Replace NormalizeArrayLen with GVN

GVN is actually on in release, and covers all the same things (or more), with `LowerSliceLen` changed to produce `PtrMetadata`.

Author: scottmcm

compiler/rustc_mir_transform/src/lib.rs

@@ -88,7 +88,6 @@ mod lower_slice_len;
 mod match_branches;
 mod mentioned_items;
 mod multiple_return_terminators;
-mod normalize_array_len;
 mod nrvo;
 mod prettify;
 mod promote_consts;
@@ -581,9 +580,6 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
             &o1(simplify::SimplifyCfg::AfterUnreachableEnumBranching),
             // Inlining may have introduced a lot of redundant code and a large move pattern.
             // Now, we need to shrink the generated MIR.
-
-            // Has to run after `slice::len` lowering
-            &normalize_array_len::NormalizeArrayLen,
             &ref_prop::ReferencePropagation,
             &sroa::ScalarReplacementOfAggregates,
             &match_branches::MatchBranchSimplification,

compiler/rustc_mir_transform/src/lower_slice_len.rs

@@ -1,10 +1,9 @@
-//! This pass lowers calls to core::slice::len to just Len op.
+//! This pass lowers calls to core::slice::len to just PtrMetadata op.
 //! It should run before inlining!
 
 use rustc_hir::def_id::DefId;
-use rustc_index::IndexSlice;
 use rustc_middle::mir::*;
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::TyCtxt;
 
 pub struct LowerSliceLenCalls;
 
@@ -29,16 +28,11 @@ pub fn lower_slice_len_calls<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let basic_blocks = body.basic_blocks.as_mut_preserves_cfg();
     for block in basic_blocks {
         // lower `<[_]>::len` calls
-        lower_slice_len_call(tcx, block, &body.local_decls, slice_len_fn_item_def_id);
+        lower_slice_len_call(block, slice_len_fn_item_def_id);
     }
 }
 
-fn lower_slice_len_call<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    block: &mut BasicBlockData<'tcx>,
-    local_decls: &IndexSlice<Local, LocalDecl<'tcx>>,
-    slice_len_fn_item_def_id: DefId,
-) {
+fn lower_slice_len_call<'tcx>(block: &mut BasicBlockData<'tcx>, slice_len_fn_item_def_id: DefId) {
     let terminator = block.terminator();
     if let TerminatorKind::Call {
         func,
@@ -50,19 +44,17 @@ fn lower_slice_len_call<'tcx>(
     } = &terminator.kind
         // some heuristics for fast rejection
         && let [arg] = &args[..]
-        && let Some(arg) = arg.node.place()
-        && let ty::FnDef(fn_def_id, _) = func.ty(local_decls, tcx).kind()
-        && *fn_def_id == slice_len_fn_item_def_id
+        && let Some((fn_def_id, _)) = func.const_fn_def()
+        && fn_def_id == slice_len_fn_item_def_id
     {
         // perform modifications from something like:
         //     _5 = core::slice::<impl [u8]>::len(move _6) -> bb1
         // into:
-        //     _5 = Len(*_6)
+        //     _5 = PtrMetadata(move _6)
         //     goto bb1
 
         // make new RValue for Len
-        let deref_arg = tcx.mk_place_deref(arg);
-        let r_value = Rvalue::Len(deref_arg);
+        let r_value = Rvalue::UnaryOp(UnOp::PtrMetadata, arg.node.clone());
         let len_statement_kind = StatementKind::Assign(Box::new((*destination, r_value)));
         let add_statement =
             Statement { kind: len_statement_kind, source_info: terminator.source_info };

compiler/rustc_mir_transform/src/normalize_array_len.rs

@@ -1,6 +1,5 @@
 // skip-filecheck
 // EMIT_MIR_FOR_EACH_PANIC_STRATEGY
-//@ compile-flags: -Zmir-enable-passes=-NormalizeArrayLen
 // Check that we do not insert StorageDead at each target if StorageDead was never seen
 
 use std::fmt::Debug;

tests/mir-opt/issue_76432.rs

@@ -1,5 +1,5 @@
-- // MIR for `array_bound` before NormalizeArrayLen
-+ // MIR for `array_bound` after NormalizeArrayLen
+- // MIR for `array_bound` before GVN
++ // MIR for `array_bound` after GVN
 
   fn array_bound(_1: usize, _2: &[u8; N]) -> u8 {
       debug index => _1;
@@ -24,14 +24,15 @@
           _7 = &(*_2);
           _6 = move _7 as &[u8] (PointerCoercion(Unsize));
           StorageDead(_7);
--         _5 = Len((*_6));
+-         _5 = PtrMetadata(move _6);
 +         _5 = const N;
           goto -> bb1;
       }
 
       bb1: {
           StorageDead(_6);
-          _3 = Lt(move _4, move _5);
+-         _3 = Lt(move _4, move _5);
++         _3 = Lt(_1, move _5);
           switchInt(move _3) -> [0: bb4, otherwise: bb2];
       }
 
@@ -40,13 +41,17 @@
           StorageDead(_4);
           StorageLive(_8);
           _8 = _1;
-          _9 = Len((*_2));
-          _10 = Lt(_8, _9);
-          assert(move _10, "index out of bounds: the length is {} but the index is {}", move _9, _8) -> [success: bb3, unwind unreachable];
+-         _9 = Len((*_2));
+-         _10 = Lt(_8, _9);
+-         assert(move _10, "index out of bounds: the length is {} but the index is {}", move _9, _8) -> [success: bb3, unwind unreachable];
++         _9 = const N;
++         _10 = Lt(_1, const N);
++         assert(move _10, "index out of bounds: the length is {} but the index is {}", const N, _1) -> [success: bb3, unwind unreachable];
       }
 
       bb3: {
-          _0 = (*_2)[_8];
+-         _0 = (*_2)[_8];
++         _0 = (*_2)[_1];
           StorageDead(_8);
           goto -> bb5;
       }

tests/mir-opt/lower_array_len.array_bound.NormalizeArrayLen.panic-abort.diff renamed to tests/mir-opt/lower_array_len.array_bound.GVN.panic-abort.diff

@@ -1,5 +1,5 @@
-- // MIR for `array_bound` before NormalizeArrayLen
-+ // MIR for `array_bound` after NormalizeArrayLen
+- // MIR for `array_bound` before GVN
++ // MIR for `array_bound` after GVN
 
   fn array_bound(_1: usize, _2: &[u8; N]) -> u8 {
       debug index => _1;
@@ -24,14 +24,15 @@
           _7 = &(*_2);
           _6 = move _7 as &[u8] (PointerCoercion(Unsize));
           StorageDead(_7);
--         _5 = Len((*_6));
+-         _5 = PtrMetadata(move _6);
 +         _5 = const N;
           goto -> bb1;
       }
 
       bb1: {
           StorageDead(_6);
-          _3 = Lt(move _4, move _5);
+-         _3 = Lt(move _4, move _5);
++         _3 = Lt(_1, move _5);
           switchInt(move _3) -> [0: bb4, otherwise: bb2];
       }
 
@@ -40,13 +41,17 @@
           StorageDead(_4);
           StorageLive(_8);
           _8 = _1;
-          _9 = Len((*_2));
-          _10 = Lt(_8, _9);
-          assert(move _10, "index out of bounds: the length is {} but the index is {}", move _9, _8) -> [success: bb3, unwind continue];
+-         _9 = Len((*_2));
+-         _10 = Lt(_8, _9);
+-         assert(move _10, "index out of bounds: the length is {} but the index is {}", move _9, _8) -> [success: bb3, unwind continue];
++         _9 = const N;
++         _10 = Lt(_1, const N);
++         assert(move _10, "index out of bounds: the length is {} but the index is {}", const N, _1) -> [success: bb3, unwind continue];
       }
 
       bb3: {
-          _0 = (*_2)[_8];
+-         _0 = (*_2)[_8];
++         _0 = (*_2)[_1];
           StorageDead(_8);
           goto -> bb5;
       }

tests/mir-opt/lower_array_len.array_bound.NormalizeArrayLen.panic-unwind.diff renamed to tests/mir-opt/lower_array_len.array_bound.GVN.panic-unwind.diff

@@ -1,5 +1,5 @@
-- // MIR for `array_bound_mut` before NormalizeArrayLen
-+ // MIR for `array_bound_mut` after NormalizeArrayLen
+- // MIR for `array_bound_mut` before GVN
++ // MIR for `array_bound_mut` after GVN
 
   fn array_bound_mut(_1: usize, _2: &mut [u8; N]) -> u8 {
       debug index => _1;
@@ -27,14 +27,15 @@
           _7 = &(*_2);
           _6 = move _7 as &[u8] (PointerCoercion(Unsize));
           StorageDead(_7);
--         _5 = Len((*_6));
+-         _5 = PtrMetadata(move _6);
 +         _5 = const N;
           goto -> bb1;
       }
 
       bb1: {
           StorageDead(_6);
-          _3 = Lt(move _4, move _5);
+-         _3 = Lt(move _4, move _5);
++         _3 = Lt(_1, move _5);
           switchInt(move _3) -> [0: bb4, otherwise: bb2];
       }
 
@@ -43,13 +44,17 @@
           StorageDead(_4);
           StorageLive(_8);
           _8 = _1;
-          _9 = Len((*_2));
-          _10 = Lt(_8, _9);
-          assert(move _10, "index out of bounds: the length is {} but the index is {}", move _9, _8) -> [success: bb3, unwind unreachable];
+-         _9 = Len((*_2));
+-         _10 = Lt(_8, _9);
+-         assert(move _10, "index out of bounds: the length is {} but the index is {}", move _9, _8) -> [success: bb3, unwind unreachable];
++         _9 = const N;
++         _10 = Lt(_1, const N);
++         assert(move _10, "index out of bounds: the length is {} but the index is {}", const N, _1) -> [success: bb3, unwind unreachable];
       }
 
       bb3: {
-          _0 = (*_2)[_8];
+-         _0 = (*_2)[_8];
++         _0 = (*_2)[_1];
           StorageDead(_8);
           goto -> bb6;
       }
@@ -59,13 +64,17 @@
           StorageDead(_4);
           StorageLive(_11);
           _11 = const 0_usize;
-          _12 = Len((*_2));
-          _13 = Lt(_11, _12);
-          assert(move _13, "index out of bounds: the length is {} but the index is {}", move _12, _11) -> [success: bb5, unwind unreachable];
+-         _12 = Len((*_2));
+-         _13 = Lt(_11, _12);
+-         assert(move _13, "index out of bounds: the length is {} but the index is {}", move _12, _11) -> [success: bb5, unwind unreachable];
++         _12 = const N;
++         _13 = Lt(const 0_usize, const N);
++         assert(move _13, "index out of bounds: the length is {} but the index is {}", const N, const 0_usize) -> [success: bb5, unwind unreachable];
       }
 
       bb5: {
-          (*_2)[_11] = const 42_u8;
+-         (*_2)[_11] = const 42_u8;
++         (*_2)[0 of 1] = const 42_u8;
           StorageDead(_11);
           _0 = const 42_u8;
           goto -> bb6;