[PATCH] D140939: [X86] Transform AtomicRMW logic operations to BT{R|C|S} if only changing/testing a single bit.
Alexander Kornienko via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Jan 23 03:52:38 PST 2023
alexfh added a comment.
In D140939#4072755 <https://reviews.llvm.org/D140939#4072755>, @goldstein.w.n wrote:
> In D140939#4072672 <https://reviews.llvm.org/D140939#4072672>, @goldstein.w.n wrote:
>
>> In D140939#4072488 <https://reviews.llvm.org/D140939#4072488>, @alexfh wrote:
>>
>>> In D140939#4072474 <https://reviews.llvm.org/D140939#4072474>, @alexfh wrote:
>>>
>>>> In D140939#4072473 <https://reviews.llvm.org/D140939#4072473>, @alexfh wrote:
>>>>
>>>>> Unfortunately, there's another problem, which doesn't get fixed by https://reviews.llvm.org/D142166 / 2e25204779e5b972d668bf66a0014c1325813b35 <https://reviews.llvm.org/rG2e25204779e5b972d668bf66a0014c1325813b35>:
>>>>>
>>>>> assert.h assertion failed at llvm/lib/Target/X86/X86ISelLowering.cpp:31466 in std::pair<Value *, BitTestKind> FindSingleBitChange(Value *): I != nullptr
>>>>> @ 0x56257abc9524 __assert_fail
>>>>> @ 0x562578c7fd1c FindSingleBitChange()
>>>>> @ 0x562578c7f6dd llvm::X86TargetLowering::shouldExpandLogicAtomicRMWInIR()
>>>>> @ 0x562578c8098b llvm::X86TargetLowering::shouldExpandAtomicRMWInIR()
>>>>> @ 0x5625790a6099 (anonymous namespace)::AtomicExpand::tryExpandAtomicRMW()
>>>>> @ 0x5625790a59dd (anonymous namespace)::AtomicExpand::runOnFunction()
>>>>> @ 0x56257a86e87d llvm::FPPassManager::runOnFunction()
>>>>> @ 0x56257a876104 llvm::FPPassManager::runOnModule()
>>>>> @ 0x56257a86ef7c llvm::legacy::PassManagerImpl::run()
>>>>> @ 0x562575bad581 clang::EmitBackendOutput()
>>>>> @ 0x562575baabe9 clang::BackendConsumer::HandleTranslationUnit()
>>>>> @ 0x562576a85e5c clang::ParseAST()
>>>>> @ 0x5625767cbf23 clang::FrontendAction::Execute()
>>>>> @ 0x562576741cad clang::CompilerInstance::ExecuteAction()
>>>>> @ 0x5625757871e8 clang::ExecuteCompilerInvocation()
>>>>> @ 0x56257577ae41 cc1_main()
>>>>> @ 0x562575776ec8 ExecuteCC1Tool()
>>>>> @ 0x5625768ed317 llvm::function_ref<>::callback_fn<>()
>>>>> @ 0x56257aa23d20 llvm::CrashRecoveryContext::RunSafely()
>>>>> @ 0x5625768ecb63 clang::driver::CC1Command::Execute()
>>>>> @ 0x5625768ab2e6 clang::driver::Compilation::ExecuteCommand()
>>>>> @ 0x5625768ab60f clang::driver::Compilation::ExecuteJobs()
>>>>> @ 0x5625768caf70 clang::driver::Driver::ExecuteCompilation()
>>>>> @ 0x562575776027 clang_main()
>>>>> @ 0x7f8f04be3633 __libc_start_main
>>>>> @ 0x562575772bea _start
>>>>
>>>> I'd suggest to revert while investigating. I'm working on an isolated test case.
>>>
>>>
>>>
>>> $ cat reduced.ll
>>> target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
>>> target triple = "x86_64-unknown-linux-gnu"
>>>
>>> define weak_odr void @f() {
>>> entry:
>>> br label %if.end19
>>>
>>> cont11: ; No predecessors!
>>> %not = xor i32 0, -1
>>> %0 = atomicrmw and ptr null, i32 %not monotonic, align 4
>>> %and13 = and i32 %0, 0
>>> br label %if.end19
>>>
>>> if.end19: ; preds = %cont11, %entry
>>> ret void
>>> }
>>> $ ./good-clang -c reduced.ll -o good.o
>>> $ ./bad-clang -c reduced.ll -o bad.o
>>> assert.h assertion failed at llvm/lib/Target/X86/X86ISelLowering.cpp:31466 in std::pair<Value *, BitTestKind> FindSingleBitChange(Value *): I != nullptr
>>> @ 0x559d015c9524 __assert_fail
>>> @ 0x559cff67fd1c FindSingleBitChange()
>>> @ 0x559cff67f6dd llvm::X86TargetLowering::shouldExpandLogicAtomicRMWInIR()
>>> @ 0x559cff68098b llvm::X86TargetLowering::shouldExpandAtomicRMWInIR()
>>> @ 0x559cffaa6099 (anonymous namespace)::AtomicExpand::tryExpandAtomicRMW()
>>> @ 0x559cffaa59dd (anonymous namespace)::AtomicExpand::runOnFunction()
>>> @ 0x559d0126e87d llvm::FPPassManager::runOnFunction()
>>> @ 0x559d01276104 llvm::FPPassManager::runOnModule()
>>> @ 0x559d0126ef7c llvm::legacy::PassManagerImpl::run()
>>> @ 0x559cfc5ad581 clang::EmitBackendOutput()
>>> @ 0x559cfc5a94f8 clang::CodeGenAction::ExecuteAction()
>>> @ 0x559cfd1cbf23 clang::FrontendAction::Execute()
>>> @ 0x559cfd141cad clang::CompilerInstance::ExecuteAction()
>>> @ 0x559cfc1871e8 clang::ExecuteCompilerInvocation()
>>> @ 0x559cfc17ae41 cc1_main()
>>
>> Thank you for finding the case. A another one (and probably more realistic one is):
>>
>> define weak_odr void @f(i32 %0) {
>> entry:
>> br label %if.end19
>>
>> cont11: ; No predecessors!
>> %not = xor i32 %0, -1
>> %1 = atomicrmw and ptr null, i32 %not monotonic, align 4
>> %and13 = and i32 %1, 0
>> br label %if.end19
>>
>> if.end19: ; preds = %cont11, %entry
>> ret void
>> }
>>
>> So the fix is:
>>
>> - assert(I != nullptr);
>> +
>> + // If constant it will fold and we can evaluate later. If its an argument
>> + // or something of that nature, we can't analyze.
>> + if (I == nullptr)
>> + return {nullptr, UndefBit};
>>
>> I'm happy to post that as a patch.
>
> Created: https://reviews.llvm.org/D142339
>
> But let me know if revert is still preferable (I say as much there).
>
>> If you still want to revert, however, happy to do so as well and then repost the full version.
>>
>> Whichever you think is more prudent.
We're seeing a ton of fallout due to this, and given that there are already two different patterns that cause crashes, I'd like to have a known good version in the tree before we play whack-a-mole ;). Thus, I'd prefer that you reverted this and then recommitted with your proposed fix.
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https://reviews.llvm.org/D140939/new/
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