[Bug tree-optimization/67666] New: single restrict pointer in struct looses restrict

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67666

            Bug ID: 67666
           Summary: single restrict pointer in struct looses restrict
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

Consider testcase test.c:
...
struct ps
{
  int *__restrict__ p;
};

void
f (struct ps &__restrict__ ps1)
{
  *(ps1.p) = 1;
}
...

Compile the test-case with g++ -O2, and we get one clique/base annotation at
ealias (the one for ps1, not the one for p):
...
void f(ps&) (struct psD.2252 & restrict ps1D.2255)
{
  intD.9 * _3;

  # VUSE <.MEM_1(D)>
  # PT = nonlocal escaped 
  _3 = MEM[(struct psD.2252 &)ps1_2(D) clique 1 base 1].pD.2254;

  # .MEM_4 = VDEF <.MEM_1(D)>
  *_3 = 1;
...

After applying the patch:
...
--- test7.c.orig        2015-09-21 11:38:30.607225802 +0200
+++ test7.c     2015-09-21 11:29:40.891234983 +0200
@@ -1,6 +1,7 @@
 struct ps
 {
   int *__restrict__ p;
+  int a;
 };

 void
...

we get both clique/base annotations at ealias:
...
void f(ps&) (struct psD.2252 & restrict ps1D.2256)
{
  intD.9 * _3;

  # VUSE <.MEM_1(D)>
  # PT = { D.2263 } (nonlocal)
  _3 = MEM[(struct psD.2252 &)ps1_2(D) clique 1 base 1].pD.2254;

  # .MEM_4 = VDEF <.MEM_1(D)>
  MEM[(intD.9 *)_3 clique 1 base 2] = 1;
  # VUSE <.MEM_4>
...

Using this demonstrator patch, I manage to get both clique/base annotations at
ealias, without adding an 'int a' field to the struct:
...
diff --git a/gcc/tree-ssa-structalias.c b/gcc/tree-ssa-structalias.c
index b5b9d0a..e99feeb 100644
--- a/gcc/tree-ssa-structalias.c
+++ b/gcc/tree-ssa-structalias.c
@@ -5675,8 +5675,7 @@ create_variable_info_for_1 (tree decl, const char *name)

   /* If we didn't end up collecting sub-variables create a full
      variable for the decl.  */
-  if (fieldstack.length () <= 1
-      || fieldstack.length () > MAX_FIELDS_FOR_FIELD_SENSITIVE)
+  if (fieldstack.length () > MAX_FIELDS_FOR_FIELD_SENSITIVE)
     {
       vi = new_var_info (decl, name);
       vi->offset = 0;
...