Rollup merge of #122480 - oli-obk:const-eval-span-no-opt, r=RalfJung

Avoid various uses of `Option<Span>` in favor of using `DUMMY_SP` in the few cases that used `None`

based on #122471

`DUMMY_SP` is already the sentinel value we have that says "no span". We don't need to wrap these `Span`s in a separate `Option`.

Author: matthiaskrgr

src/machine.rs

@@ -1503,15 +1503,15 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
     fn eval_mir_constant<F>(
         ecx: &InterpCx<'mir, 'tcx, Self>,
         val: mir::Const<'tcx>,
-        span: Option<Span>,
+        span: Span,
         layout: Option<TyAndLayout<'tcx>>,
         eval: F,
     ) -> InterpResult<'tcx, OpTy<'tcx, Self::Provenance>>
     where
         F: Fn(
             &InterpCx<'mir, 'tcx, Self>,
             mir::Const<'tcx>,
-            Option<Span>,
+            Span,
             Option<TyAndLayout<'tcx>>,
         ) -> InterpResult<'tcx, OpTy<'tcx, Self::Provenance>>,
     {

src/shims/intrinsics/simd.rs

@@ -549,7 +549,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
                 let index = generic_args[2]
                     .expect_const()
-                    .eval(*this.tcx, this.param_env(), Some(this.tcx.span))
+                    .eval(*this.tcx, this.param_env(), this.tcx.span)
                     .unwrap()
                     .unwrap_branch();
                 let index_len = index.len();