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>

1 files changed, 13 insertions, 0 deletions

diff --git a/gdb/dbxread.c b/gdb/dbxread.c
index b0047cf..ae726bd 100644
--- a/gdb/dbxread.c
+++ b/gdb/dbxread.c
@@ -48,6 +48,7 @@
 #include "complaints.h"
 #include "cp-abi.h"
 #include "cp-support.h"
+#include "c-lang.h"
 #include "psympriv.h"
 #include "block.h"
 #include "aout/aout64.h"
@@ -1444,6 +1445,18 @@ read_dbx_symtab (minimal_symbol_reader &reader,
 					     new_name.get ());
 		}
 	    }
+	  else if (psymtab_language == language_c)
+	    {
+	      std::string name (namestring, p - namestring);
+	      gdb::unique_xmalloc_ptr<char> new_name
+		= c_canonicalize_name (name.c_str ());
+	      if (new_name != nullptr)
+		{
+		  sym_len = strlen (new_name.get ());
+		  sym_name = obstack_strdup (&objfile->objfile_obstack,
+					     new_name.get ());
+		}
+	    }
 
 	  if (sym_len == 0)
 	    {