Emit error on array size overflow

When the byte size required for an array overflow we should emit an
error.

gcc/rust/ChangeLog:

	* backend/rust-compile-expr.cc (CompileExpr::array_copied_expr): Check
	for overflow on array memory size and emit an error.

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3962.rs: New test.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

Author: P-E-P

gcc/rust/backend/rust-compile-expr.cc

@@ -2045,6 +2045,17 @@ CompileExpr::array_copied_expr (location_t expr_locus,
   unsigned HOST_WIDE_INT len
     = wi::ext (max - min + 1, precision, sign).to_uhwi ();
 
+  unsigned int res;
+  if (__builtin_umul_overflow (TREE_INT_CST_ELT (TYPE_SIZE_UNIT (array_type),
+						 0),
+			       len, &res))
+    {
+      rust_error_at (expr_locus, ErrorCode::E0080,
+		     "the type %qs is too big for the current architecture",
+		     array_tyty.as_string ().c_str ());
+      return error_mark_node;
+    }
+
   // In a const context we must initialize the entire array, which entails
   // allocating for each element. If the user wants a huge array, we will OOM
   // and die horribly.

gcc/testsuite/rust/compile/issue-3962.rs

@@ -0,0 +1,5 @@
+static FOO2: () = {
+    let x = [47; (1 << 47) - 1];
+    // { dg-error "the type ..i32; 140737488355327.. is too big for the current architecture" "" { target x86_64-*-* } .-1 }
+    // { dg-error "left shift count >= width of type" "" { target i?86-*-* } .-2 }
+};