Auto merge of rust-lang#140053 - ChrisDenton:rollup-tt00skl, r=ChrisDenton

Rollup of 7 pull requests

Successful merges:

 - rust-lang#139042 (Do not remove trivial `SwitchInt` in analysis MIR)
 - rust-lang#139533 (add next_index to Enumerate)
 - rust-lang#139843 (Setup editor file associations for non-rs extensions)
 - rust-lang#140000 (skip llvm-config in autodiff check builds, when its unavailable)
 - rust-lang#140008 (Improve `clean_maybe_renamed_item` function code a bit)
 - rust-lang#140024 (Remove early exits from JumpThreading.)
 - rust-lang#140039 (Add option for stable backport poll)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

Diff for: compiler/rustc_interface/src/tests.rs

@@ -818,8 +818,8 @@ fn test_unstable_options_tracking_hash() {
     tracked!(min_function_alignment, Some(Align::EIGHT));
     tracked!(mir_emit_retag, true);
     tracked!(mir_enable_passes, vec![("DestProp".to_string(), false)]);
-    tracked!(mir_keep_place_mention, true);
     tracked!(mir_opt_level, Some(4));
+    tracked!(mir_preserve_ub, true);
     tracked!(move_size_limit, Some(4096));
     tracked!(mutable_noalias, false);
     tracked!(next_solver, NextSolverConfig { coherence: true, globally: true });

Diff for: compiler/rustc_mir_transform/src/early_otherwise_branch.rs

@@ -223,7 +223,7 @@ impl<'tcx> crate::MirPass<'tcx> for EarlyOtherwiseBranch {
         // Since this optimization adds new basic blocks and invalidates others,
         // clean up the cfg to make it nicer for other passes
         if should_cleanup {
-            simplify_cfg(body);
+            simplify_cfg(tcx, body);
         }
     }
 

Diff for: compiler/rustc_mir_transform/src/inline.rs

@@ -63,7 +63,7 @@ impl<'tcx> crate::MirPass<'tcx> for Inline {
         let _guard = span.enter();
         if inline::<NormalInliner<'tcx>>(tcx, body) {
             debug!("running simplify cfg on {:?}", body.source);
-            simplify_cfg(body);
+            simplify_cfg(tcx, body);
             deref_finder(tcx, body);
         }
     }
@@ -99,7 +99,7 @@ impl<'tcx> crate::MirPass<'tcx> for ForceInline {
         let _guard = span.enter();
         if inline::<ForceInliner<'tcx>>(tcx, body) {
             debug!("running simplify cfg on {:?}", body.source);
-            simplify_cfg(body);
+            simplify_cfg(tcx, body);
             deref_finder(tcx, body);
         }
     }

Diff for: compiler/rustc_mir_transform/src/jump_threading.rs

@@ -43,7 +43,7 @@ impl<'tcx> crate::MirPass<'tcx> for MatchBranchSimplification {
         }
 
         if should_cleanup {
-            simplify_cfg(body);
+            simplify_cfg(tcx, body);
         }
     }
 

Diff for: compiler/rustc_mir_transform/src/match_branches.rs

@@ -8,7 +8,7 @@ pub(super) struct RemovePlaceMention;
 
 impl<'tcx> crate::MirPass<'tcx> for RemovePlaceMention {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        !sess.opts.unstable_opts.mir_keep_place_mention
+        !sess.opts.unstable_opts.mir_preserve_ub
     }
 
     fn run_pass(&self, _: TyCtxt<'tcx>, body: &mut Body<'tcx>) {

Diff for: compiler/rustc_mir_transform/src/remove_place_mention.rs

@@ -35,7 +35,7 @@ impl<'tcx> crate::MirPass<'tcx> for RemoveUnneededDrops {
         // if we applied optimizations, we potentially have some cfg to cleanup to
         // make it easier for further passes
         if should_simplify {
-            simplify_cfg(body);
+            simplify_cfg(tcx, body);
         }
     }
 

Diff for: compiler/rustc_mir_transform/src/remove_unneeded_drops.rs

@@ -26,6 +26,13 @@
 //! Here the block (`{ return; }`) has the return type `char`, rather than `()`, but the MIR we
 //! naively generate still contains the `_a = ()` write in the unreachable block "after" the
 //! return.
+//!
+//! **WARNING**: This is one of the few optimizations that runs on built and analysis MIR, and
+//! so its effects may affect the type-checking, borrow-checking, and other analysis of MIR.
+//! We must be extremely careful to only apply optimizations that preserve UB and all
+//! non-determinism, since changes here can affect which programs compile in an insta-stable way.
+//! The normal logic that a program with UB can be changed to do anything does not apply to
+//! pre-"runtime" MIR!
 
 use rustc_index::{Idx, IndexSlice, IndexVec};
 use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
@@ -66,8 +73,8 @@ impl SimplifyCfg {
     }
 }
 
-pub(super) fn simplify_cfg(body: &mut Body<'_>) {
-    CfgSimplifier::new(body).simplify();
+pub(super) fn simplify_cfg<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+    CfgSimplifier::new(tcx, body).simplify();
     remove_dead_blocks(body);
 
     // FIXME: Should probably be moved into some kind of pass manager
@@ -79,9 +86,9 @@ impl<'tcx> crate::MirPass<'tcx> for SimplifyCfg {
         self.name()
     }
 
-    fn run_pass(&self, _: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         debug!("SimplifyCfg({:?}) - simplifying {:?}", self.name(), body.source);
-        simplify_cfg(body);
+        simplify_cfg(tcx, body);
     }
 
     fn is_required(&self) -> bool {
@@ -90,12 +97,13 @@ impl<'tcx> crate::MirPass<'tcx> for SimplifyCfg {
 }
 
 struct CfgSimplifier<'a, 'tcx> {
+    preserve_switch_reads: bool,
     basic_blocks: &'a mut IndexSlice<BasicBlock, BasicBlockData<'tcx>>,
     pred_count: IndexVec<BasicBlock, u32>,
 }
 
 impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
-    fn new(body: &'a mut Body<'tcx>) -> Self {
+    fn new(tcx: TyCtxt<'tcx>, body: &'a mut Body<'tcx>) -> Self {
         let mut pred_count = IndexVec::from_elem(0u32, &body.basic_blocks);
 
         // we can't use mir.predecessors() here because that counts
@@ -110,9 +118,12 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
             }
         }
 
+        // Preserve `SwitchInt` reads on built and analysis MIR, or if `-Zmir-preserve-ub`.
+        let preserve_switch_reads = matches!(body.phase, MirPhase::Built | MirPhase::Analysis(_))
+            || tcx.sess.opts.unstable_opts.mir_preserve_ub;
         let basic_blocks = body.basic_blocks_mut();
 
-        CfgSimplifier { basic_blocks, pred_count }
+        CfgSimplifier { preserve_switch_reads, basic_blocks, pred_count }
     }
 
     fn simplify(mut self) {
@@ -253,9 +264,15 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
 
     // turn a branch with all successors identical to a goto
     fn simplify_branch(&mut self, terminator: &mut Terminator<'tcx>) -> bool {
-        match terminator.kind {
-            TerminatorKind::SwitchInt { .. } => {}
-            _ => return false,
+        // Removing a `SwitchInt` terminator may remove reads that result in UB,
+        // so we must not apply this optimization before borrowck or when
+        // `-Zmir-preserve-ub` is set.
+        if self.preserve_switch_reads {
+            return false;
+        }
+
+        let TerminatorKind::SwitchInt { .. } = terminator.kind else {
+            return false;
         };
 
         let first_succ = {

Diff for: compiler/rustc_mir_transform/src/simplify.rs

@@ -2322,12 +2322,12 @@ options! {
     mir_include_spans: MirIncludeSpans = (MirIncludeSpans::default(), parse_mir_include_spans, [UNTRACKED],
         "include extra comments in mir pretty printing, like line numbers and statement indices, \
          details about types, etc. (boolean for all passes, 'nll' to enable in NLL MIR only, default: 'nll')"),
-    mir_keep_place_mention: bool = (false, parse_bool, [TRACKED],
-        "keep place mention MIR statements, interpreted e.g., by miri; implies -Zmir-opt-level=0 \
-        (default: no)"),
     #[rustc_lint_opt_deny_field_access("use `Session::mir_opt_level` instead of this field")]
     mir_opt_level: Option<usize> = (None, parse_opt_number, [TRACKED],
         "MIR optimization level (0-4; default: 1 in non optimized builds and 2 in optimized builds)"),
+    mir_preserve_ub: bool = (false, parse_bool, [TRACKED],
+        "keep place mention statements and reads in trivial SwitchInt terminators, which are interpreted \
+        e.g., by miri; implies -Zmir-opt-level=0 (default: no)"),
     mir_strip_debuginfo: MirStripDebugInfo = (MirStripDebugInfo::None, parse_mir_strip_debuginfo, [TRACKED],
         "Whether to remove some of the MIR debug info from methods.  Default: None"),
     move_size_limit: Option<usize> = (None, parse_opt_number, [TRACKED],

Diff for: compiler/rustc_session/src/options.rs

@@ -23,6 +23,39 @@ impl<I> Enumerate<I> {
     pub(in crate::iter) fn new(iter: I) -> Enumerate<I> {
         Enumerate { iter, count: 0 }
     }
+
+    /// Retrieve the current position of the iterator.
+    ///
+    /// If the iterator has not advanced, the position returned will be 0.
+    ///
+    /// The position may also exceed the bounds of the iterator to allow for calculating
+    /// the displacement of the iterator from following calls to [`Iterator::next`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(next_index)]
+    ///
+    /// let arr = ['a', 'b'];
+    ///
+    /// let mut iter = arr.iter().enumerate();
+    ///
+    /// assert_eq!(iter.next_index(), 0);
+    /// assert_eq!(iter.next(), Some((0, &'a')));
+    ///
+    /// assert_eq!(iter.next_index(), 1);
+    /// assert_eq!(iter.next_index(), 1);
+    /// assert_eq!(iter.next(), Some((1, &'b')));
+    ///
+    /// assert_eq!(iter.next_index(), 2);
+    /// assert_eq!(iter.next(), None);
+    /// assert_eq!(iter.next_index(), 2);
+    /// ```
+    #[inline]
+    #[unstable(feature = "next_index", issue = "130711")]
+    pub fn next_index(&self) -> usize {
+        self.count
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

Diff for: library/core/src/iter/adapters/enumerate.rs

@@ -120,3 +120,13 @@ fn test_double_ended_enumerate() {
     assert_eq!(it.next_back(), Some((2, 3)));
     assert_eq!(it.next(), None);
 }
+
+#[test]
+fn test_empty_iterator_enumerate_next_index() {
+    let mut it = empty::<i32>().enumerate();
+    assert_eq!(it.next_index(), 0);
+    assert_eq!(it.next_index(), 0);
+    assert_eq!(it.next(), None);
+    assert_eq!(it.next_index(), 0);
+    assert_eq!(it.next_index(), 0);
+}

Diff for: library/coretests/tests/iter/adapters/enumerate.rs

@@ -63,6 +63,7 @@
 #![feature(maybe_uninit_write_slice)]
 #![feature(min_specialization)]
 #![feature(never_type)]
+#![feature(next_index)]
 #![feature(numfmt)]
 #![feature(pattern)]
 #![feature(pointer_is_aligned_to)]

Diff for: library/coretests/tests/lib.rs

@@ -1194,8 +1194,7 @@ pub fn rustc_cargo(
         let enzyme_dir = builder.build.out.join(arch).join("enzyme").join("lib");
         cargo.rustflag("-L").rustflag(enzyme_dir.to_str().expect("Invalid path"));
 
-        if !builder.config.dry_run() {
-            let llvm_config = builder.llvm_config(builder.config.build).unwrap();
+        if let Some(llvm_config) = builder.llvm_config(builder.config.build) {
             let llvm_version_major = llvm::get_llvm_version_major(builder, &llvm_config);
             cargo.rustflag("-l").rustflag(&format!("Enzyme-{llvm_version_major}"));
         }

Diff for: src/bootstrap/src/core/build_steps/compile.rs

@@ -584,6 +584,7 @@ Select which editor you would like to set up [default: None]: ";
                 "51068d4747a13732440d1a8b8f432603badb1864fa431d83d0fd4f8fa57039e0",
                 "d29af4d949bbe2371eac928a3c31cf9496b1701aa1c45f11cd6c759865ad5c45",
                 "b5dd299b93dca3ceeb9b335f929293cb3d4bf4977866fbe7ceeac2a8a9f99088",
+                "631c837b0e98ae35fd48b0e5f743b1ca60adadf2d0a2b23566ba25df372cf1a9",
             ],
             EditorKind::Helix => &[
                 "2d3069b8cf1b977e5d4023965eb6199597755e6c96c185ed5f2854f98b83d233",
@@ -602,10 +603,12 @@ Select which editor you would like to set up [default: None]: ";
                 "4eecb58a2168b252077369da446c30ed0e658301efe69691979d1ef0443928f4",
                 "c394386e6133bbf29ffd32c8af0bb3d4aac354cba9ee051f29612aa9350f8f8d",
                 "e53e9129ca5ee5dcbd6ec8b68c2d87376474eb154992deba3c6d9ab1703e0717",
+                "f954316090936c7e590c253ca9d524008375882fa13c5b41d7e2547a896ff893",
             ],
             EditorKind::Zed => &[
                 "bbce727c269d1bd0c98afef4d612eb4ce27aea3c3a8968c5f10b31affbc40b6c",
                 "a5380cf5dd9328731aecc5dfb240d16dac46ed272126b9728006151ef42f5909",
+                "2e96bf0d443852b12f016c8fc9840ab3d0a2b4fe0b0fb3a157e8d74d5e7e0e26",
             ],
         }
     }

Diff for: src/bootstrap/src/core/build_steps/setup.rs

@@ -8,10 +8,11 @@
                                                          "check"
                                                          "--json-output"])
                  :linkedProjects ["Cargo.toml"
-                                  "src/bootstrap/Cargo.toml"
-                                  "src/tools/rust-analyzer/Cargo.toml"
                                   "compiler/rustc_codegen_cranelift/Cargo.toml"
-                                  "compiler/rustc_codegen_gcc/Cargo.toml"]
+                                  "compiler/rustc_codegen_gcc/Cargo.toml"
+                                  "library/Cargo.toml"
+                                  "src/bootstrap/Cargo.toml"
+                                  "src/tools/rust-analyzer/Cargo.toml"]
                  :rustfmt ( :overrideCommand ["build/host/rustfmt/bin/rustfmt"
                                               "--edition=2021"])
                  :procMacro ( :server "build/host/stage0/libexec/rust-analyzer-proc-macro-srv"

Diff for: src/etc/rust_analyzer_eglot.el

@@ -9,11 +9,11 @@
     ],
     "rust-analyzer.linkedProjects": [
         "Cargo.toml",
+        "compiler/rustc_codegen_cranelift/Cargo.toml",
+        "compiler/rustc_codegen_gcc/Cargo.toml",
         "library/Cargo.toml",
         "src/bootstrap/Cargo.toml",
-        "src/tools/rust-analyzer/Cargo.toml",
-        "compiler/rustc_codegen_cranelift/Cargo.toml",
-        "compiler/rustc_codegen_gcc/Cargo.toml"
+        "src/tools/rust-analyzer/Cargo.toml"
     ],
     "rust-analyzer.rustfmt.overrideCommand": [
         "${workspaceFolder}/build/host/rustfmt/bin/rustfmt",
@@ -36,5 +36,10 @@
     },
     "rust-analyzer.server.extraEnv": {
         "RUSTUP_TOOLCHAIN": "nightly"
+    },
+    "files.associations": {
+        "*.fixed": "rust",
+        "*.pp": "rust",
+        "*.mir": "rust"
     }
 }

Diff for: src/etc/rust_analyzer_settings.json

@@ -21,15 +21,15 @@
         },
         "linkedProjects": [
           "Cargo.toml",
+          "compiler/rustc_codegen_cranelift/Cargo.toml",
+          "compiler/rustc_codegen_gcc/Cargo.toml",
           "library/Cargo.toml",
           "src/bootstrap/Cargo.toml",
-          "src/tools/rust-analyzer/Cargo.toml",
-          "compiler/rustc_codegen_cranelift/Cargo.toml",
-          "compiler/rustc_codegen_gcc/Cargo.toml"
+          "src/tools/rust-analyzer/Cargo.toml"
         ],
         "procMacro": {
-            "enable": true,
-            "server": "${workspaceFolder}/build/host/stage0/libexec/rust-analyzer-proc-macro-srv"
+          "enable": true,
+          "server": "${workspaceFolder}/build/host/stage0/libexec/rust-analyzer-proc-macro-srv"
         },
         "rustc": {
           "source": "./Cargo.toml"
@@ -47,5 +47,8 @@
         }
       }
     }
+  },
+  "file_types": {
+    "Rust": ["fixed", "pp", "mir"]
   }
 }