Auto merge of rust-lang#3462 - eduardosm:chunk-128, r=RalfJung

Make `split_simd_to_128bit_chunks` take only one operand

It will allow more flexible uses in the future. This makes `split_simd_to_128bit_chunks` simpler, moving some of the complexity to its callers.

src/tools/miri/src/shims/x86/mod.rs

@@ -664,54 +664,35 @@ fn convert_float_to_int<'tcx>(
     Ok(())
 }
 
-/// Splits `left`, `right` and `dest` (which must be SIMD vectors)
-/// into 128-bit chuncks.
-///
-/// `left`, `right` and `dest` cannot have different types.
+/// Splits `op` (which must be a SIMD vector) into 128-bit chuncks.
 ///
 /// Returns a tuple where:
 /// * The first element is the number of 128-bit chunks (let's call it `N`).
 /// * The second element is the number of elements per chunk (let's call it `M`).
-/// * The third element is the `left` vector split into chunks, i.e, it's
-///   type is `[[T; M]; N]`.
-/// * The fourth element is the `right` vector split into chunks.
-/// * The fifth element is the `dest` vector split into chunks.
-fn split_simd_to_128bit_chunks<'tcx>(
+/// * The third element is the `op` vector split into chunks, i.e, it's
+///   type is `[[T; M]; N]` where `T` is the element type of `op`.
+fn split_simd_to_128bit_chunks<'tcx, P: Projectable<'tcx, Provenance>>(
     this: &mut crate::MiriInterpCx<'_, 'tcx>,
-    left: &OpTy<'tcx, Provenance>,
-    right: &OpTy<'tcx, Provenance>,
-    dest: &MPlaceTy<'tcx, Provenance>,
-) -> InterpResult<
-    'tcx,
-    (u64, u64, MPlaceTy<'tcx, Provenance>, MPlaceTy<'tcx, Provenance>, MPlaceTy<'tcx, Provenance>),
-> {
-    assert_eq!(dest.layout, left.layout);
-    assert_eq!(dest.layout, right.layout);
+    op: &P,
+) -> InterpResult<'tcx, (u64, u64, P)> {
+    let simd_layout = op.layout();
+    let (simd_len, element_ty) = simd_layout.ty.simd_size_and_type(this.tcx.tcx);
 
-    let (left, left_len) = this.operand_to_simd(left)?;
-    let (right, right_len) = this.operand_to_simd(right)?;
-    let (dest, dest_len) = this.mplace_to_simd(dest)?;
-
-    assert_eq!(dest_len, left_len);
-    assert_eq!(dest_len, right_len);
-
-    assert_eq!(dest.layout.size.bits() % 128, 0);
-    let num_chunks = dest.layout.size.bits() / 128;
-    assert_eq!(dest_len.checked_rem(num_chunks), Some(0));
-    let items_per_chunk = dest_len.checked_div(num_chunks).unwrap();
+    assert_eq!(simd_layout.size.bits() % 128, 0);
+    let num_chunks = simd_layout.size.bits() / 128;
+    let items_per_chunk = simd_len.checked_div(num_chunks).unwrap();
 
     // Transmute to `[[T; items_per_chunk]; num_chunks]`
-    let element_layout = left.layout.field(this, 0);
-    let chunked_layout = this.layout_of(Ty::new_array(
-        this.tcx.tcx,
-        Ty::new_array(this.tcx.tcx, element_layout.ty, items_per_chunk),
-        num_chunks,
-    ))?;
-    let left = left.transmute(chunked_layout, this)?;
-    let right = right.transmute(chunked_layout, this)?;
-    let dest = dest.transmute(chunked_layout, this)?;
-
-    Ok((num_chunks, items_per_chunk, left, right, dest))
+    let chunked_layout = this
+        .layout_of(Ty::new_array(
+            this.tcx.tcx,
+            Ty::new_array(this.tcx.tcx, element_ty, items_per_chunk),
+            num_chunks,
+        ))
+        .unwrap();
+    let chunked_op = op.transmute(chunked_layout, this)?;
+
+    Ok((num_chunks, items_per_chunk, chunked_op))
 }
 
 /// Horizontaly performs `which` operation on adjacent values of
@@ -731,8 +712,12 @@ fn horizontal_bin_op<'tcx>(
     right: &OpTy<'tcx, Provenance>,
     dest: &MPlaceTy<'tcx, Provenance>,
 ) -> InterpResult<'tcx, ()> {
-    let (num_chunks, items_per_chunk, left, right, dest) =
-        split_simd_to_128bit_chunks(this, left, right, dest)?;
+    assert_eq!(left.layout, dest.layout);
+    assert_eq!(right.layout, dest.layout);
+
+    let (num_chunks, items_per_chunk, left) = split_simd_to_128bit_chunks(this, left)?;
+    let (_, _, right) = split_simd_to_128bit_chunks(this, right)?;
+    let (_, _, dest) = split_simd_to_128bit_chunks(this, dest)?;
 
     let middle = items_per_chunk / 2;
     for i in 0..num_chunks {
@@ -779,8 +764,12 @@ fn conditional_dot_product<'tcx>(
     imm: &OpTy<'tcx, Provenance>,
     dest: &MPlaceTy<'tcx, Provenance>,
 ) -> InterpResult<'tcx, ()> {
-    let (num_chunks, items_per_chunk, left, right, dest) =
-        split_simd_to_128bit_chunks(this, left, right, dest)?;
+    assert_eq!(left.layout, dest.layout);
+    assert_eq!(right.layout, dest.layout);
+
+    let (num_chunks, items_per_chunk, left) = split_simd_to_128bit_chunks(this, left)?;
+    let (_, _, right) = split_simd_to_128bit_chunks(this, right)?;
+    let (_, _, dest) = split_simd_to_128bit_chunks(this, dest)?;
 
     let element_layout = left.layout.field(this, 0).field(this, 0);
     assert!(items_per_chunk <= 4);