Always run intrinsics lowering pass

Move intrinsics lowering pass from the optimization phase (where it
would not run if -Zmir-opt-level=0), to the drop lowering phase where it
runs unconditionally.

The implementation of those intrinsics in code generation and
interpreter is unnecessary. Remove it.

Author: tmiasko

compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

@@ -83,9 +83,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 return;
             }
 
-            sym::unreachable => {
-                return;
-            }
             sym::va_start => bx.va_start(args[0].immediate()),
             sym::va_end => bx.va_end(args[0].immediate()),
             sym::size_of_val => {
@@ -106,8 +103,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     bx.const_usize(bx.layout_of(tp_ty).align.abi.bytes())
                 }
             }
-            sym::size_of
-            | sym::pref_align_of
+            sym::pref_align_of
             | sym::min_align_of
             | sym::needs_drop
             | sym::type_id
@@ -119,10 +115,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     .unwrap();
                 OperandRef::from_const(bx, value, ret_ty).immediate_or_packed_pair(bx)
             }
-            // Effectively no-op
-            sym::forget => {
-                return;
-            }
             sym::offset => {
                 let ptr = args[0].immediate();
                 let offset = args[1].immediate();
@@ -218,9 +210,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             sym::add_with_overflow
             | sym::sub_with_overflow
             | sym::mul_with_overflow
-            | sym::wrapping_add
-            | sym::wrapping_sub
-            | sym::wrapping_mul
             | sym::unchecked_div
             | sym::unchecked_rem
             | sym::unchecked_shl
@@ -254,9 +243,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
                             return;
                         }
-                        sym::wrapping_add => bx.add(args[0].immediate(), args[1].immediate()),
-                        sym::wrapping_sub => bx.sub(args[0].immediate(), args[1].immediate()),
-                        sym::wrapping_mul => bx.mul(args[0].immediate(), args[1].immediate()),
                         sym::exact_div => {
                             if signed {
                                 bx.exactsdiv(args[0].immediate(), args[1].immediate())

compiler/rustc_mir/src/interpret/intrinsics.rs

@@ -61,12 +61,11 @@ crate fn eval_nullary_intrinsic<'tcx>(
             ConstValue::Slice { data: alloc, start: 0, end: alloc.len() }
         }
         sym::needs_drop => ConstValue::from_bool(tp_ty.needs_drop(tcx, param_env)),
-        sym::size_of | sym::min_align_of | sym::pref_align_of => {
+        sym::min_align_of | sym::pref_align_of => {
             let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
             let n = match name {
                 sym::pref_align_of => layout.align.pref.bytes(),
                 sym::min_align_of => layout.align.abi.bytes(),
-                sym::size_of => layout.size.bytes(),
                 _ => bug!(),
             };
             ConstValue::from_machine_usize(n, &tcx)
@@ -125,7 +124,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         let (dest, ret) = match ret {
             None => match intrinsic_name {
                 sym::transmute => throw_ub_format!("transmuting to uninhabited type"),
-                sym::unreachable => throw_ub!(Unreachable),
                 sym::abort => M::abort(self, "the program aborted execution".to_owned())?,
                 // Unsupported diverging intrinsic.
                 _ => return Ok(false),
@@ -160,13 +158,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             sym::min_align_of
             | sym::pref_align_of
             | sym::needs_drop
-            | sym::size_of
             | sym::type_id
             | sym::type_name
             | sym::variant_count => {
                 let gid = GlobalId { instance, promoted: None };
                 let ty = match intrinsic_name {
-                    sym::min_align_of | sym::pref_align_of | sym::size_of | sym::variant_count => {
+                    sym::min_align_of | sym::pref_align_of | sym::variant_count => {
                         self.tcx.types.usize
                     }
                     sym::needs_drop => self.tcx.types.bool,
@@ -212,28 +209,16 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let out_val = numeric_intrinsic(intrinsic_name, bits, kind)?;
                 self.write_scalar(out_val, dest)?;
             }
-            sym::wrapping_add
-            | sym::wrapping_sub
-            | sym::wrapping_mul
-            | sym::add_with_overflow
-            | sym::sub_with_overflow
-            | sym::mul_with_overflow => {
+            sym::add_with_overflow | sym::sub_with_overflow | sym::mul_with_overflow => {
                 let lhs = self.read_immediate(args[0])?;
                 let rhs = self.read_immediate(args[1])?;
-                let (bin_op, ignore_overflow) = match intrinsic_name {
-                    sym::wrapping_add => (BinOp::Add, true),
-                    sym::wrapping_sub => (BinOp::Sub, true),
-                    sym::wrapping_mul => (BinOp::Mul, true),
-                    sym::add_with_overflow => (BinOp::Add, false),
-                    sym::sub_with_overflow => (BinOp::Sub, false),
-                    sym::mul_with_overflow => (BinOp::Mul, false),
+                let bin_op = match intrinsic_name {
+                    sym::add_with_overflow => BinOp::Add,
+                    sym::sub_with_overflow => BinOp::Sub,
+                    sym::mul_with_overflow => BinOp::Mul,
                     _ => bug!("Already checked for int ops"),
                 };
-                if ignore_overflow {
-                    self.binop_ignore_overflow(bin_op, lhs, rhs, dest)?;
-                } else {
-                    self.binop_with_overflow(bin_op, lhs, rhs, dest)?;
-                }
+                self.binop_with_overflow(bin_op, lhs, rhs, dest)?;
             }
             sym::saturating_add | sym::saturating_sub => {
                 let l = self.read_immediate(args[0])?;

compiler/rustc_mir/src/transform/mod.rs

@@ -363,6 +363,7 @@ fn run_post_borrowck_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tc
         // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
         // but before optimizations begin.
         &add_retag::AddRetag,
+        &lower_intrinsics::LowerIntrinsics,
         &simplify::SimplifyCfg::new("elaborate-drops"),
         // `Deaggregator` is conceptually part of MIR building, some backends rely on it happening
         // and it can help optimizations.
@@ -391,7 +392,6 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 
     // The main optimizations that we do on MIR.
     let optimizations: &[&dyn MirPass<'tcx>] = &[
-        &lower_intrinsics::LowerIntrinsics,
         &remove_unneeded_drops::RemoveUnneededDrops,
         &match_branches::MatchBranchSimplification,
         // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)

src/test/mir-opt/lower_intrinsics.forget.LowerIntrinsics.diff

@@ -25,7 +25,15 @@
           StorageDead(_3);                 // scope 1 at $DIR/lower_intrinsics.rs:19:40: 19:41
           StorageDead(_2);                 // scope 0 at $DIR/lower_intrinsics.rs:19:43: 19:44
           _0 = const ();                   // scope 0 at $DIR/lower_intrinsics.rs:18:24: 20:2
+          goto -> bb2;                     // scope 0 at $DIR/lower_intrinsics.rs:20:1: 20:2
+      }
+  
+      bb2: {
           return;                          // scope 0 at $DIR/lower_intrinsics.rs:20:2: 20:2
       }
+  
+      bb3 (cleanup): {
+          resume;                          // scope 0 at $DIR/lower_intrinsics.rs:18:1: 20:2
+      }
   }
 

src/test/mir-opt/lower_intrinsics.non_const.LowerIntrinsics.diff

@@ -27,5 +27,9 @@
           StorageDead(_1);                 // scope 0 at $DIR/lower_intrinsics.rs:59:1: 59:2
           return;                          // scope 0 at $DIR/lower_intrinsics.rs:59:2: 59:2
       }
+  
+      bb2 (cleanup): {
+          resume;                          // scope 0 at $DIR/lower_intrinsics.rs:55:1: 59:2
+      }
   }
 

src/test/mir-opt/lower_intrinsics.size_of.LowerIntrinsics.diff

@@ -16,5 +16,9 @@
       bb1: {
           return;                          // scope 0 at $DIR/lower_intrinsics.rs:15:2: 15:2
       }
+  
+      bb2 (cleanup): {
+          resume;                          // scope 0 at $DIR/lower_intrinsics.rs:13:1: 15:2
+      }
   }
 

src/test/mir-opt/lower_intrinsics.unreachable.LowerIntrinsics.diff

@@ -18,5 +18,9 @@
 -                                          // + literal: Const { ty: unsafe extern "rust-intrinsic" fn() -> ! {std::intrinsics::unreachable}, val: Value(Scalar(<ZST>)) }
 +         unreachable;                     // scope 1 at $DIR/lower_intrinsics.rs:24:14: 24:45
       }
+  
+      bb1 (cleanup): {
+          resume;                          // scope 0 at $DIR/lower_intrinsics.rs:23:1: 25:2
+      }
   }
 

src/test/mir-opt/lower_intrinsics.wrapping.LowerIntrinsics.diff

@@ -79,5 +79,9 @@
           StorageDead(_3);                 // scope 0 at $DIR/lower_intrinsics.rs:10:1: 10:2
           return;                          // scope 0 at $DIR/lower_intrinsics.rs:10:2: 10:2
       }
+  
+      bb4 (cleanup): {
+          resume;                          // scope 0 at $DIR/lower_intrinsics.rs:6:1: 10:2
+      }
   }