=300657&r1=300656&r2=300657&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/JumpThreading/basic.ll (original)
>> +++ llvm/trunk/test/Transforms/JumpThreading/basic.ll Wed Apr 19 00:15:57
>> 2017
>> @@ -4,6 +4,95 @@ declare i32 @f1()
>> declare i32 @f2()
>> declare void @f3()
>>
>> +; Make sure we can fold this branch ... We will not be able to thread it
>> as
>> +; L0 is too big to duplicate. L2 is the unreachable block here.
>> +;
>> +; CHECK-LABEL: @test_br_folding_not_threading(
>> +; CHECK: L1:
>> +; CHECK: call i32 @f2()
>> +; CHECK: call void @f3()
>> +; CHECK-NEXT: ret void
>> +; CHECK-NOT: br
>> +; CHECK: L3:
>> +define void @test_br_folding_not_threading(i1 %cond) nounwind {
>> +entry:
>> + br i1 %cond, label %L0, label %L3
>> +L0:
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + br i1 %cond, label %L1, label %L2
>> +
>> +L1:
>> + call void @f3()
>> + ret void
>> +L2:
>> + call void @f3()
>> + ret void
>> +L3:
>> + call void @f3()
>> + ret void
>> +}
>> +
>> +
>> +; Make sure we can fold this branch ... We will not be able to thread it
>> as
>> +; L0 is too big to duplicate. L2 is the unreachable block here.
>> +; With more than 1 predecessors.
>> +;
>> +; CHECK-LABEL: @test_br_folding_not_threading_multiple_preds(
>> +; CHECK: L1:
>> +; CHECK: call i32 @f2()
>> +; CHECK: call void @f3()
>> +; CHECK-NEXT: ret void
>> +; CHECK-NOT: br
>> +; CHECK: L3:
>> +define void @test_br_folding_not_threading_multiple_preds(i1 %condx, i1
>> %cond) nounwind {
>> +entry:
>> + br i1 %condx, label %X0, label %X1
>> +
>> +X0:
>> + br i1 %cond, label %L0, label %L3
>> +
>> +X1:
>> + br i1 %cond, label %L0, label %L3
>> +
>> +L0:
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + call i32 @f2()
>> + br i1 %cond, label %L1, label %L2
>> +
>> +L1:
>> + call void @f3()
>> + ret void
>> +L2:
>> + call void @f3()
>> + ret void
>> +L3:
>> + call void @f3()
>> + ret void
>> +}
>> +
>> define i32 @test1(i1 %cond) {
>> ; CHECK-LABEL: @test1(
>>
>>
>>
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>>
> --
Software Engineer
Employee of Facebook Inc.
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