diff mbox series

i386: Fix up ix86_gimplify_va_arg [PR105331]

Message ID YmJYTyEtsqlTwhKM@tucnak
State New
Headers show
Series i386: Fix up ix86_gimplify_va_arg [PR105331] | expand

Commit Message

Jakub Jelinek April 22, 2022, 7:25 a.m. UTC 
Hi!

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.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2022-04-22  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.


	Jakub

Comments

Jakub Jelinek April 28, 2022, 8:31 a.m. UTC | #1 
Hi!

I'd like to ping this patch.  I know it isn't a full week yet, but we are
almost out of P1s and GCC 12 branching is any time now.

Thanks:
On Fri, Apr 22, 2022 at 09:25:04AM +0200, Jakub Jelinek via Gcc-patches wrote:
> 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.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> 
> 2022-04-22  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.

	Jakub
Uros Bizjak April 28, 2022, 8:39 a.m. UTC | #2 
On Thu, Apr 28, 2022 at 10:31 AM Jakub Jelinek <jakub@redhat.com> wrote:
>
> Hi!
>
> I'd like to ping this patch.  I know it isn't a full week yet, but we are
> almost out of P1s and GCC 12 branching is any time now.
>
> Thanks:
> On Fri, Apr 22, 2022 at 09:25:04AM +0200, Jakub Jelinek via Gcc-patches wrote:
> > 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.
> >
> > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> >
> > 2022-04-22  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.

Sorry, I have no idea if this patch is correct or not.

Uros.
Jakub Jelinek April 28, 2022, 10:30 a.m. UTC | #3 
On Thu, Apr 28, 2022 at 10:39:39AM +0200, Uros Bizjak wrote:
> > > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> > >
> > > 2022-04-22  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.
> 
> Sorry, I have no idea if this patch is correct or not.

Richard or Jeff, could you please review it instead?

Thanks.

	Jakub
Richard Biener April 28, 2022, 10:31 a.m. UTC | #4 
On Thu, 28 Apr 2022, Jakub Jelinek wrote:

> On Thu, Apr 28, 2022 at 10:39:39AM +0200, Uros Bizjak wrote:
> > > > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> > > >
> > > > 2022-04-22  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.
> > 
> > Sorry, I have no idea if this patch is correct or not.
> 
> Richard or Jeff, could you please review it instead?

OK.

Thanks,
Richard.
Jeff Law April 28, 2022, 1:16 p.m. UTC | #5 
On 4/28/2022 4:31 AM, Richard Biener wrote:
> On Thu, 28 Apr 2022, Jakub Jelinek wrote:
>
>> On Thu, Apr 28, 2022 at 10:39:39AM +0200, Uros Bizjak wrote:
>>>>> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>>>>>
>>>>> 2022-04-22  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.
>>> Sorry, I have no idea if this patch is correct or not.
>> Richard or Jeff, could you please review it instead?
> OK.
Agreed.  In fact I'd fixed something very similar in our port a while ago.

Jeff
diff mbox series

Patch

--- gcc/config/i386/i386.cc.jj	2022-04-12 09:20:07.566662842 +0200
+++ gcc/config/i386/i386.cc	2022-04-21 12:03:32.201951522 +0200
@@ -4891,6 +4891,7 @@  ix86_gimplify_va_arg (tree valist, tree
 	{
 	  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);
--- gcc/testsuite/gcc.dg/pr105331.c.jj	2022-04-21 12:09:34.398906718 +0200
+++ gcc/testsuite/gcc.dg/pr105331.c	2022-04-21 12:09:07.304283903 +0200
@@ -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" } */
+}