analyzer: don't print the duplicate count by default

The note about duplicates attached to analyzer diagnostics feels like an
implementation detail; it's likely just noise from the perspective of an
end-user.

This patch disables it by default, introducing a flag to re-enable it.

gcc/analyzer/ChangeLog:
	* analyzer.opt (fanalyzer-show-duplicate-count): New option.
	* diagnostic-manager.cc
	(diagnostic_manager::emit_saved_diagnostic): Use the above to
	guard the printing of the duplicate count.

gcc/ChangeLog:
	* doc/invoke.texi (-fanalyzer-show-duplicate-count): New.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/CVE-2005-1689-dedupe-issue.c: Add
	-fanalyzer-show-duplicate-count.

gcc/ChangeLog

 2020-03-02  David Malcolm  <dmalcolm@redhat.com>
 
+	* doc/invoke.texi (-fanalyzer-show-duplicate-count): New.
+
+2020-03-02  David Malcolm  <dmalcolm@redhat.com>
+
 	* doc/invoke.texi (Static Analyzer Options): Add
 	-Wanalyzer-stale-setjmp-buffer to the list of options enabled
 	by -fanalyzer.

gcc/analyzer/ChangeLog

 2020-03-02  David Malcolm  <dmalcolm@redhat.com>
 
+	* analyzer.opt (fanalyzer-show-duplicate-count): New option.
+	* diagnostic-manager.cc
+	(diagnostic_manager::emit_saved_diagnostic): Use the above to
+	guard the printing of the duplicate count.
+
+2020-03-02  David Malcolm  <dmalcolm@redhat.com>
+
 	PR analyzer/93959
 	* analyzer.cc (is_std_function_p): New function.
 	(is_std_named_call_p): New functions.

gcc/analyzer/analyzer.opt

@@ -114,6 +114,10 @@ fanalyzer-fine-grained
 Common Var(flag_analyzer_fine_grained) Init(0)
 Avoid combining multiple statements into one exploded edge.
 
+fanalyzer-show-duplicate-count
+Common Var(flag_analyzer_show_duplicate_count) Init(0)
+Issue a note when diagnostics are deduplicated.
+
 fanalyzer-state-purge
 Common Var(flag_analyzer_state_purge) Init(1)
 Purge unneeded state during analysis.

gcc/analyzer/diagnostic-manager.cc

@@ -541,7 +541,7 @@ diagnostic_manager::emit_saved_diagnostic (const exploded_graph &eg,
   auto_cfun sentinel (sd.m_snode->m_fun);
   if (sd.m_d->emit (&rich_loc))
     {
-      if (num_dupes > 0)
+      if (flag_analyzer_show_duplicate_count && num_dupes > 0)
 	inform_n (stmt->location, num_dupes,
 		  "%i duplicate", "%i duplicates",
 		  num_dupes);

gcc/doc/invoke.texi

@@ -8477,6 +8477,14 @@ By default, an edge in this graph can contain the effects of a run
 of multiple statements within a basic block.  With
 @option{-fanalyzer-fine-grained}, each statement gets its own edge.
 
+@item -fanalyzer-show-duplicate-count
+@opindex fanalyzer-show-duplicate-count
+@opindex fno-analyzer-show-duplicate-count
+This option is intended for analyzer developers: if multiple diagnostics
+have been detected as being duplicates of each other, it emits a note when
+reporting the best diagnostic, giving the number of additional diagnostics
+that were suppressed by the deduplication logic.
+
 @item -fno-analyzer-state-merge
 @opindex fanalyzer-state-merge
 @opindex fno-analyzer-state-merge

gcc/testsuite/ChangeLog

 2020-03-02  David Malcolm  <dmalcolm@redhat.com>
 
+	* gcc.dg/analyzer/CVE-2005-1689-dedupe-issue.c: Add
+	-fanalyzer-show-duplicate-count.
+
+2020-03-02  David Malcolm  <dmalcolm@redhat.com>
+
 	PR analyzer/93959
 	* g++.dg/analyzer/cstdlib-2.C: New test.
 	* g++.dg/analyzer/cstdlib.C: New test.

gcc/testsuite/gcc.dg/analyzer/CVE-2005-1689-dedupe-issue.c

+/* { dg-additional-options "-fanalyzer-show-duplicate-count" } */
+
 #include <stdlib.h>
 
 typedef struct _krb5_data {