Fix TYPE_MAIN_VARIANT construction for arrays of qualified typedefs (PR c/68162).

PR c/68162 reports a spurious warning about incompatible types
involving arrays of const double, constructed in one place using a
typedef for const double and in another place literally using const
double.

The problem is that the array of the typedef was incorrectly
constructed without a TYPE_MAIN_VARIANT being an array of unqualified
elements as it should be (though it seems some more recent change
resulted in this producing incorrect diagnostics, likely the support
for C++-style handling of arrays of qualified type).  This patch fixes
the logic in grokdeclarator to determine first_non_attr_kind, which is
used to determine whether it is necessary to use the TYPE_MAIN_VARIANT
of the type in the declaration specifiers.

However, fixing that logic introduces a failure of
gcc.dg/debug/dwarf2/pr47939-4.c, a test introduced along with
first_non_attr_kind.  Thus, it is necessary to track the original
qualified typedef when qualifying an array type, to use it rather than
a newly-constructed type, to avoid regressing regarding typedef names
in debug info.  This is done along lines I suggested in
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47939#c6>: track the
original type and the number of levels of array indirection at which
it appears, and, in possibly affected cases, pass extra arguments to
c_build_qualified_type (with default arguments to avoid needing to
pass those extra arguments explicitly everywhere).  Given Richard's
recent fix to dwarf2out.c, this allows the C bug to be fixed without
causing debug information regressions.

Bootstrapped with no regressions on x86_64-pc-linux-gnu.

gcc/c:
	PR c/68162
	* c-decl.c (grokdeclarator): Set first_non_attr_kind before
	following link from declarator to next declarator.  Track original
	qualified type and pass it to c_build_qualified_type.
	* c-typeck.c (c_build_qualified_type): Add arguments
	orig_qual_type and orig_qual_indirect.

gcc/c-family:
	PR c/68162
	* c-common.h (c_build_qualified_type): Add extra default
	arguments.

gcc/cp:
	PR c/68162
	* tree.c (c_build_qualified_type): Add extra arguments.

gcc/testsuite:
	PR c/68162
	* gcc.dg/pr68162-1.c: New test.

From-SVN: r231194

1 files changed, 24 insertions, 8 deletions

diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index efb0a52..9ad8219 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -5351,6 +5351,8 @@ grokdeclarator (const struct c_declarator *declarator,
   tree returned_attrs = NULL_TREE;
   bool bitfield = width != NULL;
   tree element_type;
+  tree orig_qual_type = NULL;
+  size_t orig_qual_indirect = 0;
   struct c_arg_info *arg_info = 0;
   addr_space_t as1, as2, address_space;
   location_t loc = UNKNOWN_LOCATION;
@@ -5389,9 +5391,9 @@ grokdeclarator (const struct c_declarator *declarator,
 	case cdk_function:
 	case cdk_pointer:
 	  funcdef_syntax = (decl->kind == cdk_function);
-	  decl = decl->declarator;
 	  if (first_non_attr_kind == cdk_attrs)
 	    first_non_attr_kind = decl->kind;
+	  decl = decl->declarator;
 	  break;
 
 	case cdk_attrs:
@@ -5513,12 +5515,17 @@ grokdeclarator (const struct c_declarator *declarator,
   if ((TREE_CODE (type) == ARRAY_TYPE
        || first_non_attr_kind == cdk_array)
       && TYPE_QUALS (element_type))
-    type = TYPE_MAIN_VARIANT (type);
+    {
+      orig_qual_type = type;
+      type = TYPE_MAIN_VARIANT (type);
+    }
   type_quals = ((constp ? TYPE_QUAL_CONST : 0)
 		| (restrictp ? TYPE_QUAL_RESTRICT : 0)
 		| (volatilep ? TYPE_QUAL_VOLATILE : 0)
 		| (atomicp ? TYPE_QUAL_ATOMIC : 0)
 		| ENCODE_QUAL_ADDR_SPACE (address_space));
+  if (type_quals != TYPE_QUALS (element_type))
+    orig_qual_type = NULL_TREE;
 
   /* Applying the _Atomic qualifier to an array type (through the use
      of typedefs or typeof) must be detected here.  If the qualifier
@@ -6013,6 +6020,7 @@ grokdeclarator (const struct c_declarator *declarator,
 		array_ptr_attrs = NULL_TREE;
 		array_parm_static = 0;
 	      }
+	    orig_qual_indirect++;
 	    break;
 	  }
 	case cdk_function:
@@ -6022,6 +6030,7 @@ grokdeclarator (const struct c_declarator *declarator,
 	       attributes.  */
 	    bool really_funcdef = false;
 	    tree arg_types;
+	    orig_qual_type = NULL_TREE;
 	    if (funcdef_flag)
 	      {
 		const struct c_declarator *t = declarator->declarator;
@@ -6122,7 +6131,9 @@ grokdeclarator (const struct c_declarator *declarator,
 	      pedwarn (loc, OPT_Wpedantic,
 		       "ISO C forbids qualified function types");
 	    if (type_quals)
-	      type = c_build_qualified_type (type, type_quals);
+	      type = c_build_qualified_type (type, type_quals, orig_qual_type,
+					     orig_qual_indirect);
+	    orig_qual_type = NULL_TREE;
 	    size_varies = false;
 
 	    /* When the pointed-to type involves components of variable size,
@@ -6304,7 +6315,8 @@ grokdeclarator (const struct c_declarator *declarator,
 	pedwarn (loc, OPT_Wpedantic,
 		 "ISO C forbids qualified function types");
       if (type_quals)
-	type = c_build_qualified_type (type, type_quals);
+	type = c_build_qualified_type (type, type_quals, orig_qual_type,
+				       orig_qual_indirect);
       decl = build_decl (declarator->id_loc,
 			 TYPE_DECL, declarator->u.id, type);
       if (declspecs->explicit_signed_p)
@@ -6357,7 +6369,8 @@ grokdeclarator (const struct c_declarator *declarator,
 	pedwarn (loc, OPT_Wpedantic,
 		 "ISO C forbids const or volatile function types");
       if (type_quals)
-	type = c_build_qualified_type (type, type_quals);
+	type = c_build_qualified_type (type, type_quals, orig_qual_type,
+				       orig_qual_indirect);
       return type;
     }
 
@@ -6405,7 +6418,8 @@ grokdeclarator (const struct c_declarator *declarator,
 	    /* Transfer const-ness of array into that of type pointed to.  */
 	    type = TREE_TYPE (type);
 	    if (type_quals)
-	      type = c_build_qualified_type (type, type_quals);
+	      type = c_build_qualified_type (type, type_quals, orig_qual_type,
+					     orig_qual_indirect);
 	    type = c_build_pointer_type (type);
 	    type_quals = array_ptr_quals;
 	    if (type_quals)
@@ -6496,7 +6510,8 @@ grokdeclarator (const struct c_declarator *declarator,
 	    TYPE_DOMAIN (type) = build_range_type (sizetype, size_zero_node,
 						   NULL_TREE);
 	  }
-	type = c_build_qualified_type (type, type_quals);
+	type = c_build_qualified_type (type, type_quals, orig_qual_type,
+				       orig_qual_indirect);
 	decl = build_decl (declarator->id_loc,
 			   FIELD_DECL, declarator->u.id, type);
 	DECL_NONADDRESSABLE_P (decl) = bitfield;
@@ -6608,7 +6623,8 @@ grokdeclarator (const struct c_declarator *declarator,
 	/* An uninitialized decl with `extern' is a reference.  */
 	int extern_ref = !initialized && storage_class == csc_extern;
 
-	type = c_build_qualified_type (type, type_quals);
+	type = c_build_qualified_type (type, type_quals, orig_qual_type,
+				       orig_qual_indirect);
 
 	/* C99 6.2.2p7: It is invalid (compile-time undefined
 	   behavior) to create an 'extern' declaration for a