Re: [PATCH] lto: Fix up lto_fixup_prevailing_type [PR108910]

[Jakub Jelinek <jakub@redhat.com>]

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On Tue, Feb 28, 2023 at 09:43:37AM +0000, Richard Biener wrote:
> We try to make sure to put all built types into the type merging
> machinery, so I think it shouldn't happen - but then I cannot rule
> it out.  I'm also not sure whether duplicates would really pose
> a problem here (other than waste).  If we want to make sure we should
> probably enhance verify_types to verify the TYPE_POINTER_TO chain ...
> 
> > I'll try to debug why those user aligned types become TYPE_MAIN_VARIANT
> > though...

Ok, so this happens already in the FEs when trying to add the attribute:
#0  build_distinct_type_copy (type=<pointer_type 0x7fffea0219d8>) at ../../gcc/tree.cc:5735
#1  0x0000000000c2327b in build_type_attribute_qual_variant (otype=<pointer_type 0x7fffea0219d8>, attribute=<tree_list 0x7fffea01e938>, quals=0) at ../../gcc/attribs.cc:1298
#2  0x0000000000c245b0 in build_type_attribute_variant (ttype=<pointer_type 0x7fffea0219d8>, attribute=<tree_list 0x7fffea01e938>) at ../../gcc/attribs.cc:1591
#3  0x0000000000c22325 in decl_attributes (node=0x7fffffffd008, attributes=<tree_list 0x7fffea01e910>, flags=1, last_decl=<tree 0x0>) at ../../gcc/attribs.cc:964

So, perhaps the !TYPE_QUALS (t) could be just an assert, but maybe next to
the !TYPE_USER_ALIGN (t) (or just instead of?) we need !TYPE_ATTRIBUTES (t).
Because addition of attributes (but anything else that causes
build_distinct_type_copy rather than build_variant_type_copy) will create
new TYPE_MAIN_VARIANTS.
Looking around, TYPE_REF_IS_RVALUE references also create distinct types,
and while the C++ FE sticks them into the TYPE_REFERENCE_TO chain, it
ensures they go after the corresponding !TYPE_REF_IS_RVALUE entry, so
perhaps LTO should !TYPE_REF_IS_RVALUE for REFERENCE_TYPEs.
Other uses of build_distinct_type_copy in the FEs are mostly related to
ARRAY_TYPEs (in C FE as well as c-common).  Asan uses it solely on integral
types, etc.  For attributes, big question is if it when we set
*no_addr_attrs = true we still tweak some things on the type (not in place)
or not.

So, here are two possible variant patches which fix the ICE on the
testcase too.

2023-02-28  Jakub Jelinek  <jakub@redhat.com>

	PR target/108910
	* lto-common.cc (lto_fixup_prevailing_type): Don't add t to
	TYPE_POINTER_TO or TYPE_REFERENCE_TO chain if it has 
	TYPE_ATTRIBUTES, or is TYPE_REF_IS_RVALUE, or some other type
	with the same TYPE_MODE and TYPE_REF_CAN_ALIAS_ALL flag is already
	present.

--- gcc/lto/lto-common.cc.jj	2023-01-16 11:52:16.165732856 +0100
+++ gcc/lto/lto-common.cc	2023-02-28 12:30:37.014471255 +0100
@@ -984,21 +984,36 @@ lto_fixup_prevailing_type (tree t)
       TYPE_NEXT_VARIANT (t) = TYPE_NEXT_VARIANT (mv);
       TYPE_NEXT_VARIANT (mv) = t;
     }
-
-  /* The following reconstructs the pointer chains
-     of the new pointed-to type if we are a main variant.  We do
-     not stream those so they are broken before fixup.  */
-  if (TREE_CODE (t) == POINTER_TYPE
-      && TYPE_MAIN_VARIANT (t) == t)
-    {
-      TYPE_NEXT_PTR_TO (t) = TYPE_POINTER_TO (TREE_TYPE (t));
-      TYPE_POINTER_TO (TREE_TYPE (t)) = t;
-    }
-  else if (TREE_CODE (t) == REFERENCE_TYPE
-	   && TYPE_MAIN_VARIANT (t) == t)
+  else if (!TYPE_ATTRIBUTES (t))
     {
-      TYPE_NEXT_REF_TO (t) = TYPE_REFERENCE_TO (TREE_TYPE (t));
-      TYPE_REFERENCE_TO (TREE_TYPE (t)) = t;
+      /* The following reconstructs the pointer chains
+	 of the new pointed-to type if we are a main variant.  We do
+	 not stream those so they are broken before fixup.
+	 Don't add it if despite being main variant it has
+	 attributes (then it was created with build_distinct_type_copy).
+	 Similarly don't add TYPE_REF_IS_RVALUE REFERENCE_TYPEs.
+	 Don't add it if there is something in the chain already.  */
+      tree *p = NULL;
+      if (TREE_CODE (t) == POINTER_TYPE)
+	p = &TYPE_POINTER_TO (TREE_TYPE (t));
+      else if (TREE_CODE (t) == REFERENCE_TYPE && !TYPE_REF_IS_RVALUE (t))
+	p = &TYPE_REFERENCE_TO (TREE_TYPE (t));
+      if (p)
+	{
+	  tree t2;
+	  for (t2 = *p; t2; t2 = TYPE_NEXT_PTR_TO (t2))
+	    if (TYPE_MODE (t2) == TYPE_MODE (t)
+		&& TYPE_REF_CAN_ALIAS_ALL (t2) == TYPE_REF_CAN_ALIAS_ALL (t))
+	      break;
+	  if (t2 == NULL_TREE)
+	    {
+	      if (TREE_CODE (t) == POINTER_TYPE)
+		TYPE_NEXT_PTR_TO (t) = *p;
+	      else
+		TYPE_NEXT_REF_TO (t) = *p;
+	      *p = t;
+	    }
+	}
     }
 }
 


	Jakub

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2023-02-28  Jakub Jelinek  <jakub@redhat.com>

	PR target/108910
	* lto-common.cc (lto_fixup_prevailing_type): Don't add t to
	TYPE_POINTER_TO or TYPE_REFERENCE_TO chain if it has 
	TYPE_ATTRIBUTES or is TYPE_REF_IS_RVALUE.

--- gcc/lto/lto-common.cc.jj	2023-01-16 11:52:16.165732856 +0100
+++ gcc/lto/lto-common.cc	2023-02-28 12:34:33.698038478 +0100
@@ -984,21 +984,25 @@ lto_fixup_prevailing_type (tree t)
       TYPE_NEXT_VARIANT (t) = TYPE_NEXT_VARIANT (mv);
       TYPE_NEXT_VARIANT (mv) = t;
     }
-
-  /* The following reconstructs the pointer chains
-     of the new pointed-to type if we are a main variant.  We do
-     not stream those so they are broken before fixup.  */
-  if (TREE_CODE (t) == POINTER_TYPE
-      && TYPE_MAIN_VARIANT (t) == t)
-    {
-      TYPE_NEXT_PTR_TO (t) = TYPE_POINTER_TO (TREE_TYPE (t));
-      TYPE_POINTER_TO (TREE_TYPE (t)) = t;
-    }
-  else if (TREE_CODE (t) == REFERENCE_TYPE
-	   && TYPE_MAIN_VARIANT (t) == t)
+  else if (!TYPE_ATTRIBUTES (t))
     {
-      TYPE_NEXT_REF_TO (t) = TYPE_REFERENCE_TO (TREE_TYPE (t));
-      TYPE_REFERENCE_TO (TREE_TYPE (t)) = t;
+      /* The following reconstructs the pointer chains
+	 of the new pointed-to type if we are a main variant.  We do
+	 not stream those so they are broken before fixup.
+	 Don't add it if despite being main variant it has
+	 attributes (then it was created with build_distinct_type_copy).
+	 Similarly don't add TYPE_REF_IS_RVALUE REFERENCE_TYPEs.
+	 Don't add it if there is something in the chain already.  */
+      if (TREE_CODE (t) == POINTER_TYPE)
+	{
+	  TYPE_NEXT_PTR_TO (t) = TYPE_POINTER_TO (TREE_TYPE (t));
+	  TYPE_POINTER_TO (TREE_TYPE (t)) = t;
+	}
+      else if (TREE_CODE (t) == REFERENCE_TYPE && !TYPE_REF_IS_RVALUE (t))
+	{
+	  TYPE_NEXT_REF_TO (t) = TYPE_REFERENCE_TO (TREE_TYPE (t));
+	  TYPE_REFERENCE_TO (TREE_TYPE (t)) = t;
+	}
     }
 }