Rollup merge of rust-lang#118844 - celinval:smir-mono-args, r=compile…

…r-errors

Monomorphize args while building Instance body in StableMIR

The function `Instance::body()` in StableMIR is supposed to return a monomorphic body by instantiating all possibly generic constructs. We were previously instantiating type and constants, but not generic arguments. This PR ensures that we also instantiate them.

r? `@compiler-errors`

compiler/rustc_smir/src/rustc_smir/builder.rs

@@ -6,7 +6,7 @@
 use crate::rustc_smir::{Stable, Tables};
 use rustc_middle::mir;
 use rustc_middle::mir::visit::MutVisitor;
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt};
 
 /// Builds a monomorphic body for a given instance.
 pub struct BodyBuilder<'tcx> {
@@ -68,6 +68,10 @@ impl<'tcx> MutVisitor<'tcx> for BodyBuilder<'tcx> {
         self.super_constant(constant, location);
     }
 
+    fn visit_args(&mut self, args: &mut GenericArgsRef<'tcx>, _: mir::Location) {
+        *args = self.monomorphize(*args);
+    }
+
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }