[llvm] [InstCombine] Move alignment assumptions to the base of a gep if alignment is preserved (PR #203032)

Wed Jun 10 09:27:50 PDT 2026

dtcxzyw wrote:

The following correctness issue was found by [llvm-hackme](https://github.com/dtcxzyw/llvm-hackme).

<!-- llvm-hackme-state: bug_found -->
<!-- llvm-hackme-baseline: c54fae14c05d312bddd744c86bd894057ff5956d -->
<!-- llvm-hackme-head-sha: f7412474da69cd364f7cd0b7f2bd9d3b9fbf358b -->
<!-- llvm-hackme-patch-sha256: f9dd411b064ebcaab1ce2247ce6a2b8b8407f32fa0096df02139b2676b5a3dfc -->
<!-- llvm-hackme-kind: crash -->

This comment is generated by an automated correctness checking service designed to help identify critical correctness bugs (opt crashes or Alive2 miscompilations) and improve PR review efficiency under limited reviewer bandwidth.

## Reproducer

**Kind**: crash

**IR Reproducer**:
```llvm
; RUN: opt -passes=instcombine<no-verify-fixpoint> -S
target datalayout = "p:128:128"
target triple = "x86_64-unknown-linux-gnu"

define void @test(ptr %p) {
  %gep = getelementptr i8, ptr %p, i128 18446744073709551616
  call void @llvm.assume(i1 true) ["align"(ptr %gep, i64 16)]
  ret void
}
```

**Stacktrace**:
```
opt: ../llvm-project-pr/llvm/include/llvm/ADT/APInt.h:1566: uint64_t llvm::APInt::getZExtValue() const: Assertion `getActiveBits() <= 64 && "Too many bits for uint64_t"' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and instructions to reproduce the bug.
Stack dump:
0.	Program arguments: /llvm-hackme/work/llvm-hackme/llvm-build-pr/bin/opt -S -o /dev/null /tmp/tmpm_i0khkw.ll -passes=instcombine<no-verify-fixpoint>
1.	Running pass "function(instcombine<max-iterations=1;no-verify-fixpoint>)" on module "/tmp/tmpm_i0khkw.ll"
2.	Running pass "instcombine<max-iterations=1;no-verify-fixpoint>" on function "test"
 #0 0x00007ffff7e19fb2 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/lib/Support/Unix/Signals.inc:885:3
 #1 0x00007ffff7e16a7c llvm::sys::RunSignalHandlers() /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/lib/Support/Signals.cpp:108:20
 #2 0x00007ffff7e16c81 SignalHandler(int, siginfo_t*, void*) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/lib/Support/Unix/Signals.inc:448:14
 #3 0x00007ffff7a19520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007ffff7a6d9fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x00007ffff7a19476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x00007ffff79ff7f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x00007ffff79ff71b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x00007ffff7a10e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x00007fffee0ed9c2 llvm::ArrayRef<llvm::TypeSize>::operator[](unsigned long) const /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/ADT/ArrayRef.h:247:5
#10 0x00007fffee0ed9c2 llvm::ArrayRef<llvm::TypeSize>::operator[](unsigned long) const /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/ADT/ArrayRef.h:246:12
#11 0x00007fffee0ed9c2 llvm::StructLayout::getElementOffset(unsigned int) const /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/IR/DataLayout.h:776:34
#12 0x00007fffee0ed9c2 llvm::GEPOperator::getMaxPreservedAlignment(llvm::DataLayout const&) const /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/lib/IR/Operator.cpp:112:36
#13 0x00007fffef2dbef8 llvm::Align::value() const /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/Support/Alignment.h:77:60
#14 0x00007fffef2dbef8 llvm::operator>=(llvm::Align, unsigned long) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/Support/Alignment.h:236:19
#15 0x00007fffef2dbef8 llvm::InstCombinerImpl::visitCallInst(llvm::CallInst&) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp:3670:60
#16 0x00007fffef266a42 llvm::InstCombinerImpl::run() /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp:5931:36
#17 0x00007fffef267a82 combineInstructionsOverFunction(llvm::Function&, llvm::InstructionWorklist&, llvm::AAResults*, llvm::AssumptionCache&, llvm::TargetLibraryInfo&, llvm::TargetTransformInfo&, llvm::DominatorTree&, llvm::OptimizationRemarkEmitter&, llvm::BlockFrequencyInfo*, llvm::BranchProbabilityInfo*, llvm::ProfileSummaryInfo*, llvm::InstCombineOptions const&) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp:6235:5
#18 0x00007fffef2689cc llvm::InstCombinePass::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp:6296:3
#19 0x00007ffff14fcb26 llvm::detail::PassModel<llvm::Function, llvm::InstCombinePass, llvm::AnalysisManager<llvm::Function> >::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/IR/PassManagerInternal.h:94:3
#20 0x00007fffee0ffdad llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function> >::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/IR/PassManagerImpl.h:80:18
#21 0x00007ffff58d15b6 llvm::detail::PassModel<llvm::Function, llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function> >, llvm::AnalysisManager<llvm::Function> >::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/IR/PassManagerInternal.h:94:3
#22 0x00007fffee0fe851 llvm::ModuleToFunctionPassAdaptor::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/lib/IR/PassManager.cpp:132:41
#23 0x00007ffff7f85566 llvm::detail::PassModel<llvm::Module, llvm::ModuleToFunctionPassAdaptor, llvm::AnalysisManager<llvm::Module> >::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/IR/PassManagerInternal.h:94:3
#24 0x00007fffee0fee77 llvm::PassManager<llvm::Module, llvm::AnalysisManager<llvm::Module> >::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/IR/PassManagerImpl.h:80:18
#25 0x00007ffff7f9289f llvm::SmallPtrSetImplBase::~SmallPtrSetImplBase() /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/ADT/SmallPtrSet.h:89:5
#26 0x00007ffff7f9289f llvm::SmallPtrSetImpl<llvm::AnalysisKey*>::~SmallPtrSetImpl() /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/ADT/SmallPtrSet.h:366:35
#27 0x00007ffff7f9289f llvm::SmallPtrSet<llvm::AnalysisKey*, 2u>::~SmallPtrSet() /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/ADT/SmallPtrSet.h:533:7
#28 0x00007ffff7f9289f llvm::PreservedAnalyses::~PreservedAnalyses() /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/include/llvm/IR/Analysis.h:112:7
#29 0x00007ffff7f9289f llvm::runPassPipeline(llvm::StringRef, llvm::Module&, llvm::TargetMachine*, llvm::TargetLibraryInfoImpl*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::StringRef, llvm::ArrayRef<llvm::PassPlugin>, llvm::ArrayRef<std::function<void (llvm::PassBuilder&)> >, llvm::opt_tool::OutputKind, llvm::opt_tool::VerifierKind, bool, bool, bool, bool, bool, bool, bool, bool) /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/tools/opt/NewPMDriver.cpp:574:10
#30 0x00007ffff7f9f40c optMain /llvm-hackme/work/llvm-hackme/llvm-build-pr/../llvm-project-pr/llvm/tools/opt/optdriver.cpp:798:25
#31 0x00007ffff7a00d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#32 0x00007ffff7a00e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#33 0x0000555555555095 _start (/llvm-hackme/work/llvm-hackme/llvm-build-pr/bin/opt+0x1095)
```

**Baseline Revision**: `c54fae14c05d312bddd744c86bd894057ff5956d`
**PR Head SHA**: `f7412474da69cd364f7cd0b7f2bd9d3b9fbf358b`
**Patch SHA256**: `f9dd411b064ebcaab1ce2247ce6a2b8b8407f32fa0096df02139b2676b5a3dfc`

https://github.com/llvm/llvm-project/pull/203032