[BUG] Fatal error in clang when building with -O2 on arm64

[Rakashazi]

Description

I've run into the error below when compiling a particular file with -O2 on the arm64 ABI. It doesn't happen with -O1 or -O3 on arm64, and no problems with -O2 on the same file with other ABIs. Preprocessed source and run script are also attached: bug.zip

fatal error: error in backend: Cannot select: 0x62a2a28: v4i16 = AArch64ISD::DUP 0x62ab698, ./src/vice/vicii/vicii-draw.c:1490:24 @[ ./src/vice/vicii/vicii-draw.c:1509:5 ]
0x62ab698: i16 = truncate 0x62ab700, ./src/vice/vicii/vicii-draw.c:1490:24 @[ ./src/vice/vicii/vicii-draw.c:1509:5 ]
0x62ab700: i32,ch = CopyFromReg 0x61be328, Register:i32 %7, ./src/vice/vicii/vicii-draw.c:1489:13 @[ ./src/vice/vicii/vicii-draw.c:1509:5 ]
0x62aaf48: i32 = Register %7
In function: vicii_draw_init
clang: error: clang frontend command failed with exit code 70 (use -v to see invocation)
Android (5900059 based on r365631c) clang version 9.0.8 (https://android.googlesource.com/toolchain/llvm-project 207d7abc1a2abf3ef8d4301736d6a7ebc224a290) (based on LLVM 9.0.8svn)
Target: aarch64-none-linux-android21
Thread model: posix
InstalledDir: /opt/android-sdk-update-manager/ndk/21.1.6210238/toolchains/llvm/prebuilt/linux-x86_64/bin
clang: note: diagnostic msg: PLEASE submit a bug report to https://github.com/android-ndk/ndk/issues and include the crash backtrace, preprocessed source, and associated run script.

Environment Details

• NDK Version: 21.1.6210238-beta1
• Build system: Custom
• Host OS: Gentoo Linux
• ABI: arm64-v8a
• NDK API level: 21

[DanAlbert]

If it's quick to find the fix to cherry-pick, I think we can do this in r21b, otherwise this'll get moved to r21c.

[pirama-arumuga-nainar]

Reproduces with ToT as well. Get the same error as the original report. Debug build gives the following assertion:

clang++: /ssd2/pirama/llvm-monorepo/monorepo/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp:978: 
void (anonymous namespace)::SelectionDAGLegalize::LegalizeOp(llvm::SDNode *): Assertion `(TLI.ge
tTypeAction(*DAG.getContext(), Op.getValueType()) == TargetLowering::TypeLegal || Op.getOpcode()
 == ISD::TargetConstant || Op.getOpcode() == ISD::Register) && "Unexpected illegal type!"' faile
d.

[pirama-arumuga-nainar]

Thanks to @gburgessiv for reducing the repro to the following. Need to test this with r20 to see if this is a regression.

clang++ -cc1 -triple aarch64-none-linux-android21 -emit-obj -O2 -vectorize-loops vicii-draw-d6b435.reduced.c

void a() {
  int c, d, b;
  char *e;
  for (;; d++)
    for (; b <= 5; b++) {
      c = 0;
      for (; c <= 15; c++) {
        e[0] = d;
        e[1] = c & 4 ?: b;
        e[2] = e[3] = c ?: b;
        e += 4;
      }
    }
}

[gburgessiv]

Looks like LLVM 38a0616c1df029aff481eb0224dacb55c317865e (aka r357161) is where this crash started occurring. Given that ToT is ~30K commits beyond that ATM, new sources might've been introduced in the meantime.

[stephenhines]

Per https://github.com/android/ndk/wiki/NDK-Release-Process, this is a Medium severity issue, so we should fix this for the next LTS toolchain update.

[DanAlbert]

Yep, it's already been moved to r21c.

[stephenhines]

We need to get this into the LTS branch and then ship that in order to fully close this.

[stephenhines]

I'll cherry-pick it to llvm-r365631.

[pirama-arumuga-nainar]

🤦‍♂ Thanks for noticing the auto-close.

[stephenhines]

https://android-review.googlesource.com/c/toolchain/llvm-project/+/1263179 has the patch.