[1/2,middle-end/102276] Don't emit switch-unreachable warnings for -ftrivial-auto-var-init (PR102276)
Commit Message
Ping.
Qing
Begin forwarded message:
From: Qing Zhao via Gcc-patches <gcc-patches@gcc.gnu.org<mailto:gcc-patches@gcc.gnu.org>>
Subject: [PATCH 1/2][middle-end/102276] Don't emit switch-unreachable warnings for -ftrivial-auto-var-init (PR102276)
Date: February 19, 2022 at 10:22:43 AM CST
To: richard Biener <rguenther@suse.de<mailto:rguenther@suse.de>>, jakub Jelinek <jakub@redhat.com<mailto:jakub@redhat.com>>
Cc: gcc-patches Paul A Clarke via <gcc-patches@gcc.gnu.org<mailto:gcc-patches@gcc.gnu.org>>, kees Cook <keescook@chromium.org<mailto:keescook@chromium.org>>
Reply-To: Qing Zhao <qing.zhao@oracle.com<mailto:qing.zhao@oracle.com>>
Hi,
Per our discussion in the bug report https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102276
We decided to go with the following solution:
1. avoid emitting switch-unreachable warnings for -ftrivial-auto-var-init;
2. adding a new option -Wtrivial-auto-var-init to emit warnings for the switch-unreadable cases to suggest the user modify the source code;
3. update documentation of -ftrivial-auto-var-init for the limitation on switch-unreachable cases and introduce the new option -Wtrivial-auto-var-init
with the above 1, we can resolve the current immediate issue of spurious warnings of using -ftrivial-auto-var-init to make kernel build succeed;
with the above 2, we provide the user a way to know that -ftrivial-auto-var-init has limitation on the switch-unreachable cases, and user should modify the source code to avoid this problem;
with the above 3, we will provide the user a clear documentation of the -ftrivial-auto-var-init and also provide suggestions how to resolve this issue.
There are two patches included for this bug. This is the first one.
The patches has been bootstrapped and regression tested on both x86 and aarch64.
Okay for commit?
Thanks.
Qing.
===========================
From 65bc9607ff35ad49e5501ec5c392293c5b6358d0 Mon Sep 17 00:00:00 2001
From: Qing Zhao <qing.zhao@oracle.com<mailto:qing.zhao@oracle.com>>
Date: Fri, 18 Feb 2022 15:35:53 +0000
Subject: [PATCH 1/2] Don't emit switch-unreachable warnings for
-ftrivial-auto-var-init (PR102276)
for the following testing case:
1 int g(int *);
2 int f1()
3 {
4 switch (0) {
5 int x;
6 default:
7 return g(&x);
8 }
9 }
compiling with -O -ftrivial-auto-var-init causes spurious warning:
warning: statement will never be executed [-Wswitch-unreachable]
5 | int x;
| ^
This is due to the compiler-generated initialization at the point of
the declaration.
We could avoid the warning by adjusting the routine
"maybe_warn_switch_unreachable" to exclude the following cases:
when
flag_auto_var_init > AUTO_INIT_UNINITIALIZED
And
call to .DEFERRED_INIT
2022-02-18 Qing Zhao <qing.zhao@oracle.com<mailto:qing.zhao@oracle.com>>
gcc/ChangeLog:
* gimplify.cc<http://gimplify.cc> (maybe_warn_switch_unreachable): Don't warn for compiler
-generated initializations for -ftrivial-auto-var-init.
gcc/testsuite/ChangeLog:
* gcc.dg/auto-init-pr102276-1.c: New test.
* gcc.dg/auto-init-pr102276-2.c: New test.
---
gcc/gimplify.cc<http://gimplify.cc> | 8 ++++-
gcc/testsuite/gcc.dg/auto-init-pr102276-1.c | 38 +++++++++++++++++++++
gcc/testsuite/gcc.dg/auto-init-pr102276-2.c | 38 +++++++++++++++++++++
3 files changed, 83 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-1.c
create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-2.c
--
2.27.0
@@ -2103,7 +2103,13 @@ maybe_warn_switch_unreachable (gimple_seq seq)
&& TREE_CODE (gimple_goto_dest (stmt)) == LABEL_DECL
&& DECL_ARTIFICIAL (gimple_goto_dest (stmt)))
/* Don't warn for compiler-generated gotos. These occur
- in Duff's devices, for example. */;
+ in Duff's devices, for example. */
+ ;
+ else if ((flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
+ && (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)))
+ /* Don't warn for compiler-generated initializations for
+ -ftrivial-auto-var-init. */
+ ;
else
warning_at (gimple_location (stmt), OPT_Wswitch_unreachable,
"statement will never be executed");
new file mode 100644
@@ -0,0 +1,38 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wall -ftrivial-auto-var-init=zero" } */
+
+int g(int *);
+int f()
+{
+ switch (0) {
+ int x; /* { dg-bogus "statement will never be executed" } */
+ default:
+ return g(&x);
+ }
+}
+
+int g1(int);
+int f1()
+{
+ switch (0) {
+ int x; /* { dg-bogus "statement will never be executed" } */
+ default:
+ return g1(x); /* { dg-warning "is used uninitialized" } */
+ }
+}
+
+struct S
+{
+ char a;
+ int b;
+};
+int g2(int);
+int f2(int input)
+{
+ switch (0) {
+ struct S x; /* { dg-bogus "statement will never be executed" } */
+ default:
+ return g2(input) + x.b; /* { dg-warning "is used uninitialized" } */
+ }
+}
+
new file mode 100644
@@ -0,0 +1,38 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wall -ftrivial-auto-var-init=pattern" } */
+
+int g(int *);
+int f()
+{
+ switch (0) {
+ int x; /* { dg-bogus "statement will never be executed" } */
+ default:
+ return g(&x);
+ }
+}
+
+int g1(int);
+int f1()
+{
+ switch (0) {
+ int x; /* { dg-bogus "statement will never be executed" } */
+ default:
+ return g1(x); /* { dg-warning "is used uninitialized" } */
+ }
+}
+
+struct S
+{
+ char a;
+ int b;
+};
+int g2(int);
+int f2(int input)
+{
+ switch (0) {
+ struct S x; /* { dg-bogus "statement will never be executed" } */
+ default:
+ return g2(input) + x.b; /* { dg-warning "is used uninitialized" } */
+ }
+}
+