[gcc r12-8301] i386: Fix up ix86_gimplify_va_arg [PR105331]

[gcc r12-8301] i386: Fix up ix86_gimplify_va_arg [PR105331]

[Jakub Jelinek]

https://gcc.gnu.org/g:89dbf9a5f55e0f7565865d1b38e681ef7d76afaf

commit r12-8301-g89dbf9a5f55e0f7565865d1b38e681ef7d76afaf
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Apr 28 12:33:59 2022 +0200

    i386: Fix up ix86_gimplify_va_arg [PR105331]
    
    On the following testcase we emit a bogus
    'va_arg_tmp.5' may be used uninitialized
    warning.  The reason is that when gimplifying the addr = &temp;
    statement, the va_arg_tmp temporary var for which we emit ADDR_EXPR
    is not TREE_ADDRESSABLE, prepare_gimple_addressable emits some extra
    code to initialize the newly addressable var from its previous value,
    but it is a new variable which hasn't been initialized yet and will
    be later, so we end up initializing it with uninitialized SSA_NAME:
      va_arg_tmp.6 = va_arg_tmp.5_14(D);
      addr.2_16 = &va_arg_tmp.6;
      _17 = MEM[(double *)sse_addr.4_13];
      MEM[(double * {ref-all})addr.2_16] = _17;
    and with -O1 we actually don't DSE it before the warning is emitted.
    If we make the temp TREE_ADDRESSABLE before the gimplification, then
    this prepare_gimple_addressable path isn't taken and we effectively
    omit the first statement above and so the bogus warning is gone.
    
    I went through other backends and didn't find another instance of this
    problem.
    
    2022-04-28  Jakub Jelinek  <jakub@redhat.com>
    
            PR target/105331
            * config/i386/i386.cc (ix86_gimplify_va_arg): Mark va_arg_tmp
            temporary TREE_ADDRESSABLE before trying to gimplify ADDR_EXPR
            of it.
    
            * gcc.dg/pr105331.c: New test.

Diff:
---
 gcc/config/i386/i386.cc         |  1 +
 gcc/testsuite/gcc.dg/pr105331.c | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index 52040da8c47..b16df5b183e 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -4891,6 +4891,7 @@ ix86_gimplify_va_arg (tree valist, tree type, gimple_seq *pre_p,
 	{
 	  int i, prev_size = 0;
 	  tree temp = create_tmp_var (type, "va_arg_tmp");
+	  TREE_ADDRESSABLE (temp) = 1;
 
 	  /* addr = &temp; */
 	  t = build1 (ADDR_EXPR, build_pointer_type (type), temp);
diff --git a/gcc/testsuite/gcc.dg/pr105331.c b/gcc/testsuite/gcc.dg/pr105331.c
new file mode 100644
index 00000000000..06cf6d6d901
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr105331.c
@@ -0,0 +1,11 @@
+/* PR target/105331 */
+/* { dg-do compile } */
+/* { dg-options "-O -Wuninitialized" } */
+
+#include <stdarg.h>
+
+int
+foo (va_list *va)
+{
+  return va_arg (*va, double _Complex);	/* { dg-bogus "may be used uninitialized" } */
+}