aarch64 llvm 14 regression with vectors: assertion `TmpVec.size() > 1' failed

[andrewrk]

Does not affect LLVM 13.0.1.
Tested with LLVM 14.0.6. Have not yet confirmed whether it affects trunk.

Reduced LLVM IR:

define internal fastcc i16 @test2.doTheTest.S.doTheTest() {
Block10:
  %0 = call fastcc i16 undef(<3 x i32> zeroinitializer, <3 x i32> zeroinitializer)
  ret i16 0
}

Reproduction:

$ ~/local/llvm14-debug/bin/clang -c reduced.ll -target aarch64-linux-unknown
warning: overriding the module target triple with aarch64-unknown-linux-unknown [-Woverride-module]
clang: /home/andy/Downloads/llvm-project-14/llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp:656: llvm::MachineInstrBuilder llvm::MachineIRBuilder::buildUnmerge(llvm::ArrayRef<llvm::Register>, const llvm::SrcOp&): Assertion `TmpVec.size() > 1' failed.

Downstream issue: ziglang/zig#12012

Apologies for not catching this during the RC phase.

[llvmbot]

@llvm/issue-subscribers-bug

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

[DavidSpickett]

This issue first appears after 29f88b9.

It is present on main (which is at 1ee533afd0a64d7e021eb2b5ad6aa1a7722023cf as I write this).

Just to be sure, using fastisel there is no problem:

$ ninja clang && ./bin/clang -c /tmp/test.ll  -target aarch64-linux-unknown -mllvm -fast-isel
ninja: no work to do.
warning: overriding the module target triple with aarch64-unknown-linux-unknown [-Woverride-module]
1 warning generated.

[DavidSpickett]

@petar-avramovic

[petar-avramovic]

Will look into this, reproduces on O0 only
llc -global-isel -mtriple=aarch64-unknown-linux-unknown -verify-machineinstrs -O0

• @aemerson for awareness

[petar-avramovic]

Fix: https://reviews.llvm.org/D129194

[nikic]

Looks like the fix landed in 2483f43.