`unchecked_{shl|shr}` should use `u32` as the RHS #103456

scottmcm · 2022-10-24T00:08:07Z

The other shift methods, such as https://doc.rust-lang.org/nightly/std/primitive.u64.html#method.checked_shr and https://doc.rust-lang.org/nightly/std/primitive.i16.html#method.wrapping_shl, use u32 for the shift amount. That's consistent with other things, like count_ones, which also always use u32 for a bit count, regardless of the size of the type.

This PR changes unchecked_shl and unchecked_shr to also use u32 for the shift amount (rather than Self).

cc #85122, the unchecked_math tracking issue

rust-highfive · 2022-10-24T00:08:10Z

r? @joshtriplett

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scottmcm · 2022-10-24T00:10:00Z

src/test/codegen/unchecked_shifts.rs

+#[no_mangle]
+pub unsafe fn unchecked_shl_unsigned_same(a: u32, b: u32) -> u32 {
+    // CHECK-NOT: and i32
+    // CHECK: shl i32 %a, %b


annot: the LLVM instruction always gives poison by default for too-high shift amounts (https://llvm.org/docs/LangRef.html#shl-instruction), so no extra flags are expected in the IR.

scottmcm · 2022-10-24T00:11:06Z

library/core/src/num/int_macros.rs

@@ -1383,11 +1386,12 @@ macro_rules! int_impl {
        #[must_use = "this returns the result of the operation, \
                      without modifying the original"]
        #[inline(always)]
+        #[rustc_allow_const_fn_unstable(const_inherent_unchecked_arith)]


annot: this was previously using the intrinsic on stable, so the rustc_allow_const_fn_unstable isn't exposing anything new to stable here.

scottmcm · 2022-10-24T00:12:08Z

library/core/src/num/int_macros.rs

            // SAFETY: the caller must uphold the safety contract for
            // `unchecked_shl`.
-            unsafe { intrinsics::unchecked_shl(self, rhs) }
+            // Any legal shift amount is losslessly representable in the self type.
+            unsafe { intrinsics::unchecked_shl(self, rhs.try_into().ok().unwrap_unchecked()) }


annot: the .ok() looks silly here, but Result::unwrap_unchecked isn't const, whereas Option::unwrap_unchecked is const.

scottmcm · 2022-11-15T03:11:38Z

Hi libs-api! I'm nominating this one to get a 👍/👎 on the signature change, in hopes of then being able to move it to a less-busy reviewer once the API decision is made.

m-ou-se · 2022-11-15T11:48:51Z

@bors r+

bors · 2022-11-15T11:48:53Z

📌 Commit 3b16c04 has been approved by m-ou-se

It is now in the queue for this repository.

…-ou-se `unchecked_{shl|shr}` should use `u32` as the RHS The other shift methods, such as https://doc.rust-lang.org/nightly/std/primitive.u64.html#method.checked_shr and https://doc.rust-lang.org/nightly/std/primitive.i16.html#method.wrapping_shl, use `u32` for the shift amount. That's consistent with other things, like `count_ones`, which also always use `u32` for a bit count, regardless of the size of the type. This PR changes `unchecked_shl` and `unchecked_shr` to also use `u32` for the shift amount (rather than Self). cc rust-lang#85122, the `unchecked_math` tracking issue

scottmcm · 2022-11-16T07:22:18Z

@bors rollup=iffy (failed in a rollup once, but with the update that config worked in CI)
@bors r-

Failed in rollup https://github.com/rust-lang-ci/rust/actions/runs/3477142652/jobs/5813017785

scottmcm · 2022-11-17T00:45:13Z

Did the test-in-CI trick, and it doesn't fail that config any more: https://github.com/rust-lang/rust/actions/runs/3484161910/jobs/5828408349

@bors r+

bors · 2022-11-17T00:45:14Z

📌 Commit 9d4b1f9 has been approved by scottmcm

It is now in the queue for this repository.

bors · 2022-11-17T00:45:15Z

🌲 The tree is currently closed for pull requests below priority 1. This pull request will be tested once the tree is reopened.

…cottmcm `unchecked_{shl|shr}` should use `u32` as the RHS The other shift methods, such as https://doc.rust-lang.org/nightly/std/primitive.u64.html#method.checked_shr and https://doc.rust-lang.org/nightly/std/primitive.i16.html#method.wrapping_shl, use `u32` for the shift amount. That's consistent with other things, like `count_ones`, which also always use `u32` for a bit count, regardless of the size of the type. This PR changes `unchecked_shl` and `unchecked_shr` to also use `u32` for the shift amount (rather than Self). cc rust-lang#85122, the `unchecked_math` tracking issue

…earth Rollup of 8 pull requests Successful merges: - rust-lang#102977 (remove HRTB from `[T]::is_sorted_by{,_key}`) - rust-lang#103378 (Fix mod_inv termination for the last iteration) - rust-lang#103456 (`unchecked_{shl|shr}` should use `u32` as the RHS) - rust-lang#103701 (Simplify some pointer method implementations) - rust-lang#104047 (Diagnostics `icu4x` based list formatting.) - rust-lang#104338 (Enforce that `dyn*` coercions are actually pointer-sized) - rust-lang#104498 (Edit docs for `rustc_errors::Handler::stash_diagnostic`) - rust-lang#104556 (rustdoc: use `code-header` class to format enum variants) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

rust-highfive assigned joshtriplett Oct 24, 2022

rustbot added the T-libs Relevant to the library team, which will review and decide on the PR/issue. label Oct 24, 2022

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 24, 2022

scottmcm commented Oct 24, 2022

View reviewed changes

unchecked_{shl|shr} should use u32 as the RHS

3b16c04

scottmcm force-pushed the fix-unchecked-shifts branch from debadbc to 3b16c04 Compare October 24, 2022 00:33

scottmcm mentioned this pull request Oct 24, 2022

Tracking Issue for inherent unchecked integer methods #85122

Open

20 tasks

scottmcm added T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. and removed T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Oct 25, 2022

scottmcm added the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Nov 15, 2022

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 15, 2022

m-ou-se removed the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Nov 15, 2022

scottmcm assigned m-ou-se and unassigned joshtriplett Nov 16, 2022

Dylan-DPC mentioned this pull request Nov 16, 2022

Rollup of 9 pull requests #104479

Closed

bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Nov 16, 2022

Ignore the unchecked-shifts codegen test in debug-assertions builds

9d4b1f9

rustbot added the A-testsuite Area: The testsuite used to check the correctness of rustc label Nov 17, 2022

rustbot added the T-infra Relevant to the infrastructure team, which will review and decide on the PR/issue. label Nov 17, 2022

scottmcm force-pushed the fix-unchecked-shifts branch 2 times, most recently from 1e783ac to 9d4b1f9 Compare November 17, 2022 00:44

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Nov 17, 2022

Manishearth mentioned this pull request Nov 18, 2022

Rollup of 9 pull requests #104585

Closed

This was referenced Nov 18, 2022

Rollup of 8 pull requests #104589

Closed

Rollup of 8 pull requests #104591

Merged

bors merged commit e230115 into rust-lang:master Nov 19, 2022

rustbot added this to the 1.67.0 milestone Nov 19, 2022

scottmcm deleted the fix-unchecked-shifts branch November 19, 2022 03:31

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`unchecked_{shl|shr}` should use `u32` as the RHS #103456

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