Use Itertools::all_equal_value() where applicable

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -1,3 +1,4 @@
+use itertools::Itertools as _;
 use rustc_abi::{self as abi, FIRST_VARIANT};
 use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::layout::{HasTyCtxt, HasTypingEnv, LayoutOf, TyAndLayout};
@@ -111,15 +112,14 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     let size = bx.const_usize(dest.layout.size.bytes());
 
                     // Use llvm.memset.p0i8.* to initialize all same byte arrays
-                    if let Some(int) = bx.cx().const_to_opt_u128(v, false) {
+                    if let Some(int) = bx.cx().const_to_opt_u128(v, false)
-                        let bytes = &int.to_le_bytes()[..cg_elem.layout.size.bytes_usize()];
+                        && let bytes = &int.to_le_bytes()[..cg_elem.layout.size.bytes_usize()]
-                        let first = bytes[0];
+                        && let Ok(&byte) = bytes.iter().all_equal_value()
-                        if bytes[1..].iter().all(|&b| b == first) {
+                    {
-                            let fill = bx.cx().const_u8(first);
+                        let fill = bx.cx().const_u8(byte);
                         bx.memset(start, fill, size, dest.val.align, MemFlags::empty());
                         return true;
                     }
-                    }
 
                     // Use llvm.memset.p0i8.* to initialize byte arrays
                     let v = bx.from_immediate(v);
@@ -130,14 +130,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     false
                 };
 
-                match cg_elem.val {
+                if let OperandValue::Immediate(v) = cg_elem.val
-                    OperandValue::Immediate(v) => {
+                    && try_init_all_same(bx, v)
-                        if try_init_all_same(bx, v) {
+                {
                     return;
                 }
-                    }
-                    _ => (),
-                }
 
                 let count = self
                     .monomorphize(count)

compiler/rustc_mir_transform/src/gvn.rs

@@ -87,6 +87,7 @@
 use std::borrow::Cow;
 
 use either::Either;
+use itertools::Itertools as _;
 use rustc_abi::{self as abi, BackendRepr, FIRST_VARIANT, FieldIdx, Primitive, Size, VariantIdx};
 use rustc_const_eval::const_eval::DummyMachine;
 use rustc_const_eval::interpret::{
@@ -1023,16 +1024,16 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             }
         };
 
-        if ty.is_array() && fields.len() > 4 {
+        if ty.is_array()
-            let first = fields[0];
+            && fields.len() > 4
-            if fields.iter().all(|&v| v == first) {
+            && let Ok(&first) = fields.iter().all_equal_value()
+        {
             let len = ty::Const::from_target_usize(self.tcx, fields.len().try_into().unwrap());
             if let Some(op) = self.try_as_operand(first, location) {
                 *rvalue = Rvalue::Repeat(op, len);
             }
             return Some(self.insert(ty, Value::Repeat(first, len)));
         }
-        }
 
         if let Some(value) =
             self.simplify_aggregate_to_copy(lhs, rvalue, location, &fields, variant_index)

compiler/rustc_mir_transform/src/lint_tail_expr_drop_order.rs

@@ -2,6 +2,7 @@ use std::cell::RefCell;
 use std::collections::hash_map;
 use std::rc::Rc;
 
+use itertools::Itertools as _;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
 use rustc_data_structures::unord::{UnordMap, UnordSet};
 use rustc_errors::Subdiagnostic;
@@ -339,9 +340,9 @@ pub(crate) fn run_lint<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId, body: &Body<
             // Suppose that all BIDs point into the same local,
             // we can remove the this local from the observed drops,
             // so that we can focus our diagnosis more on the others.
-            if candidates.iter().all(|&(_, place)| candidates[0].1.local == place.local) {
+            if let Ok(local) = candidates.iter().map(|&(_, place)| place.local).all_equal_value() {
                 for path_idx in all_locals_dropped.iter() {
-                    if move_data.move_paths[path_idx].place.local == candidates[0].1.local {
+                    if move_data.move_paths[path_idx].place.local == local {
                         to_exclude.insert(path_idx);
                     }
                 }

compiler/rustc_mir_transform/src/simplify.rs

@@ -34,6 +34,7 @@
 //! The normal logic that a program with UB can be changed to do anything does not apply to
 //! pre-"runtime" MIR!
 
+use itertools::Itertools as _;
 use rustc_index::{Idx, IndexSlice, IndexVec};
 use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::*;
@@ -288,19 +289,12 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
             return false;
         };
 
-        let first_succ = {
+        let Ok(first_succ) = terminator.successors().all_equal_value() else {
-            if let Some(first_succ) = terminator.successors().next() {
+            return false;
-                if terminator.successors().all(|s| s == first_succ) {
+        };
+
         let count = terminator.successors().count();
         self.pred_count[first_succ] -= (count - 1) as u32;
-                    first_succ
-                } else {
-                    return false;
-                }
-            } else {
-                return false;
-            }
-        };
 
         debug!("simplifying branch {:?}", terminator);
         terminator.kind = TerminatorKind::Goto { target: first_succ };

compiler/rustc_resolve/src/diagnostics.rs

@@ -1,3 +1,4 @@
+use itertools::Itertools as _;
 use rustc_ast::visit::{self, Visitor};
 use rustc_ast::{
     self as ast, CRATE_NODE_ID, Crate, ItemKind, ModKind, NodeId, Path, join_path_idents,
@@ -3469,16 +3470,11 @@ fn show_candidates(
                 err.note(note.to_string());
             }
         } else {
-            let (_, descr_first, _, _, _) = &inaccessible_path_strings[0];
+            let descr = inaccessible_path_strings
-            let descr = if inaccessible_path_strings
                 .iter()
-                .skip(1)
+                .map(|&(_, descr, _, _, _)| descr)
-                .all(|(_, descr, _, _, _)| descr == descr_first)
+                .all_equal_value()
-            {
+                .unwrap_or("item");
-                descr_first
-            } else {
-                "item"
-            };
             let plural_descr =
                 if descr.ends_with('s') { format!("{descr}es") } else { format!("{descr}s") };