Move mir const to valtree conversion to its own method.

Author: oli-obk

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -863,22 +863,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         // promotes any complex rvalues to constants.
                         if i == 2 && intrinsic.as_str().starts_with("simd_shuffle") {
                             if let mir::Operand::Constant(constant) = arg {
-                                let ct = self.monomorphize(constant.literal);
-                                let uv = match ct {
-                                    mir::ConstantKind::Unevaluated(uv, _) => uv.shrink(),
-                                    other => span_bug!(constant.span, "{other:#?}"),
-                                };
-                                let c = self.cx.tcx().const_eval_resolve_for_typeck(
-                                    ty::ParamEnv::reveal_all(),
-                                    uv,
-                                    Some(constant.span),
-                                );
-                                let (llval, ty) = self.simd_shuffle_indices(
-                                    &bx,
-                                    constant.span,
-                                    self.monomorphize(constant.ty()),
-                                    c,
-                                );
+                                let (llval, ty) = self.simd_shuffle_indices(&bx, constant);
                                 return OperandRef {
                                     val: Immediate(llval),
                                     layout: bx.layout_of(ty),

compiler/rustc_codegen_ssa/src/mir/constant.rs

@@ -5,7 +5,6 @@ use rustc_middle::mir;
 use rustc_middle::mir::interpret::{ConstValue, ErrorHandled};
 use rustc_middle::ty::layout::HasTyCtxt;
 use rustc_middle::ty::{self, Ty};
-use rustc_span::source_map::Span;
 use rustc_target::abi::Abi;
 
 use super::FunctionCx;
@@ -59,15 +58,34 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         })
     }
 
+    /// This is a convenience helper for `simd_shuffle_indices`. It has the precondition
+    /// that the given `constant` is an `ConstantKind::Unevaluated` and must be convertible to
+    /// a `ValTree`. If you want a more general version of this, talk to `wg-const-eval` on zulip.
+    pub fn eval_unevaluated_mir_constant_to_valtree(
+        &self,
+        constant: &mir::Constant<'tcx>,
+    ) -> Result<Option<ty::ValTree<'tcx>>, ErrorHandled> {
+        let uv = match constant.literal {
+            mir::ConstantKind::Unevaluated(uv, _) => uv.shrink(),
+            other => span_bug!(constant.span, "{other:#?}"),
+        };
+        let uv = self.monomorphize(uv);
+        self.cx.tcx().const_eval_resolve_for_typeck(
+            ty::ParamEnv::reveal_all(),
+            uv,
+            Some(constant.span),
+        )
+    }
+
     /// process constant containing SIMD shuffle indices
     pub fn simd_shuffle_indices(
         &mut self,
         bx: &Bx,
-        span: Span,
-        ty: Ty<'tcx>,
-        constant: Result<Option<ty::ValTree<'tcx>>, ErrorHandled>,
+        constant: &mir::Constant<'tcx>,
     ) -> (Bx::Value, Ty<'tcx>) {
-        let val = constant
+        let ty = self.monomorphize(constant.ty());
+        let val = self
+            .eval_unevaluated_mir_constant_to_valtree(constant)
             .ok()
             .flatten()
             .map(|val| {
@@ -90,9 +108,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 bx.const_struct(&values, false)
             })
             .unwrap_or_else(|| {
-                bx.tcx().sess.emit_err(errors::ShuffleIndicesEvaluation { span });
+                bx.tcx().sess.emit_err(errors::ShuffleIndicesEvaluation { span: constant.span });
                 // We've errored, so we don't have to produce working code.
-                let ty = self.monomorphize(ty);
                 let llty = bx.backend_type(bx.layout_of(ty));
                 bx.const_undef(llty)
             });