From afa451b311dec27476941e6f307d04450d28ab88 Mon Sep 17 00:00:00 2001
From: Philip Herron <philip.herron@embecosm.com>
Date: Mon, 21 Mar 2022 12:40:20 +0000
Subject: Add initial support for unsized method resolution

In order to support slices, we end up with an operator overload call of:

```
impl<T, I> Index<I> for [T]
where
    I: SliceIndex<[T]>,
{
    type Output = I::Output;

    fn index(&self, index: I) -> &I::Output {
        index.index(self)
    }
}
```

So this means the self in this case is an array[T,capacity] and the index parameter is of type Range<usize>. In order to actually call this method
which has a self parameter of [T] we need to be able to 'unsize' the array
into a slice.

Addresses #849
---
 gcc/rust/backend/rust-compile-base.h  |  3 +++
 gcc/rust/backend/rust-compile-expr.cc | 30 ++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

(limited to 'gcc/rust/backend')

diff --git a/gcc/rust/backend/rust-compile-base.h b/gcc/rust/backend/rust-compile-base.h
index c30aa4d..c7f7f40 100644
--- a/gcc/rust/backend/rust-compile-base.h
+++ b/gcc/rust/backend/rust-compile-base.h
@@ -72,6 +72,9 @@ protected:
   tree resolve_indirection_adjustment (Resolver::Adjustment &adjustment,
 				       tree expression, Location locus);
 
+  tree resolve_unsized_adjustment (Resolver::Adjustment &adjustment,
+				   tree expression, Location locus);
+
   static void setup_attributes_on_fndecl (
     tree fndecl, bool is_main_entry_point, HIR::Visibility &visibility,
     const HIR::FunctionQualifiers &qualifiers, const AST::AttrVec &attrs);
diff --git a/gcc/rust/backend/rust-compile-expr.cc b/gcc/rust/backend/rust-compile-expr.cc
index 03e3c2e..74ab6a4 100644
--- a/gcc/rust/backend/rust-compile-expr.cc
+++ b/gcc/rust/backend/rust-compile-expr.cc
@@ -1204,6 +1204,10 @@ HIRCompileBase::resolve_adjustements (
 	case Resolver::Adjustment::AdjustmentType::INDIRECTION:
 	  e = resolve_indirection_adjustment (adjustment, e, locus);
 	  break;
+
+	case Resolver::Adjustment::AdjustmentType::UNSIZE:
+	  e = resolve_unsized_adjustment (adjustment, e, locus);
+	  break;
 	}
     }
 
@@ -1257,6 +1261,32 @@ HIRCompileBase::resolve_indirection_adjustment (
 						   locus);
 }
 
+tree
+HIRCompileBase::resolve_unsized_adjustment (Resolver::Adjustment &adjustment,
+					    tree expression, Location locus)
+{
+  // assumes this is an array
+  tree expr_type = TREE_TYPE (expression);
+  rust_assert (TREE_CODE (expr_type) == ARRAY_TYPE);
+
+  // takes an array and returns a fat-pointer so this becomes a constructor
+  // expression
+  rust_assert (adjustment.get_expected ()->get_kind ()
+	       == TyTy::TypeKind::SLICE);
+  tree fat_pointer
+    = TyTyResolveCompile::compile (ctx, adjustment.get_expected ());
+
+  // make a constructor for this
+  tree data = address_expression (expression, locus);
+
+  // fetch the size from the domain
+  tree domain = TYPE_DOMAIN (expr_type);
+  tree size = TYPE_MAX_VALUE (domain);
+
+  return ctx->get_backend ()->constructor_expression (fat_pointer, false,
+						      {data, size}, -1, locus);
+}
+
 void
 CompileExpr::visit (HIR::IdentifierExpr &expr)
 {
-- 
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