[gcc/devel/rust/master] Allow references to arrays for ArrayIndexExpr accessor's

[Thomas Schwinge <tschwinge@gcc.gnu.org>]

https://gcc.gnu.org/g:e7e65bbdf3a06a7d00ed7da4ff8ebb16031ed6c3

commit e7e65bbdf3a06a7d00ed7da4ff8ebb16031ed6c3
Author: Philip Herron <philip.herron@embecosm.com>
Date:   Wed Nov 24 16:31:49 2021 +0000

    Allow references to arrays for ArrayIndexExpr accessor's
    
    When we have an array-index expr rust allows the array reference to be a
    reference and the compiler is meant to add in the required implicit
    indirection. This checks for this senario and injects the indirection
    during code-generation.
    
    Fixes #815

Diff:
---
 gcc/rust/backend/rust-compile-expr.h          | 26 ++++++++++++++++++++--
 gcc/rust/typecheck/rust-hir-type-check-expr.h | 32 +++++++++++++++------------
 gcc/testsuite/rust/compile/array3.rs          |  5 +++++
 3 files changed, 47 insertions(+), 16 deletions(-)

diff --git a/gcc/rust/backend/rust-compile-expr.h b/gcc/rust/backend/rust-compile-expr.h
index 2bf969beef9..46d501a5859 100644
--- a/gcc/rust/backend/rust-compile-expr.h
+++ b/gcc/rust/backend/rust-compile-expr.h
@@ -390,10 +390,32 @@ public:
 
   void visit (HIR::ArrayIndexExpr &expr) override
   {
-    tree array = CompileExpr::Compile (expr.get_array_expr (), ctx);
+    tree array_reference = CompileExpr::Compile (expr.get_array_expr (), ctx);
     tree index = CompileExpr::Compile (expr.get_index_expr (), ctx);
+
+    // lets check if the array is a reference type then we can add an
+    // indirection if required
+    TyTy::BaseType *array_expr_ty = nullptr;
+    bool ok = ctx->get_tyctx ()->lookup_type (
+      expr.get_array_expr ()->get_mappings ().get_hirid (), &array_expr_ty);
+    rust_assert (ok);
+
+    // do we need to add an indirect reference
+    if (array_expr_ty->get_kind () == TyTy::TypeKind::REF)
+      {
+	TyTy::ReferenceType *r
+	  = static_cast<TyTy::ReferenceType *> (array_expr_ty);
+	TyTy::BaseType *tuple_type = r->get_base ();
+	tree array_tyty = TyTyResolveCompile::compile (ctx, tuple_type);
+
+	array_reference
+	  = ctx->get_backend ()->indirect_expression (array_tyty,
+						      array_reference, true,
+						      expr.get_locus ());
+      }
+
     translated
-      = ctx->get_backend ()->array_index_expression (array, index,
+      = ctx->get_backend ()->array_index_expression (array_reference, index,
 						     expr.get_locus ());
   }
 
diff --git a/gcc/rust/typecheck/rust-hir-type-check-expr.h b/gcc/rust/typecheck/rust-hir-type-check-expr.h
index fb1cd972293..8c34b6c776a 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-expr.h
+++ b/gcc/rust/typecheck/rust-hir-type-check-expr.h
@@ -929,24 +929,27 @@ public:
 
     auto resolved_index_expr
       = size_ty->unify (TypeCheckExpr::Resolve (expr.get_index_expr (), false));
-    if (resolved_index_expr == nullptr)
+    if (resolved_index_expr->get_kind () != TyTy::TypeKind::ERROR)
       {
-	rust_error_at (expr.get_index_expr ()->get_locus (),
-		       "Type Resolver failure in Index for ArrayIndexExpr");
-	return;
+	// allow the index expr to fail lets just continue on
+	context->insert_type (expr.get_index_expr ()->get_mappings (),
+			      resolved_index_expr);
       }
-    context->insert_type (expr.get_index_expr ()->get_mappings (),
-			  resolved_index_expr);
 
-    // resolve the array reference
-    expr.get_array_expr ()->accept_vis (*this);
-    if (infered == nullptr)
+    auto array_expr_ty
+      = TypeCheckExpr::Resolve (expr.get_array_expr (), inside_loop);
+    if (array_expr_ty->get_kind () == TyTy::TypeKind::ERROR)
+      return;
+    else if (array_expr_ty->get_kind () == TyTy::TypeKind::REF)
       {
-	rust_error_at (expr.get_index_expr ()->get_locus (),
-		       "failed to resolve array reference expression");
-	return;
+	// lets try and deref it since rust allows this
+	auto ref = static_cast<TyTy::ReferenceType *> (array_expr_ty);
+	auto base = ref->get_base ();
+	if (base->get_kind () == TyTy::TypeKind::ARRAY)
+	  array_expr_ty = base;
       }
-    else if (infered->get_kind () != TyTy::TypeKind::ARRAY)
+
+    if (array_expr_ty->get_kind () != TyTy::TypeKind::ARRAY)
       {
 	rust_error_at (expr.get_index_expr ()->get_locus (),
 		       "expected an ArrayType got [%s]",
@@ -955,7 +958,8 @@ public:
 	return;
       }
 
-    TyTy::ArrayType *array_type = static_cast<TyTy::ArrayType *> (infered);
+    TyTy::ArrayType *array_type
+      = static_cast<TyTy::ArrayType *> (array_expr_ty);
     infered = array_type->get_element_type ()->clone ();
   }
 
diff --git a/gcc/testsuite/rust/compile/array3.rs b/gcc/testsuite/rust/compile/array3.rs
new file mode 100644
index 00000000000..a62c6ca69c7
--- /dev/null
+++ b/gcc/testsuite/rust/compile/array3.rs
@@ -0,0 +1,5 @@
+fn foo(state: &mut [u32; 16], a: usize) {
+    // { dg-warning "function is never used: .foo." "" { target *-*-* } .-1 }
+    // { dg-warning "unused name .foo." "" { target *-*-* } .-2 }
+    state[a] = 1;
+}