[gcc r12-7411] Suppress uninitialized warnings for new created uses from __builtin_clear_padding folding [PR104550]

[Qing Zhao <qinzhao@gcc.gnu.org>]

https://gcc.gnu.org/g:3f3246eb16f554c70c5ce87ad2c785f83adb4625

commit r12-7411-g3f3246eb16f554c70c5ce87ad2c785f83adb4625
Author: Qing Zhao <qing.zhao@oracle.com>
Date:   Mon Feb 28 15:58:43 2022 +0000

    Suppress uninitialized warnings for new created uses from __builtin_clear_padding folding [PR104550]
    
    __builtin_clear_padding(&object) will clear all the padding bits of the object.
    actually, it doesn't involve any use of an user variable. Therefore, users do
    not expect any uninitialized warning from it. It's reasonable to suppress
    uninitialized warnings for all new created uses from __builtin_clear_padding
    folding.
    
            PR middle-end/104550
    
    gcc/ChangeLog:
    
            * gimple-fold.cc (clear_padding_flush): Suppress warnings for new
            created uses.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/auto-init-pr104550-1.c: New test.
            * gcc.dg/auto-init-pr104550-2.c: New test.
            * gcc.dg/auto-init-pr104550-3.c: New test.

Diff:
---
 gcc/gimple-fold.cc                          | 12 +++++++++++-
 gcc/testsuite/gcc.dg/auto-init-pr104550-1.c | 10 ++++++++++
 gcc/testsuite/gcc.dg/auto-init-pr104550-2.c | 11 +++++++++++
 gcc/testsuite/gcc.dg/auto-init-pr104550-3.c | 11 +++++++++++
 4 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
index 16f02c2d098..c9179abb27e 100644
--- a/gcc/gimple-fold.cc
+++ b/gcc/gimple-fold.cc
@@ -4379,7 +4379,17 @@ clear_padding_flush (clear_padding_struct *buf, bool full)
 	      else
 		{
 		  src = make_ssa_name (type);
-		  g = gimple_build_assign (src, unshare_expr (dst));
+		  tree tmp_dst = unshare_expr (dst);
+		  /* The folding introduces a read from the tmp_dst, we should
+		     prevent uninitialized warning analysis from issuing warning
+		     for such fake read.  In order to suppress warning only for
+		     this expr, we should set the location of tmp_dst to
+		     UNKNOWN_LOCATION first, then suppress_warning will call
+		     set_no_warning_bit to set the no_warning flag only for
+		     tmp_dst.  */
+		  SET_EXPR_LOCATION (tmp_dst, UNKNOWN_LOCATION);
+		  suppress_warning (tmp_dst, OPT_Wuninitialized);
+		  g = gimple_build_assign (src, tmp_dst);
 		  gimple_set_location (g, buf->loc);
 		  gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
 		  tree mask = native_interpret_expr (type,
diff --git a/gcc/testsuite/gcc.dg/auto-init-pr104550-1.c b/gcc/testsuite/gcc.dg/auto-init-pr104550-1.c
new file mode 100644
index 00000000000..a08110c3a17
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/auto-init-pr104550-1.c
@@ -0,0 +1,10 @@
+/* PR 104550*/
+/* { dg-do compile } */
+/* { dg-options "-O -Wuninitialized -ftrivial-auto-var-init=pattern" } */
+struct vx_audio_level {
+ int has_monitor_level : 1;
+};
+
+void vx_set_monitor_level() {
+ struct vx_audio_level info; /* { dg-bogus "info" "is used uninitialized" } */
+}
diff --git a/gcc/testsuite/gcc.dg/auto-init-pr104550-2.c b/gcc/testsuite/gcc.dg/auto-init-pr104550-2.c
new file mode 100644
index 00000000000..2c395b32d32
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/auto-init-pr104550-2.c
@@ -0,0 +1,11 @@
+/* PR 104550 */
+/* { dg-do compile } */
+/* { dg-options "-O -Wuninitialized -ftrivial-auto-var-init=zero" } */
+struct vx_audio_level {
+ int has_monitor_level : 1;
+};
+
+void vx_set_monitor_level() {
+ struct vx_audio_level info; 
+ __builtin_clear_padding (&info);  /* { dg-bogus "info" "is used uninitialized" } */ 
+}
diff --git a/gcc/testsuite/gcc.dg/auto-init-pr104550-3.c b/gcc/testsuite/gcc.dg/auto-init-pr104550-3.c
new file mode 100644
index 00000000000..9893e37f12d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/auto-init-pr104550-3.c
@@ -0,0 +1,11 @@
+/* PR 104550 */
+/* { dg-do compile } */
+/* { dg-options "-O -Wuninitialized -ftrivial-auto-var-init=pattern" } */
+struct vx_audio_level {
+ int has_monitor_level : 1;
+};
+
+void vx_set_monitor_level() {
+ struct vx_audio_level info;   /* { dg-bogus "info" "is used uninitialized" } */
+ __builtin_clear_padding (&info);  /* { dg-bogus "info" "is used uninitialized" } */ 
+}