Re: [PATCH] c++: non-dependent .* folding [PR112427]

[Patrick Palka <ppalka@redhat.com>]

On Fri, 10 Nov 2023, Jason Merrill wrote:

> On 11/10/23 10:28, Patrick Palka wrote:
> > On Fri, 10 Nov 2023, Patrick Palka wrote:
> > 
> > > On Thu, 9 Nov 2023, Jason Merrill wrote:
> > > 
> > > > On 11/8/23 16:59, Patrick Palka wrote:
> > > > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
> > > > > for
> > > > > trunk?
> > > > > 
> > > > > -- >8 --
> > > > > 
> > > > > Here when building up the non-dependent .* expression, we crash from
> > > > > fold_convert on 'b.a' due to this (templated) COMPONENT_REF having an
> > > > > IDENTIFIER_NODE instead of FIELD_DECL operand that middle-end routines
> > > > > expect.  Like in r14-4899-gd80a26cca02587, this patch fixes this by
> > > > > replacing the problematic piecemeal folding with a single call to
> > > > > cp_fully_fold.
> > > > > 
> > > > > 	PR c++/112427
> > > > > 
> > > > > gcc/cp/ChangeLog:
> > > > > 
> > > > > 	* typeck2.cc (build_m_component_ref): Use cp_convert, build2
> > > > > and
> > > > > 	cp_fully_fold instead of fold_build_pointer_plus and
> > > > > fold_convert.
> > > > 
> > > > > gcc/testsuite/ChangeLog:
> > > > > 
> > > > > 	* g++.dg/template/non-dependent29.C: New test.
> > > > > ---
> > > > >    gcc/cp/typeck2.cc                               |  5 ++++-
> > > > >    gcc/testsuite/g++.dg/template/non-dependent29.C | 13 +++++++++++++
> > > > >    2 files changed, 17 insertions(+), 1 deletion(-)
> > > > >    create mode 100644 gcc/testsuite/g++.dg/template/non-dependent29.C
> > > > > 
> > > > > diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
> > > > > index 309903afed8..208004221da 100644
> > > > > --- a/gcc/cp/typeck2.cc
> > > > > +++ b/gcc/cp/typeck2.cc
> > > > > @@ -2378,7 +2378,10 @@ build_m_component_ref (tree datum, tree
> > > > > component,
> > > > > tsubst_flags_t complain)
> > > > >          /* Build an expression for "object + offset" where offset is
> > > > > the
> > > > >    	 value stored in the pointer-to-data-member.  */
> > > > >          ptype = build_pointer_type (type);
> > > > > -      datum = fold_build_pointer_plus (fold_convert (ptype, datum),
> > > > > component);
> > > > > +      datum = cp_convert (ptype, datum, complain);
> > > > > +      datum = build2 (POINTER_PLUS_EXPR, ptype,
> > > > > +		      datum, convert_to_ptrofftype (component));
> > > > 
> > > > We shouldn't need to build the POINTER_PLUS_EXPR at all in template
> > > > context.
> > > > OK with that change.
> > > 
> > > Hmm, that seems harmless at first glance, but I noticed
> > > build_min_non_dep (called from build_x_binary_op in this case) is
> > > careful to propagate TREE_SIDE_EFFECTS of the given tree, and so eliding
> > > POINTER_PLUS_EXPR here could potentially mean that the tree we
> > > ultimately return from build_x_binary_op when in a template context has
> > > TREE_SIDE_EFFECTS not set when it used to.  Shall we still elide the
> > > POINTER_PLUS_EXPR in a template context despite this?
> 
> True, we would need build_min_non_dep to also get TREE_SIDE_EFFECTS from the
> operands.  That might be useful in general for similar situations?
> 
> I also note that convert_to_ptrofftype uses fold_convert, so the new code
> could have the same problem if the pointer to member operand is also a
> COMPONENT_REF.

Ah, makes sense...  How does the following look then?  I'm not sure if
we still want to replace fold_build_pointer_plus with build2 if we're
not going to use that code path in a template context?  Bootstrapped and
regtested on x86_64-pc-linux-gnu.

-- >8 --
-
Subject: [PATCH] c++: non-dependent .* operand folding [PR112427]

Here when building up the non-dependent .* expression, we crash from
fold_convert on 'b.a' due to this (templated) COMPONENT_REF having an
IDENTIFIER_NODE instead of FIELD_DECL operand that middle-end routines
expect.  Like in r14-4899-gd80a26cca02587, this patch fixes this by
replacing the problematic piecemeal folding with a single call to
cp_fully_fold.  Additionally, don't bother building POINTER_PLUS_EXPR
in a template context.  This means the returned non-dependent tree might
not have TREE_SIDE_EFFECTS set when it used to, so we need to make
build_min_non_dep compensate for this by propagating TREE_SIDE_EFFECTS
from the original arguments like buildN and build_min do, which seems
like a generally desirable thing to do anyway.

	PR c++/112427

gcc/cp/ChangeLog:

	* tree.cc (build_min_non_dep): Propagate TREE_SIDE_EFFECTS from
	the original arguments.
	(build_min_non_dep_call_vec): Likewise.
	* typeck2.cc (build_m_component_ref): Use cp_convert, build2 and
	cp_fully_fold instead of fold_build_pointer_plus and fold_convert.

gcc/testsuite/ChangeLog:

	* g++.dg/template/non-dependent29.C: New test.
---
 gcc/cp/tree.cc                                  | 11 ++++++++++-
 gcc/cp/typeck2.cc                               |  6 +++++-
 gcc/testsuite/g++.dg/template/non-dependent29.C | 13 +++++++++++++
 3 files changed, 28 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/template/non-dependent29.C

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 417c92ba76f..dc4126f935c 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -3601,7 +3601,12 @@ build_min_non_dep (enum tree_code code, tree non_dep, ...)
   TREE_SIDE_EFFECTS (t) = TREE_SIDE_EFFECTS (non_dep);
 
   for (i = 0; i < length; i++)
-    TREE_OPERAND (t, i) = va_arg (p, tree);
+    {
+      tree x = va_arg (p, tree);
+      TREE_OPERAND (t, i) = x;
+      if (x && !TYPE_P (x))
+	TREE_SIDE_EFFECTS (t) |= TREE_SIDE_EFFECTS (x);
+    }
 
   va_end (p);
   return convert_from_reference (t);
@@ -3636,6 +3641,10 @@ build_min_non_dep_call_vec (tree non_dep, tree fn, vec<tree, va_gc> *argvec)
     non_dep = TREE_OPERAND (non_dep, 0);
   TREE_TYPE (t) = TREE_TYPE (non_dep);
   TREE_SIDE_EFFECTS (t) = TREE_SIDE_EFFECTS (non_dep);
+  if (argvec)
+    for (tree x : *argvec)
+      if (x && !TYPE_P (x))
+	TREE_SIDE_EFFECTS (t) |= TREE_SIDE_EFFECTS (x);
   return convert_from_reference (t);
 }
 
diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
index 309903afed8..a75f4f8c2d2 100644
--- a/gcc/cp/typeck2.cc
+++ b/gcc/cp/typeck2.cc
@@ -2378,7 +2378,11 @@ build_m_component_ref (tree datum, tree component, tsubst_flags_t complain)
       /* Build an expression for "object + offset" where offset is the
 	 value stored in the pointer-to-data-member.  */
       ptype = build_pointer_type (type);
-      datum = fold_build_pointer_plus (fold_convert (ptype, datum), component);
+      datum = cp_convert (ptype, datum, complain);
+      if (!processing_template_decl)
+	datum = build2 (POINTER_PLUS_EXPR, ptype,
+			datum, convert_to_ptrofftype (component));
+      datum = cp_fully_fold (datum);
       datum = cp_build_fold_indirect_ref (datum);
       if (datum == error_mark_node)
 	return error_mark_node;
diff --git a/gcc/testsuite/g++.dg/template/non-dependent29.C b/gcc/testsuite/g++.dg/template/non-dependent29.C
new file mode 100644
index 00000000000..41bd11ae6b4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent29.C
@@ -0,0 +1,13 @@
+// PR c++/112427
+
+struct A { int m; void f(); };
+struct B { A a; };
+
+template<class T>
+void f(B b) {
+  int A::*pd = &A::m;
+  b.a.*pd;
+
+  void (A::*pf)() = &A::f;
+  (b.a.*pf)();
+}
-- 
2.43.0.rc1