Auto merge of #110822 - scottmcm:lower-offset-to-mir, r=compiler-errors

Lower `intrinsics::offset` to `mir::BinOp::Offset`

They're [semantically the same](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/mir/enum.Rvalue.html#variant.BinaryOp), so this means the backends don't need to handle the intrinsic and means fewer MIR basic blocks in pointer arithmetic code.

2 files changed, 35 insertions, 0 deletions

diff --git a/tests/mir-opt/lower_intrinsics.ptr_offset.LowerIntrinsics.diff b/tests/mir-opt/lower_intrinsics.ptr_offset.LowerIntrinsics.diff
new file mode 100644
index 00000000000..f342bf30d02
--- /dev/null
+++ b/tests/mir-opt/lower_intrinsics.ptr_offset.LowerIntrinsics.diff
@@ -0,0 +1,30 @@
+- // MIR for `ptr_offset` before LowerIntrinsics
++ // MIR for `ptr_offset` after LowerIntrinsics
+  
+  fn ptr_offset(_1: *const i32, _2: isize) -> *const i32 {
+      debug p => _1;                       // in scope 0 at $DIR/lower_intrinsics.rs:+0:26: +0:27
+      debug d => _2;                       // in scope 0 at $DIR/lower_intrinsics.rs:+0:41: +0:42
+      let mut _0: *const i32;              // return place in scope 0 at $DIR/lower_intrinsics.rs:+0:54: +0:64
+      let mut _3: *const i32;              // in scope 0 at $DIR/lower_intrinsics.rs:+1:30: +1:31
+      let mut _4: isize;                   // in scope 0 at $DIR/lower_intrinsics.rs:+1:33: +1:34
+  
+      bb0: {
+          StorageLive(_3);                 // scope 0 at $DIR/lower_intrinsics.rs:+1:30: +1:31
+          _3 = _1;                         // scope 0 at $DIR/lower_intrinsics.rs:+1:30: +1:31
+          StorageLive(_4);                 // scope 0 at $DIR/lower_intrinsics.rs:+1:33: +1:34
+          _4 = _2;                         // scope 0 at $DIR/lower_intrinsics.rs:+1:33: +1:34
+-         _0 = offset::<i32>(move _3, move _4) -> [return: bb1, unwind unreachable]; // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:35
+-                                          // mir::Constant
+-                                          // + span: $DIR/lower_intrinsics.rs:140:5: 140:29
+-                                          // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(*const i32, isize) -> *const i32 {offset::<i32>}, val: Value(<ZST>) }
++         _0 = Offset(move _3, move _4);   // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:35
++         goto -> bb1;                     // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:35
+      }
+  
+      bb1: {
+          StorageDead(_4);                 // scope 0 at $DIR/lower_intrinsics.rs:+1:34: +1:35
+          StorageDead(_3);                 // scope 0 at $DIR/lower_intrinsics.rs:+1:34: +1:35
+          return;                          // scope 0 at $DIR/lower_intrinsics.rs:+2:2: +2:2
+      }
+  }
+  
diff --git a/tests/mir-opt/lower_intrinsics.rs b/tests/mir-opt/lower_intrinsics.rs
index 33fef930ad3..ad690f803c4 100644
--- a/tests/mir-opt/lower_intrinsics.rs
+++ b/tests/mir-opt/lower_intrinsics.rs
@@ -134,3 +134,8 @@ pub fn option_payload(o: &Option<usize>, p: &Option<String>) {
         let _y = core::intrinsics::option_payload_ptr(p);
     }
 }
+
+// EMIT_MIR lower_intrinsics.ptr_offset.LowerIntrinsics.diff
+pub unsafe fn ptr_offset(p: *const i32, d: isize) -> *const i32 {
+    core::intrinsics::offset(p, d)
+}