[WIP] Implement `unchecked_disjoint_bitor` #124601

alion02 · 2024-05-02T02:25:03Z

AFAICT this doesn't compile right now (claims unrecognized intrinsic), and I don't exactly know why, because it did compile once already (or maybe there was a user error somehow). I would appreciate some help.

Beyond that this needs tests, non-intrinsic fns, and at least one todo resolved.

rustbot · 2024-05-02T02:25:10Z

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rustbot · 2024-05-02T02:25:12Z

Some changes occurred in rustc_ty_utils::consts.rs

cc @BoxyUwU

This PR changes Stable MIR

cc @oli-obk, @celinval, @ouz-a

This PR changes MIR

cc @oli-obk, @RalfJung, @JakobDegen, @davidtwco, @celinval, @vakaras

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

alion02 · 2024-05-02T02:42:06Z

Also, I think this PR will have to wait until the lowest supported LLVM is 18 or maybe even 19 (I can't figure out which version adds LLVMSetIsDisjoint, which seems necessary).

RalfJung · 2024-05-02T07:00:08Z

compiler/rustc_const_eval/src/interpret/operator.rs

@@ -308,6 +308,13 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 BitAnd => ImmTy::from_uint(l & r, left.layout),
 BitXor => ImmTy::from_uint(l ^ r, left.layout),

+ BitOrDisjoint => {
+ if l & r != 0 {
+ todo!(); // Can't figure out what to do here based on the surrounding code


You need to throw_ub!. To that end, you first need to add a new error variant to UndefinedBehaviorInfo, and then use that here.

Make sure to also add a Miri testcase that checks that we detect the UB here.

RalfJung · 2024-05-02T07:01:26Z

compiler/rustc_middle/src/mir/syntax.rs

@@ -1478,6 +1478,8 @@ pub enum BinOp {
 BitAnd,
 /// The `|` operator (bitwise or)
 BitOr,
+ /// Like `BitOr` and `BitXor`, but UB if results don't match.


Suggested change

/// Like `BitOr` and `BitXor`, but UB if results don't match.

/// Like `BitOr`, but UB if any bit is set both in the left and right operand (`left & right != 0`).

Let's express the requirement directly, in a way that matches the name, rather than indirectly.

RalfJung · 2024-05-02T07:01:51Z

Also, I think this PR will have to wait until the lowest supported LLVM is 18 or maybe even 19 (I can't figure out which version adds LLVMSetIsDisjoint, which seems necessary).

On older LLVM, it can simply compile to regular BitOr. We don't get optimization benefits but things will still compile correctly.

alion02 · 2024-05-03T01:18:34Z

On older LLVM, it can simply compile to regular BitOr.

Not sure how I'd do that. Do we have something like #[cfg(llvm_version = 17)]?

rust-log-analyzer · 2024-05-03T01:59:26Z

The job x86_64-gnu-llvm-17 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

#16 exporting to docker image format
#16 sending tarball 28.5s done
#16 DONE 40.6s
##[endgroup]
Setting extra environment values for docker:  --env ENABLE_GCC_CODEGEN=1 --env GCC_EXEC_PREFIX=/usr/lib/gcc/
[CI_JOB_NAME=x86_64-gnu-llvm-17]
---
sccache: Starting the server...
##[group]Configure the build
configure: processing command line
configure: 
configure: build.configure-args := ['--build=x86_64-unknown-linux-gnu', '--llvm-root=/usr/lib/llvm-17', '--enable-llvm-link-shared', '--set', 'rust.thin-lto-import-instr-limit=10', '--set', 'change-id=99999999', '--enable-verbose-configure', '--enable-sccache', '--disable-manage-submodules', '--enable-locked-deps', '--enable-cargo-native-static', '--set', 'rust.codegen-units-std=1', '--set', 'dist.compression-profile=balanced', '--dist-compression-formats=xz', '--disable-dist-src', '--release-channel=nightly', '--enable-debug-assertions', '--enable-overflow-checks', '--enable-llvm-assertions', '--set', 'rust.verify-llvm-ir', '--set', 'rust.codegen-backends=llvm,cranelift,gcc', '--set', 'llvm.static-libstdcpp', '--enable-new-symbol-mangling']
configure: target.x86_64-unknown-linux-gnu.llvm-config := /usr/lib/llvm-17/bin/llvm-config
configure: llvm.link-shared     := True
configure: rust.thin-lto-import-instr-limit := 10
configure: change-id            := 99999999
---
   Compiling rustc_driver_impl v0.0.0 (/checkout/compiler/rustc_driver_impl)
   Compiling rustc_driver v0.0.0 (/checkout/compiler/rustc_driver)
error: linking with `cc` failed: exit status: 1
  |
  = note: LC_ALL="C" PATH="/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-sysroot/lib/rustlib/x86_64-unknown-linux-gnu/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" VSLANG="1033" "cc" "-m64" "/tmp/rustcXOnmR0/symbols.o" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/rustc_main-0cbfe03da77376ae.rustc_main.bd086be8ad5323f2-cgu.0.rcgu.o" "-Wl,--as-needed" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/release/deps" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/build/psm-2415bf1bc99c7146/out" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/build/rustc_llvm-80e082dda5b39402/out" "-L" "/usr/lib/llvm-17/lib" "-L" "/usr/lib/gcc/x86_64-linux-gnu/13" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-sysroot/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps" "-Wl,-Bdynamic" "-lrustc_driver-54aa5590a1ff09f7" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-sysroot/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-lstd-db5ec79db612332a" "-Wl,-Bstatic" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-sysroot/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-f2b398c36a164e96.rlib" "-Wl,-Bdynamic" "-lLLVM-17" "-ldl" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-sysroot/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/rustc_main-0cbfe03da77376ae" "-Wl,--gc-sections" "-pie" "-Wl,-z,relro,-z,now" "-Wl,-O1" "-nodefaultlibs" "-Wl,-z,origin" "-Wl,-rpath,$ORIGIN/../lib"
  = note: /usr/bin/ld: /checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/librustc_driver-54aa5590a1ff09f7.so: undefined reference to `LLVMSetIsDisjoint'
          
          
  = note: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
  = note: use the `-l` flag to specify native libraries to link
  = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#rustc-link-lib)
error: could not compile `rustc-main` (bin "rustc-main") due to 1 previous error
Build completed unsuccessfully in 0:02:40
  local time: Fri May  3 01:59:16 UTC 2024
  network time: Fri, 03 May 2024 01:59:16 GMT

RalfJung · 2024-05-03T06:09:02Z

If you grep for LLVM_VERSION_GE in RustWrapper.cpp you can find existing examples.

alion02 added 8 commits May 1, 2024 06:10

Start implementation of disjoint_bitor

0879bbf

Add necessary FFI

5380e09

Add or disjoint to backend

9ae9862

Handle it in some of the places I can find

fbcb3dc

Comment out the intrinsic so rustc gets to scream at me

676d94b

Fix build

49a5f89

Finish adding intrinsic

e1e4c17

Fix name in docs

e62d5ce

rustbot assigned jieyouxu May 2, 2024

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels May 2, 2024

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alion02 marked this pull request as draft May 2, 2024 02:38

RalfJung reviewed May 2, 2024

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[WIP] Implement `unchecked_disjoint_bitor` #124601

[WIP] Implement `unchecked_disjoint_bitor` #124601

alion02 commented May 2, 2024 •

edited

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edited

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alion02 commented May 3, 2024

rust-log-analyzer commented May 3, 2024

RalfJung commented May 3, 2024

	/// Like `BitOr` and `BitXor`, but UB if results don't match.
	/// Like `BitOr`, but UB if any bit is set both in the left and right operand (`left & right != 0`).

[WIP] Implement unchecked_disjoint_bitor #124601

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[WIP] Implement unchecked_disjoint_bitor #124601

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RalfJung commented May 3, 2024

[WIP] Implement `unchecked_disjoint_bitor` #124601

[WIP] Implement `unchecked_disjoint_bitor` #124601

alion02 commented May 2, 2024 •

edited

alion02 commented May 2, 2024 •

edited