[LV] " VPlan cost model and legacy cost model disagreed" regression #160345
Description
We're seeing a good number of downstream ICEs from a change around 2025-09-22. Here is one reduced issue from Neoverse-V1 (and more from Neoverse-V2 are coming):
[scrubbed ~]$ cat new.ll
target triple = "aarch64-unknown-linux-gnu"
define void @foo() local_unnamed_addr #0 {
br i1 poison, label %.lr.ph, label %._crit_edge
.lr.ph: ; preds = %13, %0
%1 = phi i64 [ %15, %13 ], [ poison, %0 ]
%2 = phi i32 [ %14, %13 ], [ 1, %0 ]
%3 = add nsw i32 %2, -1
%4 = srem i32 %3, poison
%5 = add nsw i32 %4, 1
%6 = icmp eq i32 %5, poison
br i1 %6, label %7, label %13
7: ; preds = %.lr.ph
%8 = sdiv i32 %3, poison
%9 = add i32 %8, 1
%10 = sext i32 %9 to i64
%11 = getelementptr i32, ptr poison, i64 %10
%12 = getelementptr i8, ptr %11, i64 -4
store i32 %2, ptr %12, align 4
br label %13
13: ; preds = %7, %.lr.ph
%14 = add nuw nsw i32 %2, 1
%15 = add nsw i64 %1, -1
%16 = icmp sgt i64 %1, 1
br i1 %16, label %.lr.ph, label %._crit_edge
._crit_edge: ; preds = %13, %0
ret void
}
attributes #0 = { "target-cpu"="neoverse-v1" }
[scrubbed ~]$ opt --passes=loop-vectorize new.ll -S
opt: /scrubbed/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:7090: llvm::VectorizationFactor llvm::LoopVectorizationPlanner::computeBestVF(): Assertion `(BestFactor.Width == LegacyVF.Width || BestPlan.hasEarlyExit() || planContainsAdditionalSimplifications(getPlanFor(BestFactor.Width), CostCtx, OrigLoop, BestFactor.Width) || planContainsAdditionalSimplifications( getPlanFor(LegacyVF.Width), CostCtx, OrigLoop, LegacyVF.Width)) && " VPlan cost model and legacy cost model disagreed"' 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 --passes=loop-vectorize new.ll -S
1. Running pass "function(loop-vectorize<no-interleave-forced-only;no-vectorize-forced-only;>)" on module "new.ll"
2. Running pass "loop-vectorize<no-interleave-forced-only;no-vectorize-forced-only;>" on function "foo"
#0 0x0000000001bf3d48 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (opt+0x1bf3d48)
#1 0x0000000001bf0e70 llvm::sys::RunSignalHandlers() (opt+0x1bf0e70)
#2 0x0000000001bf0ff4 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
#3 0x000040001ee507a0 (linux-vdso.so.1+0x7a0)
#4 0x000040001f106274 raise (/lib64/libc.so.6+0x36274)
#5 0x000040001f0f0a2c abort (/lib64/libc.so.6+0x20a2c)
#6 0x000040001f0ffba0 __assert_fail_base (/lib64/libc.so.6+0x2fba0)
#7 0x000040001f0ffc18 __assert_perror_fail (/lib64/libc.so.6+0x2fc18)
#8 0x0000000003990f70 llvm::LoopVectorizationPlanner::computeBestVF() (opt+0x3990f70)
#9 0x000000000399c02c llvm::LoopVectorizePass::processLoop(llvm::Loop*) (opt+0x399c02c)
#10 0x000000000399e420 llvm::LoopVectorizePass::runImpl(llvm::Function&) (opt+0x399e420)
#11 0x000000000399e9e0 llvm::LoopVectorizePass::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (opt+0x399e9e0)
#12 0x00000000034b2d88 llvm::detail::PassModel<llvm::Function, llvm::LoopVectorizePass, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) PassBuilder.cpp:0:0
#13 0x0000000001e9e81c llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (opt+0x1e9e81c)
#14 0x0000000002dd7418 llvm::detail::PassModel<llvm::Function, llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function>>, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) NVPTXTargetMachine.cpp:0:0
#15 0x0000000001e9d008 llvm::ModuleToFunctionPassAdaptor::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (opt+0x1e9d008)
#16 0x0000000002dd73c8 llvm::detail::PassModel<llvm::Module, llvm::ModuleToFunctionPassAdaptor, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) NVPTXTargetMachine.cpp:0:0
#17 0x0000000001e9ca74 llvm::PassManager<llvm::Module, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (opt+0x1e9ca74)
#18 0x0000000003360278 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) (opt+0x3360278)
#19 0x0000000001bd662c optMain (opt+0x1bd662c)
#20 0x000040001f0f4384 __libc_start_main (/lib64/libc.so.6+0x24384)
#21 0x0000000001bcb2c4 _start (opt+0x1bcb2c4)
Aborted (core dumped)