Rollup merge of #128731 - RalfJung:simd-shuffle-vector, r=workingjubilee

simd_shuffle intrinsic: allow argument to be passed as vector

See https://github.com/rust-lang/rust/issues/128738 for context.

I'd like to get rid of [this hack](https://github.com/rust-lang/rust/blob/6c0b89dfac65be9a5be12f938f23098ebc36c635/compiler/rustc_codegen_ssa/src/mir/block.rs#L922-L935). https://github.com/rust-lang/rust/pull/128537 almost lets us do that since constant SIMD vectors will then be passed as immediate arguments. However, simd_shuffle for some reason actually takes an *array* as argument, not a vector, so the hack is still required to ensure that the array becomes an immediate (which then later stages of codegen convert into a vector, as that's what LLVM needs).

This PR prepares simd_shuffle to also support a vector as the `idx` argument. Once this lands, stdarch can hopefully be updated to pass `idx` as a vector, and then support for arrays can be removed, which finally lets us get rid of that hack.

1 files changed, 12 insertions, 7 deletions

diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index abfe38d4c0c..a300f5f707a 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -1287,19 +1287,24 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
     }
 
     if name == sym::simd_shuffle {
-        // Make sure this is actually an array, since typeck only checks the length-suffixed
+        // Make sure this is actually an array or SIMD vector, since typeck only checks the length-suffixed
         // version of this intrinsic.
-        let n: u64 = match args[2].layout.ty.kind() {
+        let idx_ty = args[2].layout.ty;
+        let n: u64 = match idx_ty.kind() {
             ty::Array(ty, len) if matches!(ty.kind(), ty::Uint(ty::UintTy::U32)) => {
                 len.try_eval_target_usize(bx.cx.tcx, ty::ParamEnv::reveal_all()).unwrap_or_else(
                     || span_bug!(span, "could not evaluate shuffle index array length"),
                 )
             }
-            _ => return_error!(InvalidMonomorphization::SimdShuffle {
-                span,
-                name,
-                ty: args[2].layout.ty
-            }),
+            _ if idx_ty.is_simd()
+                && matches!(
+                    idx_ty.simd_size_and_type(bx.cx.tcx).1.kind(),
+                    ty::Uint(ty::UintTy::U32)
+                ) =>
+            {
+                idx_ty.simd_size_and_type(bx.cx.tcx).0
+            }
+            _ => return_error!(InvalidMonomorphization::SimdShuffle { span, name, ty: idx_ty }),
         };
 
         let (out_len, out_ty) = require_simd!(ret_ty, SimdReturn);