Android build fails with LLVM error

[mmatyas]

The Android build fails with the following error:

LLVM ERROR: Constant Island pass failed to converge!
Build failed, waiting for other jobs to finish...
error: Could not compile `cssparser`.

Caused by:
  Process didn't exit successfully: `rustc /home/mmatyas/Servo/servo-x64/servo/.cargo/registry/src/github.com-88ac128001ac3a9a/cssparser-0.5.5/src/lib.rs --crate-name cssparser --crate-type lib -C opt-level=3 -C codegen-units=4 --cfg feature="heap_size" --cfg feature="serde" --cfg feature="serde_macros" --cfg feature="serde-serialization" --cfg feature="heapsize_plugin" --cfg feature="heapsize" -C metadata=a00db9153a066bec -C extra-filename=-a00db9153a066bec --out-dir /home/mmatyas/Servo/servo-x64/servo/target/arm-linux-androideabi/release/deps --emit=dep-info,link --target arm-linux-androideabi -C ar=arm-linux-androideabi-ar -C linker=/home/mmatyas/Servo/servo-x64/servo/components/servo/./fake-ld.sh -L dependency=/home/mmatyas/Servo/servo-x64/servo/target/arm-linux-androideabi/release/deps -L dependency=/home/mmatyas/Servo/servo-x64/servo/target/arm-linux-androideabi/release/deps --extern heapsize_plugin=/home/mmatyas/Servo/servo-x64/servo/target/release/deps/libheapsize_plugin-00846447151e4ac3.so --extern serde_macros=/home/mmatyas/Servo/servo-x64/servo/target/release/deps/libserde_macros-c550fbd19e352e36.so --extern encoding=/home/mmatyas/Servo/servo-x64/servo/target/arm-linux-androideabi/release/deps/libencoding-8b01435d6d00d080.rlib --extern matches=/home/mmatyas/Servo/servo-x64/servo/target/arm-linux-androideabi/release/deps/libmatches-030a774745cc4f96.rlib --extern heapsize=/home/mmatyas/Servo/servo-x64/servo/target/arm-linux-androideabi/release/deps/libheapsize-6b0058e51ea0ec07.rlib --extern serde=/home/mmatyas/Servo/servo-x64/servo/target/arm-linux-androideabi/release/deps/libserde-3a777b14c091f0d1.rlib --cap-lints allow -C link-args=-fuse-ld=gold -C target-feature=+neon` (exit code: 1)

I've tried on multiple systems, on Ubuntu 15.10 and 14.04, using Android NDK r10d. Here's a Travis log: https://travis-ci.org/mmatyas/servo-nightly/jobs/122117906

[eddyb]

Error comes from an ARM-specific pass which can have its threshold increased, presumably by setting:

RUSTFLAGS="-C llvm-args=-arm-constant-island-max-iteration=100"

However, comments indicate this is an extreme case - could you get the output of that rustc command with --emit=llvm-ir?

[mmatyas]

Running RUSTFLAGS="-C llvm-args=-arm-constant-island-max-iteration=100" ./mach build -r --android results in

rustc: Unknown command line argument '-arm-constant-island-max-iteration=100'.  Try: 'rustc -help'
rustc: Did you mean '-mips-constant-islands-small-offset=100'?

and adding --emit=llvm-ir to the failing rustc command in the first post results in

cfgspec:1:9: 1:21 error: unexpected token: `serde_macros`
cfgspec:1 feature=serde_macros
                  ^~~~~~~~~~~~

[eddyb]

Oh, I didn't check the LLVM branch Rust uses, which hardcodes that limit (so the option was added since the last Rust LLVM update).

[eddyb]

Looks like https://llvm.org/bugs/show_bug.cgi?id=25339 which has been fixed late February and Rust needs a LLVM update to get the fix. cc @alexcrichton

[alexcrichton]

Ah yeah it should be fine to backport the fix to our LLVM branch (currently 2016-03-13) at the time of this writing.

[mmatyas]

Just a note, the error also occurred when I tried to cross compile to ARM with RUSTFLAGS=' -C target-feature=+neon'.

[fabricedesre]

Is someone actively working on the LLVM backport?

[mmatyas]

Looks like this got fixed, so I'm closing the issue.