Add name canonicalization for C

PR symtab/29105 shows a number of situations where symbol lookup can
result in the expansion of too many CUs.

What happens is that lookup_signed_typename will try to look up a type
like "signed int".  In cooked_index_functions::expand_symtabs_matching,
when looping over languages, the C++ case will canonicalize this type
name to be "int" instead.  Then this method will proceed to expand
every CU that has an entry for "int" -- i.e., nearly all of them.  A
crucial component of this is that the caller, objfile::lookup_symbol,
does not do this canonicalization, so when it tries to find the symbol
for "signed int", it fails -- causing the loop to continue.

This patch fixes the problem by introducing name canonicalization for
C.  The idea here is that, by making C and C++ agree on the canonical
name when a symbol name can have multiple spellings, we avoid the bad
behavior in objfile::lookup_symbol (and any other such code -- I don't
know if there is any).

Unlike C++, C only has a few situations where canonicalization is
needed.  And, in particular, due to the lack of overloading (thus
avoiding any issues in linespec) and due to the way c-exp.y works, I
think that no canonicalization is needed during symbol lookup -- only
during symtab construction.  This explains why lookup_name_info is not
touched.

The stabs reader is modified on a "best effort" basis.

The DWARF reader needed one small tweak in dwarf2_name to avoid a
regression in dw2-unusual-field-names.exp.  I think this is adequately
explained by the comment, but basically this is a scenario that should
not occur in real code, only the gdb test suite.

lookup_signed_typename is simplified.  It used to search for two
different type names, but now gdb can search just for the canonical
form.

gdb.dwarf2/enum-type.exp needed a small tweak, because the
canonicalizer turns "unsigned integer" into "unsigned int integer".
It seems better here to use the correct C type name.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29105
Tested-by: Simon Marchi <simark@simark.ca>
Reviewed-by: Andrew Burgess <aburgess@redhat.com>

2 files changed, 23 insertions, 3 deletions

diff --git a/gdb/dwarf2/cooked-index.c b/gdb/dwarf2/cooked-index.c
index a580d549d0d..0aa026c7779 100644
--- a/gdb/dwarf2/cooked-index.c
+++ b/gdb/dwarf2/cooked-index.c
@@ -21,6 +21,7 @@
 #include "dwarf2/cooked-index.h"
 #include "dwarf2/read.h"
 #include "cp-support.h"
+#include "c-lang.h"
 #include "ada-lang.h"
 #include "split-name.h"
 #include <algorithm>
@@ -210,14 +211,17 @@ cooked_index::do_finalize ()
 	      m_names.push_back (std::move (canon_name));
 	    }
 	}
-      else if (entry->per_cu->lang () == language_cplus)
+      else if (entry->per_cu->lang () == language_cplus
+	       || entry->per_cu->lang () == language_c)
 	{
 	  void **slot = htab_find_slot (seen_names.get (), entry,
 					INSERT);
 	  if (*slot == nullptr)
 	    {
 	      gdb::unique_xmalloc_ptr<char> canon_name
-		= cp_canonicalize_string (entry->name);
+		= (entry->per_cu->lang () == language_cplus
+		   ? cp_canonicalize_string (entry->name)
+		   : c_canonicalize_name (entry->name));
 	      if (canon_name == nullptr)
 		entry->canonical = entry->name;
 	      else
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index aa13d42ad77..032e20af93a 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -22014,7 +22014,10 @@ static const char *
 dwarf2_canonicalize_name (const char *name, struct dwarf2_cu *cu,
 			  struct objfile *objfile)
 {
-  if (name && cu->lang () == language_cplus)
+  if (name == nullptr)
+    return name;
+
+  if (cu->lang () == language_cplus)
     {
       gdb::unique_xmalloc_ptr<char> canon_name
 	= cp_canonicalize_string (name);
@@ -22022,6 +22025,14 @@ dwarf2_canonicalize_name (const char *name, struct dwarf2_cu *cu,
       if (canon_name != nullptr)
 	name = objfile->intern (canon_name.get ());
     }
+  else if (cu->lang () == language_c)
+    {
+      gdb::unique_xmalloc_ptr<char> canon_name
+	= c_canonicalize_name (name);
+
+      if (canon_name != nullptr)
+	name = objfile->intern (canon_name.get ());
+    }
 
   return name;
 }
@@ -22050,6 +22061,11 @@ dwarf2_name (struct die_info *die, struct dwarf2_cu *cu)
 
   switch (die->tag)
     {
+      /* A member's name should not be canonicalized.  This is a bit
+	 of a hack, in that normally it should not be possible to run
+	 into this situation; however, the dw2-unusual-field-names.exp
+	 test creates custom DWARF that does.  */
+    case DW_TAG_member:
     case DW_TAG_compile_unit:
     case DW_TAG_partial_unit:
       /* Compilation units have a DW_AT_name that is a filename, not