Here is the updated patch, which follow UD chain to determine whether
iv.base is defined by __gcovx.xxx[] var. It is a lot simpler than
adding a tree bit.
regression test and previously failed benchmark in piii mode is ok.
Other test is going on.
2014-02-10 Wei Mi <w...@google.com>
* tree-ssa-loop-ivopts.c (defined_by_gcov_counter): New.
(contains_abnormal_ssa_name_p): Add defined_by_gcov_counter
check for ssa name.
* testsuite/gcc.dg/profile-generate-4.c: New.
Index: tree-ssa-loop-ivopts.c
===================================================================
--- tree-ssa-loop-ivopts.c (revision 207019)
+++ tree-ssa-loop-ivopts.c (working copy)
@@ -705,6 +705,68 @@ idx_contains_abnormal_ssa_name_p (tree b
return !abnormal_ssa_name_p (*index);
}
+/* Return true if the use is defined by a gcov counter var.
+ It is used to check if an iv candidate is generated for
+ profiling. For profile generated ssa name, we should not
+ use it as IV because gcov counter may have data-race for
+ multithread program, it could involve tricky bug to use
+ such ssa var in IVOPT.
+
+ To limit patterns to be checked, we list the possible cases
+ here:
+ Before PRE, the ssa name used to set __gcov counter is as
+ follows:
+ for () {
+ PROF_edge_counter_1 = __gcov.foo[i];
+ PROF_edge_counter_2 = PROF_edge_counter_1 + 1;
+ __gcov.foo[i] = PROF_edge_counter_2;
+ }
+ If PRE works, the loop may be transformed to:
+ pretmp_1 = __gcov.foo[i];
+ for () {
+ prephitmp_1 = PHI (PROF_edge_counter_2, pretmp_1);
+ PROF_edge_counter_1 = prephitmp_1;
+ PROF_edge_counter_2 = PROF_edge_counter_1 + 1;
+ __gcov.foo[i] = PROF_edge_counter_2;
+ }
+ So there are two cases:
+ case1: If PRE doesn't work, PROF_edge_counter_1 and PROF_edge_counter_2
+ are neither induction variables candidates. We don't have to worry
+ about this case.
+ case2: If PRE works, the iv candidate base of PROF_edge_counter_1 and
+ PROF_edge_counter_2 are pretmp_1 or pretmp_1 + 1. pretmp_1 is defined
+ by __gcov var.
+
+ So this func only has to check case2. For a ssa name which is an iv
+ candidate, check its base USE and see if it is defined by __gcov var.
+ Returning true means the ssa name is generated for profiling. */
+
+bool
+defined_by_gcov_counter (tree use)
+{
+ gimple stmt;
+ tree rhs, decl;
+ const char *name;
+
+ stmt = SSA_NAME_DEF_STMT (use);
+ if (!is_gimple_assign (stmt))
+ return false;
+
+ rhs = gimple_assign_rhs1 (stmt);
+ if (TREE_CODE (rhs) != ARRAY_REF)
+ return false;
+
+ decl = TREE_OPERAND (rhs, 0);
+ if (TREE_CODE (decl) != VAR_DECL)
+ return false;
+
+ name = IDENTIFIER_POINTER (DECL_NAME (decl));
+ if (strncmp (name, "__gcov", 6))
+ return false;
+
+ return true;
+}
+
/* Returns true if EXPR contains a ssa name that occurs in an
abnormal phi node. */
@@ -721,7 +783,8 @@ contains_abnormal_ssa_name_p (tree expr)
codeclass = TREE_CODE_CLASS (code);
if (code == SSA_NAME)
- return SSA_NAME_OCCURS_IN_ABNORMAL_PHI (expr) != 0;
+ return SSA_NAME_OCCURS_IN_ABNORMAL_PHI (expr) != 0
+ || defined_by_gcov_counter (expr);
if (code == INTEGER_CST
|| is_gimple_min_invariant (expr))
Index: testsuite/gcc.dg/profile-generate-4.c
===================================================================
--- testsuite/gcc.dg/profile-generate-4.c (revision 0)
+++ testsuite/gcc.dg/profile-generate-4.c (revision 0)
@@ -0,0 +1,21 @@
+/* { dg-do compile { target { i?86-*-* x86_64-*-* } } } */
+/* { dg-options "-O2 -fprofile-generate -fno-tree-loop-im
-fdump-tree-ivopts-details-blocks" } */
+
+/* Because gcov counter related var has data race for multithread program,
+ compiler should prevent them from affecting program correctness. So
+ PROF_edge_counter variable should not be used as induction variable, or
+ else IVOPT may use such variable to compute loop boundary. */
+
+void *ptr;
+int N;
+
+void foo(void *t) {
+ int i;
+ for (i = 0; i < N; i++) {
+ t = *(void **)t;
+ }
+ ptr = t;
+}
+
+/* { dg-final { scan-tree-dump-times "ssa name PROF_edge_counter" 0
"ivopts"} } */
+/* { dg-final { cleanup-tree-dump "ivopts" } } */
