Debuginfo generation is broken with LLVM 3.8

[nagisa]

Compiling librustc_mir with optimisations on and debuginfo enabled fails with LLVM assertion:

piece is larger than or outside of variable
  call void @llvm.dbg.declare(metadata %"13.rustc::mir::visit::LvalueContext"* %arg1.sroa.2, metadata !24020, metadata !43416), !dbg !46046
!24020 = !DILocalVariable(arg: 4, scope: !24006, file: !1194, line: 1, type: !"{struct rustc/599ae68a7dffd6c9bf8d7a7e26afb91619ab5f582f32707f1893ef9e2fd1fdbd/94b2}")
!43416 = !DIExpression(DW_OP_bit_piece, 64, 192)
piece is larger than or outside of variable
  call void @llvm.dbg.declare(metadata %"13.rustc::mir::repr::Location"* %arg1.sroa.3, metadata !24020, metadata !46047), !dbg !46046
!24020 = !DILocalVariable(arg: 4, scope: !24006, file: !1194, line: 1, type: !"{struct rustc/599ae68a7dffd6c9bf8d7a7e26afb91619ab5f582f32707f1893ef9e2fd1fdbd/94b2}")
!46047 = !DIExpression(DW_OP_bit_piece, 256, 128)
LLVM ERROR: Broken module found, compilation aborted!

The failure started happening sometime in the past month. Any change related to how we generate debuginfo for variables is a suspect as it likely specifies the size of the variable incorrectly (as per https://llvm.org/bugs/show_bug.cgi?id=23712)

Works fine with LLVM bundled with rust.

[nagisa]

This is a regression-from-stable-to-nightly (-beta in a few days) and and I-ICE.

[cuviper]

I'm not sure which stable you meant, but I'm seeing this regression on stable 1.12 while building git2 for cargo, while compiling the same with 1.11 is fine. Here's the excerpt from Fedora's full build.log:

piece covers entire variable
  call void @llvm.dbg.value(metadata i64 %1, i64 0, metadata !10414, metadata !31684), !dbg !34307
!10414 = !DILocalVariable(arg: 3, scope: !10403, file: !10404, line: 1977, type: !"{struct git2/bd2b4ed1a06da7fa58e6c6d8f6516e398bfeede5c10924aaad59e63a932b47a7/b9f}")
!31684 = !DIExpression(DW_OP_bit_piece, 0, 64)
piece is larger than or outside of variable
  call void @llvm.dbg.value(metadata i64 %2, i64 0, metadata !10414, metadata !31685), !dbg !34307
!10414 = !DILocalVariable(arg: 3, scope: !10403, file: !10404, line: 1977, type: !"{struct git2/bd2b4ed1a06da7fa58e6c6d8f6516e398bfeede5c10924aaad59e63a932b47a7/b9f}")
!31685 = !DIExpression(DW_OP_bit_piece, 64, 64)
piece is larger than or outside of variable
  call void @llvm.dbg.declare(metadata %"2.std::option::Option<diff::DiffHunk>"* %arg1.sroa.2, metadata !10429, metadata !34312), !dbg !34313
!10429 = !DILocalVariable(arg: 4, scope: !10418, file: !10404, line: 1977, type: !"{struct git2/bd2b4ed1a06da7fa58e6c6d8f6516e398bfeede5c10924aaad59e63a932b47a7/b9b}")
!34312 = !DIExpression(DW_OP_bit_piece, 64, 128)
piece covers entire variable
  call void @llvm.dbg.value(metadata i64 %1, i64 0, metadata !10429, metadata !31684), !dbg !34313
!10429 = !DILocalVariable(arg: 4, scope: !10418, file: !10404, line: 1977, type: !"{struct git2/bd2b4ed1a06da7fa58e6c6d8f6516e398bfeede5c10924aaad59e63a932b47a7/b9b}")
!31684 = !DIExpression(DW_OP_bit_piece, 0, 64)
piece is larger than or outside of variable
  call void @llvm.dbg.value(metadata i64 %3, i64 0, metadata !10429, metadata !34315), !dbg !34313
!10429 = !DILocalVariable(arg: 4, scope: !10418, file: !10404, line: 1977, type: !"{struct git2/bd2b4ed1a06da7fa58e6c6d8f6516e398bfeede5c10924aaad59e63a932b47a7/b9b}")
!34315 = !DIExpression(DW_OP_bit_piece, 192, 64)
piece covers entire variable
  call void @llvm.dbg.value(metadata i64 %1, i64 0, metadata !10443, metadata !31684), !dbg !34318
!10443 = !DILocalVariable(arg: 3, scope: !10433, file: !10404, line: 1977, type: !"{struct git2/bd2b4ed1a06da7fa58e6c6d8f6516e398bfeede5c10924aaad59e63a932b47a7/ba5}")
!31684 = !DIExpression(DW_OP_bit_piece, 0, 64)
piece is larger than or outside of variable
  call void @llvm.dbg.value(metadata i64 %2, i64 0, metadata !10443, metadata !31685), !dbg !34318
!10443 = !DILocalVariable(arg: 3, scope: !10433, file: !10404, line: 1977, type: !"{struct git2/bd2b4ed1a06da7fa58e6c6d8f6516e398bfeede5c10924aaad59e63a932b47a7/ba5}")
!31685 = !DIExpression(DW_OP_bit_piece, 64, 64)
LLVM ERROR: Broken module found, compilation aborted!
Build failed, waiting for other jobs to finish...
error: Could not compile `git2`.
Caused by:
  Process didn't exit successfully: `rustc .cargo/registry/src/-059c64927a508553/git2-0.4.4/src/lib.rs --crate-name git2 --crate-type lib -C opt-level=3 --cfg feature="default" --cfg feature="https" --cfg feature="ssh" --cfg feature="libgit2-sys" -C metadata=6ff6b7061c01db01 -C extra-filename=-6ff6b7061c01db01 --out-dir /builddir/build/BUILD/cargo-0.13.0/target/x86_64-unknown-linux-gnu/release/deps --emit=dep-info,link --target x86_64-unknown-linux-gnu -L dependency=/builddir/build/BUILD/cargo-0.13.0/target/x86_64-unknown-linux-gnu/release/deps -L dependency=/builddir/build/BUILD/cargo-0.13.0/target/x86_64-unknown-linux-gnu/release/deps --extern url=/builddir/build/BUILD/cargo-0.13.0/target/x86_64-unknown-linux-gnu/release/deps/liburl-bf7ff6dce96f3de6.rlib --extern libc=/builddir/build/BUILD/cargo-0.13.0/target/x86_64-unknown-linux-gnu/release/deps/liblibc-d7f563bb6cbdc70a.rlib --extern bitflags=/builddir/build/BUILD/cargo-0.13.0/target/x86_64-unknown-linux-gnu/release/deps/libbitflags-877983b26a517965.rlib --extern libgit2_sys=/builddir/build/BUILD/cargo-0.13.0/target/x86_64-unknown-linux-gnu/release/deps/liblibgit2_sys-c6ac804eabc4dcd5.rlib --cap-lints allow -L native=/usr/lib64 -L native=/usr/lib64 -L native=/usr/lib64 -L native=/usr/lib64 -C opt-level=3 -g` (exit code: 1)

[cuviper]

I can also reproduce this compiling git2 with Rust 1.11 and RUSTFLAGS='-C opt-level=3 -g -Zorbit', using Fedora's same LLVM 3.8 in all cases. Even just opt-level=1 still fails, but 0 is ok.

[akien-mga]

I can confirm the error reported by @cuviper on Mageia too, using Rust 1.12.0 and LLVM 3.8.1, on both x86_64 and i586. The rust and cargo packaging in Mageia are otherwise synced with Fedora. Full build log on x86_64.

[cuviper]

I also just confirmed that 1.12 with -Zorbit=no builds fine, so it definitely looks like a MIR issue.

[nikomatsakis]

Tagging as regression. cc @rust-lang/compiler

[sanxiyn]

Bisecting from LLVM 3.8 to LLVM 3.9 led to r267296. That is, r267295 errors, and r267296 does not.

[brson]

Thanks for bisecting @sanxiyn