[PATCH] middle-end/111422 - wrong stack var coalescing, handle PHIs

[PATCH] middle-end/111422 - wrong stack var coalescing, handle PHIs

[Richard Biener]

The gcc.c-torture/execute/pr111422.c testcase after installing the
sink pass improvement reveals that we also need to handle

 _65 = &g + _58;              _44 = &g + _43;
 # _59 = PHI <_65, _44>
 *_59 = 8;
 g = {v} {CLOBBER(eos)};
 ...
 n[0] = &f;
 *_59 = 8;
 g = {v} {CLOBBER(eos)};

where we fail to see the conflict between n and g after the first
clobber of g.  Before the sinking improvement there was a conflict
recorded on a path where _65/_44 are unused, so the real conflict
was missed but the fake one avoided the miscompile.

The following handles PHI defs in add_scope_conflicts_2 which
fixes the issue.

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

OK if that succeeds?

Thanks,
Richard.

	PR middle-end/111422
	* cfgexpand.cc (add_scope_conflicts_2): Handle PHIs
	by recursing to their arguments.
---
 gcc/cfgexpand.cc | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/gcc/cfgexpand.cc b/gcc/cfgexpand.cc
index 557cb28733b..e4d763fa998 100644
--- a/gcc/cfgexpand.cc
+++ b/gcc/cfgexpand.cc
@@ -584,10 +584,23 @@ add_scope_conflicts_2 (tree use, bitmap work,
 	  || INTEGRAL_TYPE_P (TREE_TYPE (use))))
     {
       gimple *g = SSA_NAME_DEF_STMT (use);
-      if (is_gimple_assign (g))
-	if (tree op = gimple_assign_rhs1 (g))
-	  if (TREE_CODE (op) == ADDR_EXPR)
-	    visit (g, TREE_OPERAND (op, 0), op, work);
+      if (gassign *a = dyn_cast <gassign *> (g))
+	{
+	  if (tree op = gimple_assign_rhs1 (a))
+	    if (TREE_CODE (op) == ADDR_EXPR)
+	      visit (a, TREE_OPERAND (op, 0), op, work);
+	}
+      else if (gphi *p = dyn_cast <gphi *> (g))
+	{
+	  for (unsigned i = 0; i < gimple_phi_num_args (p); ++i)
+	    if (TREE_CODE (use = gimple_phi_arg_def (p, i)) == SSA_NAME)
+	      if (gassign *a = dyn_cast <gassign *> (SSA_NAME_DEF_STMT (use)))
+		{
+		  if (tree op = gimple_assign_rhs1 (a))
+		    if (TREE_CODE (op) == ADDR_EXPR)
+		      visit (a, TREE_OPERAND (op, 0), op, work);
+		}
+	}
     }
 }
 
-- 
2.35.3

Re: [PATCH] middle-end/111422 - wrong stack var coalescing, handle PHIs

[Jakub Jelinek]

On Wed, May 15, 2024 at 01:41:04PM +0200, Richard Biener wrote:
> 	PR middle-end/111422
> 	* cfgexpand.cc (add_scope_conflicts_2): Handle PHIs
> 	by recursing to their arguments.
> ---
>  gcc/cfgexpand.cc | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/gcc/cfgexpand.cc b/gcc/cfgexpand.cc
> index 557cb28733b..e4d763fa998 100644
> --- a/gcc/cfgexpand.cc
> +++ b/gcc/cfgexpand.cc
> @@ -584,10 +584,23 @@ add_scope_conflicts_2 (tree use, bitmap work,
>  	  || INTEGRAL_TYPE_P (TREE_TYPE (use))))
>      {
>        gimple *g = SSA_NAME_DEF_STMT (use);
> -      if (is_gimple_assign (g))
> -	if (tree op = gimple_assign_rhs1 (g))
> -	  if (TREE_CODE (op) == ADDR_EXPR)
> -	    visit (g, TREE_OPERAND (op, 0), op, work);
> +      if (gassign *a = dyn_cast <gassign *> (g))
> +	{
> +	  if (tree op = gimple_assign_rhs1 (a))
> +	    if (TREE_CODE (op) == ADDR_EXPR)
> +	      visit (a, TREE_OPERAND (op, 0), op, work);
> +	}
> +      else if (gphi *p = dyn_cast <gphi *> (g))
> +	{
> +	  for (unsigned i = 0; i < gimple_phi_num_args (p); ++i)
> +	    if (TREE_CODE (use = gimple_phi_arg_def (p, i)) == SSA_NAME)
> +	      if (gassign *a = dyn_cast <gassign *> (SSA_NAME_DEF_STMT (use)))
> +		{
> +		  if (tree op = gimple_assign_rhs1 (a))
> +		    if (TREE_CODE (op) == ADDR_EXPR)
> +		      visit (a, TREE_OPERAND (op, 0), op, work);
> +		}
> +	}

Why the 2 {} pairs here?  Can't it be done without them (sure, before the
else if it is required)?

Otherwise LGTM.

	Jakub

Re: [PATCH] middle-end/111422 - wrong stack var coalescing, handle PHIs

[Richard Biener]

On Wed, 15 May 2024, Jakub Jelinek wrote:

> On Wed, May 15, 2024 at 01:41:04PM +0200, Richard Biener wrote:
> > 	PR middle-end/111422
> > 	* cfgexpand.cc (add_scope_conflicts_2): Handle PHIs
> > 	by recursing to their arguments.
> > ---
> >  gcc/cfgexpand.cc | 21 +++++++++++++++++----
> >  1 file changed, 17 insertions(+), 4 deletions(-)
> > 
> > diff --git a/gcc/cfgexpand.cc b/gcc/cfgexpand.cc
> > index 557cb28733b..e4d763fa998 100644
> > --- a/gcc/cfgexpand.cc
> > +++ b/gcc/cfgexpand.cc
> > @@ -584,10 +584,23 @@ add_scope_conflicts_2 (tree use, bitmap work,
> >  	  || INTEGRAL_TYPE_P (TREE_TYPE (use))))
> >      {
> >        gimple *g = SSA_NAME_DEF_STMT (use);
> > -      if (is_gimple_assign (g))
> > -	if (tree op = gimple_assign_rhs1 (g))
> > -	  if (TREE_CODE (op) == ADDR_EXPR)
> > -	    visit (g, TREE_OPERAND (op, 0), op, work);
> > +      if (gassign *a = dyn_cast <gassign *> (g))
> > +	{
> > +	  if (tree op = gimple_assign_rhs1 (a))
> > +	    if (TREE_CODE (op) == ADDR_EXPR)
> > +	      visit (a, TREE_OPERAND (op, 0), op, work);
> > +	}
> > +      else if (gphi *p = dyn_cast <gphi *> (g))
> > +	{
> > +	  for (unsigned i = 0; i < gimple_phi_num_args (p); ++i)
> > +	    if (TREE_CODE (use = gimple_phi_arg_def (p, i)) == SSA_NAME)
> > +	      if (gassign *a = dyn_cast <gassign *> (SSA_NAME_DEF_STMT (use)))
> > +		{
> > +		  if (tree op = gimple_assign_rhs1 (a))
> > +		    if (TREE_CODE (op) == ADDR_EXPR)
> > +		      visit (a, TREE_OPERAND (op, 0), op, work);
> > +		}
> > +	}
> 
> Why the 2 {} pairs here?  Can't it be done without them (sure, before the
> else if it is required)?

Removed and pushed.

Richard.