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, 3 insertions, 9 deletions

diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index 5e8a486d28f..2166257f71e 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -1729,15 +1729,9 @@ lookup_unsigned_typename (const struct language_defn *language,
 struct type *
 lookup_signed_typename (const struct language_defn *language, const char *name)
 {
-  struct type *t;
-  char *uns = (char *) alloca (strlen (name) + 8);
-
-  strcpy (uns, "signed ");
-  strcpy (uns + 7, name);
-  t = lookup_typename (language, uns, NULL, 1);
-  /* If we don't find "signed FOO" just try again with plain "FOO".  */
-  if (t != NULL)
-    return t;
+  /* In C and C++, "char" and "signed char" are distinct types.  */
+  if (streq (name, "char"))
+    name = "signed char";
   return lookup_typename (language, name, NULL, 0);
 }