Auto merge of #122582 - scottmcm:swap-intrinsic-v2, r=oli-obk

Let codegen decide when to `mem::swap` with immediates

Making `libcore` decide this is silly; the backend has so much better information about when it's a good idea.

Thus this PR introduces a new `typed_swap` intrinsic with a fallback body, and replaces that fallback implementation when swapping immediates or scalar pairs.

r? oli-obk

Replaces #111744, and means we'll never need more libs PRs like #111803 or #107140

1 files changed, 23 insertions, 2 deletions

diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
index a84ef4ce08e..a8478f721c7 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -21,8 +21,8 @@ use rustc_span::symbol::{sym, Symbol};
 use rustc_target::abi::Size;
 
 use super::{
-    util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx, MPlaceTy, Machine, OpTy,
-    Pointer,
+    memory::MemoryKind, util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx,
+    MPlaceTy, Machine, OpTy, Pointer,
 };
 
 use crate::fluent_generated as fluent;
@@ -414,6 +414,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let result = self.raw_eq_intrinsic(&args[0], &args[1])?;
                 self.write_scalar(result, dest)?;
             }
+            sym::typed_swap => {
+                self.typed_swap_intrinsic(&args[0], &args[1])?;
+            }
 
             sym::vtable_size => {
                 let ptr = self.read_pointer(&args[0])?;
@@ -607,6 +610,24 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         self.mem_copy(src, dst, size, nonoverlapping)
     }
 
+    /// Does a *typed* swap of `*left` and `*right`.
+    fn typed_swap_intrinsic(
+        &mut self,
+        left: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
+        right: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,
+    ) -> InterpResult<'tcx> {
+        let left = self.deref_pointer(left)?;
+        let right = self.deref_pointer(right)?;
+        debug_assert_eq!(left.layout, right.layout);
+        let kind = MemoryKind::Stack;
+        let temp = self.allocate(left.layout, kind)?;
+        self.copy_op(&left, &temp)?;
+        self.copy_op(&right, &left)?;
+        self.copy_op(&temp, &right)?;
+        self.deallocate_ptr(temp.ptr(), None, kind)?;
+        Ok(())
+    }
+
     pub(crate) fn write_bytes_intrinsic(
         &mut self,
         dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::Provenance>,