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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.
This commit is contained in:
Jakub Jelinek 2022-04-28 12:33:59 +02:00
parent 8094526109
commit 89dbf9a5f5
2 changed files with 12 additions and 0 deletions
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1
gcc/config/i386/i386.cc
View File

@ -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);

11
gcc/testsuite/gcc.dg/pr105331.c Normal file
View File

@ -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" } */
}