tsan: Add param to disable func-entry-exit instrumentation

Adds param tsan-instrument-func-entry-exit, which controls if
__tsan_func_{entry,exit} calls should be emitted or not. The default
behaviour is to emit the calls.

This may be required by alternative race detection runtimes. One such
runtime is the Kernel Concurrency Sanitizer (KCSAN):

	https://github.com/google/ktsan/wiki/KCSAN

After this change, GCC should satisfy all requirements for KCSAN:

	https://lore.kernel.org/lkml/20200515150338.190344-7-elver@google.com/

gcc/ChangeLog:

	* gimplify.c (gimplify_function_tree): Optimize and do not emit
	IFN_TSAN_FUNC_EXIT in a finally block if we do not need it.
	* params.opt: Add --param=tsan-instrument-func-entry-exit=.
	* tsan.c (instrument_memory_accesses): Make
	fentry_exit_instrument bool depend on new param.

gcc/testsuite/ChangeLog:

	* c-c++-common/tsan/func_entry_exit.c: New test.
	* c-c++-common/tsan/func_entry_exit_disabled.c: New test.

gcc/gimplify.c

@@ -15011,7 +15011,8 @@ gimplify_function_tree (tree fndecl)
       bind = new_bind;
     }
 
-  if (sanitize_flags_p (SANITIZE_THREAD))
+  if (sanitize_flags_p (SANITIZE_THREAD)
+      && param_tsan_instrument_func_entry_exit)
     {
       gcall *call = gimple_build_call_internal (IFN_TSAN_FUNC_EXIT, 0);
       gimple *tf = gimple_build_try (seq, call, GIMPLE_TRY_FINALLY);

gcc/params.opt

@@ -912,6 +912,10 @@ Set the maximum number of instructions executed in parallel in reassociated tree
 Common Joined UInteger Var(param_tsan_distinguish_volatile) IntegerRange(0, 1) Param
 Emit special instrumentation for accesses to volatiles.
 
+-param=tsan-instrument-func-entry-exit=
+Common Joined UInteger Var(param_tsan_instrument_func_entry_exit) Init(1) IntegerRange(0, 1) Param
+Emit instrumentation calls to __tsan_func_entry() and __tsan_func_exit().
+
 -param=uninit-control-dep-attempts=
 Common Joined UInteger Var(param_uninit_control_dep_attempts) Init(1000) IntegerRange(1, 65536) Param Optimization
 Maximum number of nested calls to search for control dependencies during uninitialized variable analysis.

gcc/testsuite/c-c++-common/tsan/func_entry_exit.c

@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-options "-fdump-tree-gimple -fdump-tree-optimized" } */
+
+int x;
+
+__attribute__((noinline))
+void fn1(void)
+{
+  x++;
+}
+
+__attribute__((noinline))
+void fn2(void)
+{
+  fn1();
+}
+
+__attribute__((noinline))
+int main(int argc, char *argv[])
+{
+  fn1();
+  fn2();
+  return 0;
+}
+
+// { dg-final { scan-tree-dump "TSAN_FUNC_EXIT" "gimple" } }
+// { dg-final { scan-tree-dump-times "__tsan_func_entry" 3 "optimized" } }
+// { dg-final { scan-tree-dump-times "__tsan_func_exit" 3 "optimized" } }
+// { dg-final { scan-tree-dump "__tsan_write" "optimized" } }

gcc/testsuite/c-c++-common/tsan/func_entry_exit_disabled.c

@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-options "--param=tsan-instrument-func-entry-exit=0 -fdump-tree-gimple -fdump-tree-optimized" } */
+
+int x;
+
+__attribute__((noinline))
+void fn1(void)
+{
+  x++;
+}
+
+__attribute__((noinline))
+void fn2(void)
+{
+  fn1();
+}
+
+__attribute__((noinline))
+int main(int argc, char *argv[])
+{
+  fn1();
+  fn2();
+  return 0;
+}
+
+// { dg-final { scan-tree-dump-not "TSAN_FUNC_EXIT" "gimple" } }
+// { dg-final { scan-tree-dump-not "__tsan_func_entry" "optimized" } }
+// { dg-final { scan-tree-dump-not "__tsan_func_exit" "optimized" } }
+// { dg-final { scan-tree-dump "__tsan_write" "optimized" } }

gcc/tsan.c

@@ -804,7 +804,9 @@ instrument_memory_accesses (bool *cfg_changed)
 	      func_exit_seen = true;
 	    }
 	  else
-	    fentry_exit_instrument |= instrument_gimple (&gsi);
+	    fentry_exit_instrument
+	      |= (instrument_gimple (&gsi)
+		  && param_tsan_instrument_func_entry_exit);
 	}
       if (gimple_purge_dead_eh_edges (bb))
 	*cfg_changed = true;