[PATCH 3/3] Add name canonicalization for C

[Tom Tromey <tromey@adacore.com>]

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
---
 gdb/c-lang.c                           | 14 ++++++++++++
 gdb/c-lang.h                           |  5 +++++
 gdb/dbxread.c                          | 13 +++++++++++
 gdb/dwarf2/cooked-index.c              |  8 +++++--
 gdb/dwarf2/read.c                      | 18 +++++++++++++++-
 gdb/gdbtypes.c                         | 12 +++--------
 gdb/stabsread.c                        | 30 ++++++++++++++++----------
 gdb/testsuite/gdb.dwarf2/enum-type.exp |  4 ++--
 8 files changed, 79 insertions(+), 25 deletions(-)

diff --git a/gdb/c-lang.c b/gdb/c-lang.c
index 36b4d1ae3dd..bfad7aeee60 100644
--- a/gdb/c-lang.c
+++ b/gdb/c-lang.c
@@ -727,6 +727,20 @@ c_is_string_type_p (struct type *type)
 
 \f
 
+/* See c-lang.h.  */
+
+gdb::unique_xmalloc_ptr<char>
+c_canonicalize_name (const char *name)
+{
+  if (strchr (name, ' ') != nullptr
+      || streq (name, "signed")
+      || streq (name, "unsigned"))
+    return cp_canonicalize_string (name);
+  return nullptr;
+}
+
+\f
+
 void
 c_language_arch_info (struct gdbarch *gdbarch,
 		      struct language_arch_info *lai)
diff --git a/gdb/c-lang.h b/gdb/c-lang.h
index 93515671d80..652f147f656 100644
--- a/gdb/c-lang.h
+++ b/gdb/c-lang.h
@@ -167,4 +167,9 @@ extern std::string cplus_compute_program (compile_instance *inst,
 					  const struct block *expr_block,
 					  CORE_ADDR expr_pc);
 
+/* Return the canonical form of the C symbol NAME.  If NAME is already
+   canonical, return nullptr.  */
+
+extern gdb::unique_xmalloc_ptr<char> c_canonicalize_name (const char *name);
+
 #endif /* !defined (C_LANG_H) */
diff --git a/gdb/dbxread.c b/gdb/dbxread.c
index b0047cf0e79..ae726bdfcc6 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)
 	    {
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 978dd4d0bb9..0826f907800 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -22001,7 +22001,10 @@ 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);
@@ -22009,6 +22012,14 @@ 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;
 }
@@ -22037,6 +22048,11 @@ 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
diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index a43d9265ad2..d6e8109a95c 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -1721,15 +1721,9 @@ 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);
 }
 
diff --git a/gdb/stabsread.c b/gdb/stabsread.c
index 612443557b5..74d0885fa71 100644
--- a/gdb/stabsread.c
+++ b/gdb/stabsread.c
@@ -736,11 +736,13 @@ define_symbol (CORE_ADDR valu, const char *string, int desc, int type,
 
       if (sym->language () == language_cplus)
 	{
-	  char *name = (char *) alloca (p - string + 1);
-
-	  memcpy (name, string, p - string);
-	  name[p - string] = '\0';
-	  new_name = cp_canonicalize_string (name);
+	  std::string name (string, p - string);
+	  new_name = cp_canonicalize_string (name.c_str ());
+	}
+      else if (sym->language () == language_c)
+	{
+	  std::string name (string, p - string);
+	  new_name = c_canonicalize_name (name.c_str ());
 	}
       if (new_name != nullptr)
 	sym->compute_and_set_names (new_name.get (), true, objfile->per_bfd);
@@ -1592,12 +1594,18 @@ read_type (const char **pp, struct objfile *objfile)
 	  type_name = NULL;
 	  if (get_current_subfile ()->language == language_cplus)
 	    {
-	      char *name = (char *) alloca (p - *pp + 1);
-
-	      memcpy (name, *pp, p - *pp);
-	      name[p - *pp] = '\0';
-
-	      gdb::unique_xmalloc_ptr<char> new_name = cp_canonicalize_string (name);
+	      std::string name (*pp, p - *pp);
+	      gdb::unique_xmalloc_ptr<char> new_name
+		= cp_canonicalize_string (name.c_str ());
+	      if (new_name != nullptr)
+		type_name = obstack_strdup (&objfile->objfile_obstack,
+					    new_name.get ());
+	    }
+	  else if (get_current_subfile ()->language == language_c)
+	    {
+	      std::string name (*pp, p - *pp);
+	      gdb::unique_xmalloc_ptr<char> new_name
+		= c_canonicalize_name (name.c_str ());
 	      if (new_name != nullptr)
 		type_name = obstack_strdup (&objfile->objfile_obstack,
 					    new_name.get ());
diff --git a/gdb/testsuite/gdb.dwarf2/enum-type.exp b/gdb/testsuite/gdb.dwarf2/enum-type.exp
index ed8e3a35d69..6ebaefa6fb1 100644
--- a/gdb/testsuite/gdb.dwarf2/enum-type.exp
+++ b/gdb/testsuite/gdb.dwarf2/enum-type.exp
@@ -43,7 +43,7 @@ Dwarf::assemble $asm_file {
             uinteger_label: DW_TAG_base_type {
                 {DW_AT_byte_size 4 DW_FORM_sdata}
                 {DW_AT_encoding  @DW_ATE_unsigned}
-                {DW_AT_name      {unsigned integer}}
+		{DW_AT_name      {unsigned int}}
             }
 
 	    DW_TAG_enumeration_type {
@@ -79,5 +79,5 @@ gdb_test "print sizeof(enum E)" " = 4"
 gdb_test "ptype enum EU" "type = enum EU {TWO = 2}" \
     "ptype EU in enum C"
 gdb_test_no_output "set lang c++"
-gdb_test "ptype enum EU" "type = enum EU : unsigned integer {TWO = 2}" \
+gdb_test "ptype enum EU" "type = enum EU : unsigned int {TWO = 2}" \
     "ptype EU in C++"
-- 
2.34.3