[ppc] Assertion `hasValue() && "Cannot get the value bit index of a constant bit"' failed

[cuviper]

Bugzilla Link	41088
Resolution	FIXED
Resolved on	Jan 29, 2020 13:00
Version	8.0
OS	Linux
Blocks	#40566
Attachments	bytecode reduced from rust #58996
CC	@nemanjai,@tstellar

Extended Description

Rust is seeing a bootstrap failure compiling itself for powerpc64 with LLVM assertions enabled.

rust-lang/rust#58996

rustc: /checkout/src/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:1114: unsigned int {anonymous}::BitPermutationSelector::ValueBit::getValueBitIndex() const: Assertion `hasValue() && "Cannot get the value bit index of a constant bit"' failed.

I collected the bytecode from this, and I found that the assertion can be reproduced with vanilla LLVM 8 and trunk, just by running llc. The attached file is the bugpoint reduction. It compiles fine with LLVM 7, so I bisected the crash and found r344347/D48025 (llvm-project commit 9552dd1).

https://reviews.llvm.org/D48025

On that commit, the backtrace looks like this:

• ./bin/llc /home/jistone/llvm-project/bugpoint-reduced-function.bc
  llc: /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:1115: unsigned int {anonymous}::BitPermutationSelector::ValueBit::getValueBitIndex() const: Assertion `hasValue() && "Cannot get the value bit index of a constant bit"' failed.
  Stack dump:

0.  Program arguments: ./bin/llc /home/jistone/llvm-project/bugpoint-reduced-function.bc
   

1.  Running pass 'Function Pass Manager' on module '/home/jistone/llvm-project/bugpoint-reduced-function.bc'.
   

2.  Running pass 'PowerPC DAG->DAG Pattern Instruction Selection' on function '@"_ZN132_$LT$rustc..ty..layout..LayoutCx$LT$$u27$tcx$C$$u20$rustc..ty..context..TyCtxt$LT$$u27$a$C$$u20$$u27$tcx$C$$u20$$u27$tcx$GT$$GT$$GT$19layout_raw_uncached17h9e786af8095bbf87E"'
   

#​0 0x000000000159791a llvm::sys::PrintStackTrace(llvm::raw_ostream&) /home/jistone/llvm-project/llvm/lib/Support/Unix/Signals.inc:494:3
#​1 0x0000000001595ea4 llvm::sys::RunSignalHandlers() /home/jistone/llvm-project/llvm/lib/Support/Signals.cpp:67:5
#​2 0x0000000001596005 SignalHandler(int) /home/jistone/llvm-project/llvm/lib/Support/Unix/Signals.inc:353:1
#​3 0x00007efc0e9b4030 __restore_rt (/lib64/libpthread.so.0+0x13030)
#​4 0x00007efc0e48153f __GI_raise (/lib64/libc.so.6+0x3853f)
#​5 0x00007efc0e46b895 __GI_abort (/lib64/libc.so.6+0x22895)
#​6 0x00007efc0e46b769 _nl_load_domain.cold.0 (/lib64/libc.so.6+0x22769)
#​7 0x00007efc0e4799f6 (/lib64/libc.so.6+0x309f6)
#​8 0x00000000008dbe5e llvm::SDNode::getValueType(unsigned int) const /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:1115:7
#​9 0x00000000008dbe5e llvm::SDValue::getValueType() const /home/jistone/llvm-project/llvm/include/llvm/CodeGen/SelectionDAGNodes.h:1110:34
#​10 0x00000000008dbe5e (anonymous namespace)::BitPermutationSelector::getValueBits(llvm::SDValue, unsigned int) /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:1318:26
#​11 0x00000000008db6f7 (anonymous namespace)::BitPermutationSelector::getValueBits(llvm::SDValue, unsigned int) /usr/include/c++/8/tuple:1605:5
#​12 0x00000000008dbb12 (anonymous namespace)::BitPermutationSelector::getValueBits(llvm::SDValue, unsigned int) /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:1218:9
#​13 0x00000000008dddc9 Select /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:2342:71
#​14 0x00000000008dddc9 tryBitPermutation /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:3599:33
#​15 0x00000000008dddc9 (anonymous namespace)::PPCDAGToDAGISel::Select(llvm::SDNode*) /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:4203:24
#​16 0x0000000001464273 llvm::SmallVectorTemplateCommon<llvm::SDNode*, void>::begin() /home/jistone/llvm-project/llvm/include/llvm/ADT/SmallVector.h:851:3
#​17 0x0000000001464273 llvm::SmallVectorTemplateCommon<llvm::SDNode*, void>::end() /home/jistone/llvm-project/llvm/include/llvm/ADT/SmallVector.h:133:35
#​18 0x0000000001464273 _ZN4llvm11SmallVectorIPNS_6SDNodeELj4EED4Ev /home/jistone/llvm-project/llvm/include/llvm/ADT/SmallVector.h:853:5
#​19 0x0000000001464273 llvm::SelectionDAGISel::DoInstructionSelection() /home/jistone/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:1066:32
#​20 0x000000000146ab2c _ZN4llvm10TimeRegionD4Ev /home/jistone/llvm-project/llvm/include/llvm/Support/Timer.h:161:8
#​21 0x000000000146ab2c _ZN4llvm16NamedRegionTimerD4Ev /home/jistone/llvm-project/llvm/include/llvm/Support/Timer.h:161:8
#​22 0x000000000146ab2c llvm::SelectionDAGISel::CodeGenAndEmitDAG() /home/jistone/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:905:61
#​23 0x000000000146fed7 llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) /home/jistone/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:1752:7
#​24 0x0000000001471c9a llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) (.part.971) /home/jistone/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:470:3
#​25 0x00000000008e49d9 (anonymous namespace)::PPCDAGToDAGISel::runOnMachineFunction(llvm::MachineFunction&) /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:155:7
#​26 0x0000000000c9135e llvm::MachineFunctionPass::runOnFunction(llvm::Function&) /home/jistone/llvm-project/llvm/lib/CodeGen/MachineFunctionPass.cpp:74:33
#​27 0x0000000000c9135e llvm::MachineFunctionPass::runOnFunction(llvm::Function&) /home/jistone/llvm-project/llvm/lib/CodeGen/MachineFunctionPass.cpp:39:6
#​28 0x0000000000ff4c68 llvm::FPPassManager::runOnFunction(llvm::Function&) /home/jistone/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1644:40
#​29 0x0000000000ff4d49 llvm::ilist_node_impl<llvm::ilist_detail::node_options<llvm::Function, true, false, void> >::getNext() /home/jistone/llvm-project/llvm/include/llvm/ADT/ilist_node.h:67:66
#​30 0x0000000000ff4d49 llvm::ilist_iterator<llvm::ilist_detail::node_options<llvm::Function, true, false, void>, false, false>::operator++() /home/jistone/llvm-project/llvm/include/llvm/ADT/ilist_iterator.h:159:25
#​31 0x0000000000ff4d49 llvm::FPPassManager::runOnModule(llvm::Module&) /home/jistone/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1678:22
#​32 0x0000000000ff40f8 runOnModule /home/jistone/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1745:7
#​33 0x0000000000ff40f8 llvm::legacy::PassManagerImpl::run(llvm::Module&) /home/jistone/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1857:55
#​34 0x00000000005c249c compileModule /home/jistone/llvm-project/llvm/tools/llc/llc.cpp:599:5
#​35 0x00000000005c249c main /home/jistone/llvm-project/llvm/tools/llc/llc.cpp:351:35
#​36 0x00007efc0e46d413 __libc_start_main (/lib64/libc.so.6+0x24413)
#​37 0x0000000000601eae _start (./bin/llc+0x601eae)

[cuviper]

assigned to @nemanjai

[cuviper]

Here is better backtrace context from a Debug build:

#​9 0x00000000013501ef (anonymous namespace)::BitPermutationSelector::ValueBit::getValueBitIndex() const /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:1115:7
#​10 0x0000000001352776 (anonymous namespace)::BitPermutationSelector::getValueBits(llvm::SDValue, unsigned int) /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:1349:19
#​11 0x000000000135227a (anonymous namespace)::BitPermutationSelector::getValueBits(llvm::SDValue, unsigned int) /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:1325:67
#​12 0x000000000135099f (anonymous namespace)::BitPermutationSelector::getValueBits(llvm::SDValue, unsigned int) /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:1216:69
#​13 0x00000000013591c4 (anonymous namespace)::BitPermutationSelector::Select(llvm::SDNode*) /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:2342:71
#​14 0x00000000013618e5 (anonymous namespace)::PPCDAGToDAGISel::tryBitPermutation(llvm::SDNode*) /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:3599:33
#​15 0x0000000001364f94 (anonymous namespace)::PPCDAGToDAGISel::Select(llvm::SDNode*) /home/jistone/llvm-project/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:4203:3
#​16 0x000000000246b62e llvm::SelectionDAGISel::DoInstructionSelection() /home/jistone/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:1066:32

That frame #​10 is here:

1347 // These bits are known to be zero.
1348 for (unsigned i = NumValidBits; i < NumBits; ++i)
1349 Bits[i] = ValueBit((*LHSBits)[i].getValue(),
1350 (*LHSBits)[i].getValueBitIndex(),
1351 ValueBit::VariableKnownToBeZero);

This appears to be the only caller in this file that doesn't guard for hasValue() first -- presumably because of that "known" comment. However, in the debugger I see that this bit (with i = 8) is actually a ConstZero.

[llvmbot]

I also ran in to this. This is the basic block that causes the crash:

; :1760: ; preds = %1698, %1698
%1761 = load %"rustc_target::abi::TargetDataLayout", %"rustc_target::abi::TargetDataLayout"** %294, align 8, !nonnull !​25
%1762 = call i8 @​_ZN12rustc_target3abi16TargetDataLayout17ptr_sized_integer17h77410fe8a37bbc08E(%"rustc_target::abi::TargetDataLayout" noalias nonnull readonly align 8 dereferenceable(64) %1761), !range !​3297
%1763 = zext i8 %1762 to i24
%1764 = shl nuw nsw i24 %1763, 8
call fastcc void @"ZN132$LT$rustc..ty..layout..LayoutCx$LT$$u27$tcx$C$$u20$rustc..ty..context..TyCtxt$LT$$u27$a$C$$u20$$u27$tcx$C$$u20$$u27$tcx$GT$$GT$$GT$19layout_raw_uncached28_$u7b$$u7b$closure$u7d$$u7d$17h374cab55366a3a80E"(%"rustc_target::abi::Scalar"* noalias nocapture nonnull sret dereferenceable(48) %279, i64** noalias nonnull readonly align 8 dereferenceable(8) %293, i24 %1764)
br label %1807

[nemanjai]

It appears I missed this - so sorry about that. Is this still an issue?

[nemanjai]

Fix in https://reviews.llvm.org/D72038

[cuviper]

Thank you! I've confirmed that it fixes the Rust build with assertions.

[tstellar]

mentioned in issue #40566