On 9/29/21 17:30, Qing Zhao wrote:
Hi,
PR102359 (ICE gimplification failed since r12-3433-ga25e0b5e6ac8a77a)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102359
Is due to -ftrivial-auto-var-init adding initialization for READONLY variable
“this” in the following routine: (t.cpp.005t.original)
=======
;; Function A::foo()::<lambda()> (null)
;; enabled by -tree-original
{
const struct A * const this [value-expr: &__closure->__this];
const struct A * const this [value-expr: &__closure->__this];
return <retval> = (double) ((const struct A *) this)->a;
}
=======
However, in the above routine, “this” is NOT marked as READONLY, but its value-expr
"&__closure->__this” is marked as READONLY.
There are two major issues:
1. In the routine “is_var_need_auto_init”, we should exclude “decl” that is
marked as READONLY;
2. In the C++ FE, “this” should be marked as READONLY.
The idea solution will be:
1. Fix “is_var_need_auto_init” to exclude TREE_READONLY (decl);
2. Fix C++ FE to mark “this” as TREE_READONLY (decl)==true;
Not sure whether it’s hard for C++ FE to fix the 2nd issue or not?
In the case it’s not a quick fix in C++FE, I proposed the following fix in
middle end:
Let me know your comments or suggestions on this.
Thanks a lot for the help.
I'd think is_var_need_auto_init should be false for any variable with
DECL_HAS_VALUE_EXPR_P, as they aren't really variables, just ways of
naming objects that are initialized elsewhere.
Qing
==============================
From 0a5982cd61bc4610655d3df00ae8d2fbcb3c8e9b Mon Sep 17 00:00:00 2001
From: Qing Zhao <qing.z...@oracle.com>
Date: Wed, 29 Sep 2021 20:49:59 +0000
Subject: [PATCH] Fix PR102359
---
gcc/gimplify.c | 15 +++++++++++++++
gcc/testsuite/g++.dg/pr102359.C | 13 +++++++++++++
2 files changed, 28 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/pr102359.C
diff --git a/gcc/gimplify.c b/gcc/gimplify.c
index 1067113b1639..a2587869b35d 100644
--- a/gcc/gimplify.c
+++ b/gcc/gimplify.c
@@ -1819,12 +1819,27 @@ gimple_add_padding_init_for_auto_var (tree decl, bool
is_vla,
gimplify_seq_add_stmt (seq_p, call);
}
+/* Return true if the DECL is READONLY.
+ This is to workaround a C++ FE bug that only mark the value_expr of "this"
+ as readonly but does not mark "this" as readonly.
+ C++ FE should fix this issue before replacing this routine with
+ TREE_READONLY (decl). */
+
+static bool
+is_decl_readonly (tree decl)
+{
+ return (TREE_READONLY (decl)
+ || (DECL_HAS_VALUE_EXPR_P (decl)
+ && TREE_READONLY (DECL_VALUE_EXPR (decl))));
+}
+
/* Return true if the DECL need to be automaticly initialized by the
compiler. */
static bool
is_var_need_auto_init (tree decl)
{
if (auto_var_p (decl)
+ && !is_decl_readonly (decl)
&& (flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
&& (!lookup_attribute ("uninitialized", DECL_ATTRIBUTES (decl)))
&& !is_empty_type (TREE_TYPE (decl)))
diff --git a/gcc/testsuite/g++.dg/pr102359.C b/gcc/testsuite/g++.dg/pr102359.C
new file mode 100644
index 000000000000..da643cde7bed
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr102359.C
@@ -0,0 +1,13 @@
+/* PR middle-end/102359 ICE gimplification failed since
+ r12-3433-ga25e0b5e6ac8a77a. */
+/* { dg-do compile } */
+/* { dg-options "-ftrivial-auto-var-init=zero" } */
+/* { dg-require-effective-target c++17 } */
+
+struct A {
+ double a = 111;
+ auto foo() {
+ return [*this] { return a; };
+ }
+};
+int X = A{}.foo()();
