[gcc r12-7720] c-family: Fix up ICE during pretty-printing of PMF related expression [PR101515]

[gcc r12-7720] c-family: Fix up ICE during pretty-printing of PMF related expression [PR101515]

[Jakub Jelinek]

https://gcc.gnu.org/g:2663d18356b0a62f5a800c7e5596d814cd3c2c41

commit r12-7720-g2663d18356b0a62f5a800c7e5596d814cd3c2c41
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Mar 19 08:40:47 2022 +0100

    c-family: Fix up ICE during pretty-printing of PMF related expression [PR101515]
    
    The intent of r11-6729 is that it prints something that helps user to figure
    out what exactly is being accessed.
    When we find a unique non-static data member that is being accessed, even
    when we can't fold it nicely, IMNSHO it is better to print
      ((sometype *)&var)->field
    or
      (*(sometype *)&var).field
    instead of
      *(fieldtype *)((char *)&var + 56)
    because the user doesn't know what is at offset 56, we shouldn't ask user
    to decipher structure layout etc.
    
    One question is if we could return something better for the TYPE_PTRMEMFUNC_FLAG
    RECORD_TYPE members here (something that would print it more naturally/readably
    in a C++ way), though the fact that the routine is in c-family makes it
    harder.
    
    Another one is whether we shouldn't punt for FIELD_DECLs that don't have
    nicely printable name of its containing scope, something like:
                    if (tree scope = get_containing_scope (field))
                      if (TYPE_P (scope) && TYPE_NAME (scope) == NULL_TREE)
                        break;
                    return cop;
    or so.  This patch implements that.
    
    Note the returned cop is a COMPONENT_REF where the first argument has a
    nicely printable type name (x with type sp), but sp's TYPE_MAIN_VARIANT
    is the unnamed TYPE_PTRMEMFUNC_FLAG.  So another possibility would be if
    we see such a problem for the FIELD_DECL's scope, check if TYPE_MAIN_VARIANT
    of the first COMPONENT_REF's argument is equal to that scope and in that
    case use TREE_TYPE of the first COMPONENT_REF's argument as the scope
    instead.
    
    2022-03-19  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/101515
            * c-pretty-print.cc (c_fold_indirect_ref_for_warn): For C++ don't
            return COMPONENT_REFs with FIELD_DECLs whose containing scope can't
            be printed.
    
            * g++.dg/warn/pr101515.C: New test.

Diff:
---
 gcc/c-family/c-pretty-print.cc       |  6 ++++++
 gcc/testsuite/g++.dg/warn/pr101515.C | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/gcc/c-family/c-pretty-print.cc b/gcc/c-family/c-pretty-print.cc
index dac17753acb..71a0cb51093 100644
--- a/gcc/c-family/c-pretty-print.cc
+++ b/gcc/c-family/c-pretty-print.cc
@@ -1889,6 +1889,12 @@ c_fold_indirect_ref_for_warn (location_t loc, tree type, tree op,
 	      = wi::to_offset (TYPE_SIZE_UNIT (TREE_TYPE (field)));
 	    if (upos <= off && off < upos + el_sz)
 	      {
+		/* The C++ pretty printers print scope of the FIELD_DECLs,
+		   so punt if it is something that can't be printed.  */
+		if (c_dialect_cxx ())
+		  if (tree scope = get_containing_scope (field))
+		    if (TYPE_P (scope) && TYPE_NAME (scope) == NULL_TREE)
+		      break;
 		tree cop = build3_loc (loc, COMPONENT_REF, TREE_TYPE (field),
 				       op, field, NULL_TREE);
 		off = off - upos;
diff --git a/gcc/testsuite/g++.dg/warn/pr101515.C b/gcc/testsuite/g++.dg/warn/pr101515.C
new file mode 100644
index 00000000000..f3c58b89094
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/pr101515.C
@@ -0,0 +1,18 @@
+// PR c++/101515
+// { dg-do compile }
+// { dg-options "-O1 -Wuninitialized" }
+
+struct S { int j; };
+struct T : public S { virtual void h () {} };
+struct U { void (*ptr) (); };
+typedef void (S::*sp) ();
+
+int
+main ()
+{
+  T t;
+  sp x;
+  U *xp = (U *) &x;
+  if (xp->ptr != ((void (*) ()) (sizeof (void *))))	// { dg-warning "is used uninitialized" }
+    return 1;
+}