In this failing testcase the LIM pass writes to g_13 regardless of the
initial value of g_13, which is the test protecting the write. This
causes an incorrect store data race wrt both the C++ memory model and
transactional memory (the latter if the store occurs inside of a
transaction).
The problem here is that the ``lsm_flag'' temporary should only be set
to true on the code paths where we actually set the original global. As
it stands, we are setting lsm_flag to true for reads or writes.
Fixed by only setting lsm_flag=1 when the original code path has a write.
Tested on x86-64 Linux.
OK for trunk?
PR middle-end/54149
* tree-ssa-loop-im.c (execute_sm_if_changed_flag_set): Only set
flag for writes.
diff --git a/gcc/testsuite/gcc.dg/simulate-thread/speculative-store-4.c
b/gcc/testsuite/gcc.dg/simulate-thread/speculative-store-4.c
new file mode 100644
index 0000000..735cf5b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/simulate-thread/speculative-store-4.c
@@ -0,0 +1,54 @@
+/* { dg-do link } */
+/* { dg-options "--param allow-store-data-races=0 -O" } */
+/* { dg-final { simulate-thread } } */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "simulate-thread.h"
+
+/* PR 54139 */
+/* Test that speculative stores do not happen for --param
+ allow-store-data-races=0. */
+
+int g_13=1, insns=1;
+
+__attribute__((noinline))
+void simulate_thread_main()
+{
+ int l_245;
+
+ /* Since g_13 is unilaterally set positive above, there should be
+ no store to g_13 below. */
+ for (l_245 = 0; l_245 <= 1; l_245 += 1)
+ for (; g_13 <= 0; g_13 = 1)
+ ;
+}
+
+int main()
+{
+ simulate_thread_main ();
+ simulate_thread_done ();
+ return 0;
+}
+
+void simulate_thread_other_threads ()
+{
+ ++g_13;
+ ++insns;
+}
+
+int simulate_thread_step_verify ()
+{
+ return 0;
+}
+
+int simulate_thread_final_verify ()
+{
+ if (g_13 != insns)
+ {
+ printf("FAIL: g_13 was incorrectly cached\n");
+ return 1;
+ }
+ return 0;
+}
diff --git a/gcc/tree-ssa-loop-im.c b/gcc/tree-ssa-loop-im.c
index 0f61631..c5fc324 100644
--- a/gcc/tree-ssa-loop-im.c
+++ b/gcc/tree-ssa-loop-im.c
@@ -2113,9 +2113,14 @@ execute_sm_if_changed_flag_set (struct loop *loop,
mem_ref_p ref)
gimple_stmt_iterator gsi;
gimple stmt;
- gsi = gsi_for_stmt (loc->stmt);
- stmt = gimple_build_assign (flag, boolean_true_node);
- gsi_insert_after (&gsi, stmt, GSI_CONTINUE_LINKING);
+ /* Only set the flag for writes. */
+ if (is_gimple_assign (loc->stmt)
+ && gimple_assign_lhs (loc->stmt) == *loc->ref)
+ {
+ gsi = gsi_for_stmt (loc->stmt);
+ stmt = gimple_build_assign (flag, boolean_true_node);
+ gsi_insert_after (&gsi, stmt, GSI_CONTINUE_LINKING);
+ }
}
VEC_free (mem_ref_loc_p, heap, locs);
return flag;
