[llvm] [ValueTracking] Conservative nosync check prevents vectorization (PR #181345)

Sat Feb 14 05:58:55 PST 2026

kshitijvp wrote:

```define void @loop_contains_store_assumed_bounds(ptr noalias %array, ptr readonly %pred, i32 %n) {
; CHECK-LABEL: LV: Checking a loop in 'loop_contains_store_assumed_bounds'
; CHECK:       LV: Not vectorizing: Loop may fault.
entry:
  %n_bytes = mul nuw nsw i32 %n, 2
  call void @llvm.assume(i1 true) [ "align"(ptr %pred, i64 2), "dereferenceable"(ptr %pred, i32 %n_bytes) ]
  %tc = sext i32 %n to i64
  br label %for.body

for.body:
  %iv = phi i64 [ 0, %entry ], [ %iv.next, %for.inc ]
  %st.addr = getelementptr inbounds nuw i16, ptr %array, i64 %iv
  %data = load i16, ptr %st.addr, align 2
  %inc = add nsw i16 %data, 1
  store i16 %inc, ptr %st.addr, align 2
  %ee.addr = getelementptr inbounds nuw i16, ptr %pred, i64 %iv
  %ee.val = load i16, ptr %ee.addr, align 2
  %ee.cond = icmp sgt i16 %ee.val, 500
  br i1 %ee.cond, label %exit, label %for.inc

for.inc:
  %iv.next = add nuw nsw i64 %iv, 1
  %counted.cond = icmp eq i64 %iv.next, %tc
  br i1 %counted.cond, label %exit, label %for.body

exit:
  ret void
}
declare void @init_mem(ptr, i64);
declare i64 @get_an_unknown_offset();```

This test seems to cause assertion failure.
Attaching the stack dump:
```LV: Checking a loop in 'loop_contains_store_assumed_bounds' from input.ll
LV: Loop hints: force=? width=4 interleave=0
LV: Found a loop: for.body
LV: Found an induction variable.
opt: /home/kshitij/llvm-project/llvm/lib/Analysis/ScalarEvolution.cpp:3918: const llvm::SCEV* llvm::ScalarEvolution::getMinMaxExpr(llvm::SCEVTypes, llvm::SmallVectorImpl<const llvm::SCEV*>&): Assertion `getEffectiveSCEVType(Ops[i]->getType()) == ETy && "Operand types don't match!"' 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: opt -S -passes=loop-vectorize -debug-only=loop-vectorize -force-vector-width=4 -disable-output input.ll
1.	Running pass "function(loop-vectorize<no-interleave-forced-only;no-vectorize-forced-only;>)" on module "input.ll"
2.	Running pass "loop-vectorize<no-interleave-forced-only;no-vectorize-forced-only;>" on function "loop_contains_store_assumed_bounds"
 #0 0x000059bece3fe652 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/usr/local/bin/opt+0x4f44652)
 #1 0x000059bece3faf0f llvm::sys::RunSignalHandlers() (/usr/local/bin/opt+0x4f40f0f)
 #2 0x000059bece3fb05c SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
 #3 0x00007255cf245330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
 #4 0x00007255cf29eb2c __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
 #5 0x00007255cf29eb2c __pthread_kill_internal ./nptl/pthread_kill.c:78:10
 #6 0x00007255cf29eb2c pthread_kill ./nptl/pthread_kill.c:89:10
 #7 0x00007255cf24527e raise ./signal/../sysdeps/posix/raise.c:27:6
 #8 0x00007255cf2288ff abort ./stdlib/abort.c:81:7
 #9 0x00007255cf22881b _nl_load_domain ./intl/loadmsgcat.c:1177:9
#10 0x00007255cf23b517 (/lib/x86_64-linux-gnu/libc.so.6+0x3b517)
#11 0x000059bece7a3fdb llvm::ScalarEvolution::getMinMaxExpr(llvm::SCEVTypes, llvm::SmallVectorImpl<llvm::SCEV const*>&) (/usr/local/bin/opt+0x52e9fdb)
#12 0x000059bece7a4507 llvm::ScalarEvolution::getUMaxExpr(llvm::SCEV const*, llvm::SCEV const*) (/usr/local/bin/opt+0x52ea507)
#13 0x000059bece87c6c8 llvm::getStartAndEndForAccess(llvm::Loop const*, llvm::SCEV const*, llvm::Type*, llvm::SCEV const*, llvm::SCEV const*, llvm::ScalarEvolution*, llvm::DenseMap<std::pair<llvm::SCEV const*, llvm::Type*>, std::pair<llvm::SCEV const*, llvm::SCEV const*>, llvm::DenseMapInfo<std::pair<llvm::SCEV const*, llvm::Type*>, void>, llvm::detail::DenseMapPair<std::pair<llvm::SCEV const*, llvm::Type*>, std::pair<llvm::SCEV const*, llvm::SCEV const*>>>*, llvm::DominatorTree*, llvm::AssumptionCache*, std::optional<llvm::ScalarEvolution::LoopGuards>&) (/usr/local/bin/opt+0x53c26c8)
#14 0x000059bece8e002b llvm::isDereferenceableAndAlignedInLoop(llvm::LoadInst*, llvm::Loop*, llvm::ScalarEvolution&, llvm::DominatorTree&, llvm::AssumptionCache*, llvm::SmallVectorImpl<llvm::SCEVPredicate const*>*) (/usr/local/bin/opt+0x542602b)
#15 0x000059bed089a16a llvm::LoopVectorizationLegality::canUncountableExitConditionLoadBeMoved(llvm::BasicBlock*) (/usr/local/bin/opt+0x73e016a)
#16 0x000059bed089ae80 llvm::LoopVectorizationLegality::isVectorizableEarlyExitLoop() (/usr/local/bin/opt+0x73e0e80)
#17 0x000059bed08a4618 llvm::LoopVectorizationLegality::canVectorize(bool) (/usr/local/bin/opt+0x73ea618)
#18 0x000059bed082c8f3 llvm::LoopVectorizePass::processLoop(llvm::Loop*) (/usr/local/bin/opt+0x73728f3)
#19 0x000059bed0830dc1 llvm::LoopVectorizePass::runImpl(llvm::Function&) (/usr/local/bin/opt+0x7376dc1)
#20 0x000059bed0831480 llvm::LoopVectorizePass::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (/usr/local/bin/opt+0x7377480)
#21 0x000059bed05e1945 llvm::detail::PassModel<llvm::Function, llvm::LoopVectorizePass, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) PassBuilderPipelines.cpp:0:0
#22 0x000059bece6b8905 llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (/usr/local/bin/opt+0x51fe905)
#23 0x000059becfd77075 llvm::detail::PassModel<llvm::Function, llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function>>, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) AMDGPUTargetMachine.cpp:0:0
#24 0x000059bece6b7051 llvm::ModuleToFunctionPassAdaptor::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/usr/local/bin/opt+0x51fd051)
#25 0x000059becfd77715 llvm::detail::PassModel<llvm::Module, llvm::ModuleToFunctionPassAdaptor, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) AMDGPUTargetMachine.cpp:0:0
#26 0x000059bece6b783d llvm::PassManager<llvm::Module, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/usr/local/bin/opt+0x51fd83d)
#27 0x000059bed28f38c9 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) (/usr/local/bin/opt+0x94398c9)
#28 0x000059bece3df380 optMain (/usr/local/bin/opt+0x4f25380)
#29 0x00007255cf22a1ca __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:74:3
#30 0x00007255cf22a28b call_init ./csu/../csu/libc-start.c:128:20
#31 0x00007255cf22a28b __libc_start_main ./csu/../csu/libc-start.c:347:5
#32 0x000059bece3d09a5 _start (/usr/local/bin/opt+0x4f169a5)
```

https://github.com/llvm/llvm-project/pull/181345