Add test ensuring that we don't propagate large arrays

src/test/mir-opt/const_prop/large_array_index.rs

+// EMIT_MIR_FOR_EACH_BIT_WIDTH
+
+// EMIT_MIR rustc.main.ConstProp.diff
+fn main() {
+    // check that we don't propagate this, because it's too large
+    let x: u8 = [0_u8; 5000][2];
+}

src/test/mir-opt/const_prop/large_array_index/32bit/rustc.main.ConstProp.diff

+- // MIR for `main` before ConstProp
++ // MIR for `main` after ConstProp
+  
+  fn main() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/large_array_index.rs:4:11: 4:11
+      let _1: u8;                          // in scope 0 at $DIR/large_array_index.rs:6:9: 6:10
+      let mut _2: [u8; 5000];              // in scope 0 at $DIR/large_array_index.rs:6:17: 6:29
+      let _3: usize;                       // in scope 0 at $DIR/large_array_index.rs:6:30: 6:31
+      let mut _4: usize;                   // in scope 0 at $DIR/large_array_index.rs:6:17: 6:32
+      let mut _5: bool;                    // in scope 0 at $DIR/large_array_index.rs:6:17: 6:32
+      scope 1 {
+          debug x => _1;                   // in scope 1 at $DIR/large_array_index.rs:6:9: 6:10
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 0 at $DIR/large_array_index.rs:6:9: 6:10
+          StorageLive(_2);                 // scope 0 at $DIR/large_array_index.rs:6:17: 6:29
+          _2 = [const 0_u8; 5000];         // scope 0 at $DIR/large_array_index.rs:6:17: 6:29
+                                           // ty::Const
+                                           // + ty: u8
+                                           // + val: Value(Scalar(0x00))
+                                           // mir::Constant
+                                           // + span: $DIR/large_array_index.rs:6:18: 6:22
+                                           // + literal: Const { ty: u8, val: Value(Scalar(0x00)) }
+          StorageLive(_3);                 // scope 0 at $DIR/large_array_index.rs:6:30: 6:31
+          _3 = const 2_usize;              // scope 0 at $DIR/large_array_index.rs:6:30: 6:31
+                                           // ty::Const
+                                           // + ty: usize
+                                           // + val: Value(Scalar(0x00000002))
+                                           // mir::Constant
+                                           // + span: $DIR/large_array_index.rs:6:30: 6:31
+                                           // + literal: Const { ty: usize, val: Value(Scalar(0x00000002)) }
+          _4 = const 5000_usize;           // scope 0 at $DIR/large_array_index.rs:6:17: 6:32
+                                           // ty::Const
+                                           // + ty: usize
+                                           // + val: Value(Scalar(0x00001388))
+                                           // mir::Constant
+                                           // + span: $DIR/large_array_index.rs:6:17: 6:32
+                                           // + literal: Const { ty: usize, val: Value(Scalar(0x00001388)) }
+-         _5 = Lt(_3, _4);                 // scope 0 at $DIR/large_array_index.rs:6:17: 6:32
+-         assert(move _5, "index out of bounds: the len is {} but the index is {}", move _4, _3) -> bb1; // scope 0 at $DIR/large_array_index.rs:6:17: 6:32
++         _5 = const true;                 // scope 0 at $DIR/large_array_index.rs:6:17: 6:32
++                                          // ty::Const
++                                          // + ty: bool
++                                          // + val: Value(Scalar(0x01))
++                                          // mir::Constant
++                                          // + span: $DIR/large_array_index.rs:6:17: 6:32
++                                          // + literal: Const { ty: bool, val: Value(Scalar(0x01)) }
++         assert(const true, "index out of bounds: the len is {} but the index is {}", const 5000_usize, const 2_usize) -> bb1; // scope 0 at $DIR/large_array_index.rs:6:17: 6:32
++                                          // ty::Const
++                                          // + ty: bool
++                                          // + val: Value(Scalar(0x01))
++                                          // mir::Constant
++                                          // + span: $DIR/large_array_index.rs:6:17: 6:32
++                                          // + literal: Const { ty: bool, val: Value(Scalar(0x01)) }
++                                          // ty::Const
++                                          // + ty: usize
++                                          // + val: Value(Scalar(0x00001388))
++                                          // mir::Constant
++                                          // + span: $DIR/large_array_index.rs:6:17: 6:32
++                                          // + literal: Const { ty: usize, val: Value(Scalar(0x00001388)) }
++                                          // ty::Const
++                                          // + ty: usize
++                                          // + val: Value(Scalar(0x00000002))
++                                          // mir::Constant
++                                          // + span: $DIR/large_array_index.rs:6:17: 6:32
++                                          // + literal: Const { ty: usize, val: Value(Scalar(0x00000002)) }
+      }
+  
+      bb1: {
+          _1 = _2[_3];                     // scope 0 at $DIR/large_array_index.rs:6:17: 6:32
+          StorageDead(_3);                 // scope 0 at $DIR/large_array_index.rs:6:32: 6:33
+          StorageDead(_2);                 // scope 0 at $DIR/large_array_index.rs:6:32: 6:33
+          _0 = const ();                   // scope 0 at $DIR/large_array_index.rs:4:11: 7:2
+                                           // ty::Const
+                                           // + ty: ()
+                                           // + val: Value(Scalar(<ZST>))
+                                           // mir::Constant
+                                           // + span: $DIR/large_array_index.rs:4:11: 7:2
+                                           // + literal: Const { ty: (), val: Value(Scalar(<ZST>)) }
+          StorageDead(_1);                 // scope 0 at $DIR/large_array_index.rs:7:1: 7:2
+          return;                          // scope 0 at $DIR/large_array_index.rs:7:2: 7:2
+      }
+  }
+  

src/test/mir-opt/const_prop/large_array_index/64bit/rustc.main.ConstProp.diff

+- // MIR for `main` before ConstProp
++ // MIR for `main` after ConstProp
+  
+  fn main() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/large_array_index.rs:4:11: 4:11
+      let _1: u8;                          // in scope 0 at $DIR/large_array_index.rs:6:9: 6:10
+      let mut _2: [u8; 5000];              // in scope 0 at $DIR/large_array_index.rs:6:17: 6:29
+      let _3: usize;                       // in scope 0 at $DIR/large_array_index.rs:6:30: 6:31
+      let mut _4: usize;                   // in scope 0 at $DIR/large_array_index.rs:6:17: 6:32
+      let mut _5: bool;                    // in scope 0 at $DIR/large_array_index.rs:6:17: 6:32
+      scope 1 {
+          debug x => _1;                   // in scope 1 at $DIR/large_array_index.rs:6:9: 6:10
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 0 at $DIR/large_array_index.rs:6:9: 6:10
+          StorageLive(_2);                 // scope 0 at $DIR/large_array_index.rs:6:17: 6:29
+          _2 = [const 0_u8; 5000];         // scope 0 at $DIR/large_array_index.rs:6:17: 6:29
+                                           // ty::Const
+                                           // + ty: u8
+                                           // + val: Value(Scalar(0x00))
+                                           // mir::Constant
+                                           // + span: $DIR/large_array_index.rs:6:18: 6:22
+                                           // + literal: Const { ty: u8, val: Value(Scalar(0x00)) }
+          StorageLive(_3);                 // scope 0 at $DIR/large_array_index.rs:6:30: 6:31
+          _3 = const 2_usize;              // scope 0 at $DIR/large_array_index.rs:6:30: 6:31
+                                           // ty::Const
+                                           // + ty: usize
+                                           // + val: Value(Scalar(0x0000000000000002))
+                                           // mir::Constant
+                                           // + span: $DIR/large_array_index.rs:6:30: 6:31
+                                           // + literal: Const { ty: usize, val: Value(Scalar(0x0000000000000002)) }
+          _4 = const 5000_usize;           // scope 0 at $DIR/large_array_index.rs:6:17: 6:32
+                                           // ty::Const
+                                           // + ty: usize
+                                           // + val: Value(Scalar(0x0000000000001388))
+                                           // mir::Constant
+                                           // + span: $DIR/large_array_index.rs:6:17: 6:32
+                                           // + literal: Const { ty: usize, val: Value(Scalar(0x0000000000001388)) }
+-         _5 = Lt(_3, _4);                 // scope 0 at $DIR/large_array_index.rs:6:17: 6:32
+-         assert(move _5, "index out of bounds: the len is {} but the index is {}", move _4, _3) -> bb1; // scope 0 at $DIR/large_array_index.rs:6:17: 6:32
++         _5 = const true;                 // scope 0 at $DIR/large_array_index.rs:6:17: 6:32
++                                          // ty::Const
++                                          // + ty: bool
++                                          // + val: Value(Scalar(0x01))
++                                          // mir::Constant
++                                          // + span: $DIR/large_array_index.rs:6:17: 6:32
++                                          // + literal: Const { ty: bool, val: Value(Scalar(0x01)) }
++         assert(const true, "index out of bounds: the len is {} but the index is {}", const 5000_usize, const 2_usize) -> bb1; // scope 0 at $DIR/large_array_index.rs:6:17: 6:32
++                                          // ty::Const
++                                          // + ty: bool
++                                          // + val: Value(Scalar(0x01))
++                                          // mir::Constant
++                                          // + span: $DIR/large_array_index.rs:6:17: 6:32
++                                          // + literal: Const { ty: bool, val: Value(Scalar(0x01)) }
++                                          // ty::Const
++                                          // + ty: usize
++                                          // + val: Value(Scalar(0x0000000000001388))
++                                          // mir::Constant
++                                          // + span: $DIR/large_array_index.rs:6:17: 6:32
++                                          // + literal: Const { ty: usize, val: Value(Scalar(0x0000000000001388)) }
++                                          // ty::Const
++                                          // + ty: usize
++                                          // + val: Value(Scalar(0x0000000000000002))
++                                          // mir::Constant
++                                          // + span: $DIR/large_array_index.rs:6:17: 6:32
++                                          // + literal: Const { ty: usize, val: Value(Scalar(0x0000000000000002)) }
+      }
+  
+      bb1: {
+          _1 = _2[_3];                     // scope 0 at $DIR/large_array_index.rs:6:17: 6:32
+          StorageDead(_3);                 // scope 0 at $DIR/large_array_index.rs:6:32: 6:33
+          StorageDead(_2);                 // scope 0 at $DIR/large_array_index.rs:6:32: 6:33
+          _0 = const ();                   // scope 0 at $DIR/large_array_index.rs:4:11: 7:2
+                                           // ty::Const
+                                           // + ty: ()
+                                           // + val: Value(Scalar(<ZST>))
+                                           // mir::Constant
+                                           // + span: $DIR/large_array_index.rs:4:11: 7:2
+                                           // + literal: Const { ty: (), val: Value(Scalar(<ZST>)) }
+          StorageDead(_1);                 // scope 0 at $DIR/large_array_index.rs:7:1: 7:2
+          return;                          // scope 0 at $DIR/large_array_index.rs:7:2: 7:2
+      }
+  }
+