[rtsan] Add option to allow printing of duplicate stacks (suppress_equal_stacks) (#117069)

Following the example of tsan, where we took the name

This would allow users to determine if they want to see ALL output from
rtsan.

Additionally, remove the UNLIKELY hint, as it is now up to the flag whether or
not it is likely that we go through this conditional.

Author: cjappl

compiler-rt/lib/rtsan/rtsan.cpp

@@ -55,11 +55,7 @@ static void OnViolation(const BufferedStackTrace &stack,
   StackDepotHandle handle = StackDepotPut_WithHandle(stack);
 
   const bool is_stack_novel = handle.use_count() == 0;
-
-  // Marked UNLIKELY as if user is runing with halt_on_error=false
-  // we expect a high number of duplicate stacks. We are willing
-  // To pay for the first insertion.
-  if (UNLIKELY(is_stack_novel)) {
+  if (is_stack_novel || !flags().suppress_equal_stacks) {
     IncrementUniqueErrorCount();
 
     {

compiler-rt/lib/rtsan/rtsan_flags.inc

@@ -19,3 +19,6 @@
 RTSAN_FLAG(bool, halt_on_error, true, "Exit after first reported error.")
 RTSAN_FLAG(bool, print_stats_on_exit, false, "Print stats on exit.")
 RTSAN_FLAG(const char *, suppressions, "", "Suppressions file name.")
+RTSAN_FLAG(bool, suppress_equal_stacks, true,
+           "Suppress a report if we've already output another report "
+           "with the same stack.")

compiler-rt/test/rtsan/deduplicate_errors.cpp

@@ -1,5 +1,6 @@
 // RUN: %clangxx -fsanitize=realtime %s -o %t
 // RUN: env RTSAN_OPTIONS="halt_on_error=false,print_stats_on_exit=true" %run %t 2>&1 | FileCheck %s
+// RUN: env RTSAN_OPTIONS="halt_on_error=false,suppress_equal_stacks=false" %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-DUPLICATES
 
 // UNSUPPORTED: ios
 
@@ -37,3 +38,6 @@ int main() {
 // CHECK: RealtimeSanitizer exit stats:
 // CHECK-NEXT: Total error count: 220
 // CHECK-NEXT: Unique error count: 4
+
+// CHECK-DUPLICATES-COUNT-220: ==ERROR:
+// CHECK-DUPLICATES-NOT: ==ERROR: