Monomorphize constants before inspecting them

(cherry picked from commit c7428d5)

Author: oli-obk

compiler/rustc_codegen_ssa/src/mir/constant.rs

@@ -65,7 +65,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         &self,
         constant: &mir::Constant<'tcx>,
     ) -> Result<Option<ty::ValTree<'tcx>>, ErrorHandled> {
-        let uv = match constant.literal {
+        let uv = match self.monomorphize(constant.literal) {
             mir::ConstantKind::Unevaluated(uv, _) => uv.shrink(),
             mir::ConstantKind::Ty(c) => match c.kind() {
                 // A constant that came from a const generic but was then used as an argument to old-style

tests/ui/simd/shuffle.rs

@@ -1,4 +1,7 @@
-//run-pass
+// run-pass
+// revisions: opt noopt
+//[noopt] compile-flags: -Copt-level=0
+//[opt] compile-flags: -O
 #![feature(repr_simd, platform_intrinsics)]
 #![allow(incomplete_features)]
 #![feature(adt_const_params)]