light touch implementation of const vector

Author: Jamesbarford

compiler/rustc_codegen_gcc/src/common.rs

@@ -160,6 +160,11 @@ impl<'gcc, 'tcx> ConstMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         self.context.new_struct_constructor(None, struct_type.as_type(), None, values)
     }
 
+    fn const_vector(&self, values: &[RValue<'gcc>]) -> RValue<'gcc> {
+        let typ = self.type_vector(values[0].get_type(), values.len() as u64);
+        self.context.new_rvalue_from_vector(None, typ, values)
+    }
+
     fn const_to_opt_uint(&self, _v: RValue<'gcc>) -> Option<u64> {
         // TODO(antoyo)
         None

compiler/rustc_codegen_llvm/src/common.rs

@@ -224,6 +224,10 @@ impl<'ll, 'tcx> ConstMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         struct_in_context(self.llcx, elts, packed)
     }
 
+    fn const_vector(&self, elts: &[&'ll Value]) -> &'ll Value {
+        unsafe { llvm::LLVMConstVector(elts.as_ptr(), elts.len() as c_uint) }
+    }
+
     fn const_to_opt_uint(&self, v: &'ll Value) -> Option<u64> {
         try_as_const_integral(v).and_then(|v| unsafe {
             let mut i = 0u64;

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -924,7 +924,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         // checked by the type-checker.
                         if i == 2 && intrinsic.name == sym::simd_shuffle {
                             if let mir::Operand::Constant(constant) = &arg.node {
-                                let (llval, ty) = self.simd_shuffle_indices(bx, constant);
+                                let (llval, ty) = self.immediate_const_vector(bx, constant);
                                 return OperandRef {
                                     val: Immediate(llval),
                                     layout: bx.layout_of(ty),

compiler/rustc_codegen_ssa/src/mir/constant.rs

@@ -1,6 +1,6 @@
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::layout::HasTyCtxt;
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty::{self, Ty, ValTree};
 use rustc_middle::{bug, mir, span_bug};
 use rustc_target::abi::Abi;
 
@@ -28,7 +28,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             .expect("erroneous constant missed by mono item collection")
     }
 
-    /// This is a convenience helper for `simd_shuffle_indices`. It has the precondition
+    /// This is a convenience helper for `immediate_const_vector`. It has the precondition
     /// that the given `constant` is an `Const::Unevaluated` and must be convertible to
     /// a `ValTree`. If you want a more general version of this, talk to `wg-const-eval` on zulip.
     ///
@@ -59,23 +59,33 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         self.cx.tcx().const_eval_resolve_for_typeck(ty::ParamEnv::reveal_all(), uv, constant.span)
     }
 
-    /// process constant containing SIMD shuffle indices
-    pub fn simd_shuffle_indices(
+    /// process constant containing SIMD shuffle indices & constant vectors
+    pub fn immediate_const_vector(
         &mut self,
         bx: &Bx,
         constant: &mir::ConstOperand<'tcx>,
     ) -> (Bx::Value, Ty<'tcx>) {
         let ty = self.monomorphize(constant.ty());
+        let ty_is_simd = ty.is_simd();
+        let field_ty = if ty_is_simd {
+            ty.simd_size_and_type(bx.tcx()).1
+        } else {
+            ty.builtin_index().unwrap()
+        };
+
         let val = self
             .eval_unevaluated_mir_constant_to_valtree(constant)
             .ok()
             .map(|x| x.ok())
             .flatten()
             .map(|val| {
-                let field_ty = ty.builtin_index().unwrap();
-                let values: Vec<_> = val
-                    .unwrap_branch()
-                    .iter()
+                let field_iter = val.unwrap_branch();
+                let first = field_iter.get(0).unwrap();
+                let field_iter = match first {
+                    ValTree::Branch(_) => first.unwrap_branch().iter(),
+                    ValTree::Leaf(_) => field_iter.iter(),
+                };
+                let values: Vec<_> = field_iter
                     .map(|field| {
                         if let Some(prim) = field.try_to_scalar() {
                             let layout = bx.layout_of(field_ty);
@@ -84,11 +94,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                             };
                             bx.scalar_to_backend(prim, scalar, bx.immediate_backend_type(layout))
                         } else {
-                            bug!("simd shuffle field {:?}", field)
+                            bug!("field is not a scalar {:?}", field)
                         }
                     })
                     .collect();
-                bx.const_struct(&values, false)
+                if ty_is_simd { bx.const_vector(&values) } else { bx.const_struct(&values, false) }
             })
             .unwrap_or_else(|| {
                 bx.tcx().dcx().emit_err(errors::ShuffleIndicesEvaluation { span: constant.span });

compiler/rustc_codegen_ssa/src/traits/consts.rs

@@ -30,6 +30,7 @@ pub trait ConstMethods<'tcx>: BackendTypes {
 
     fn const_str(&self, s: &str) -> (Self::Value, Self::Value);
     fn const_struct(&self, elts: &[Self::Value], packed: bool) -> Self::Value;
+    fn const_vector(&self, elts: &[Self::Value]) -> Self::Value;
 
     fn const_to_opt_uint(&self, v: Self::Value) -> Option<u64>;
     fn const_to_opt_u128(&self, v: Self::Value, sign_ext: bool) -> Option<u128>;