Enhance if-conversion for automatic arrays

Automatic arrays that are not address-taken should not be subject to
store data races.  This applies to OMP SIMD in-branch lowered
functions result array which for the testcase otherwise prevents
vectorization with SSE and for AVX and AVX512 ends up with spurious
.MASK_STORE to the stack surviving.

This inefficiency was noted in PR111793.

I've introduced ref_can_have_store_data_races, commonizing uses
of flag_store_data_races in if-conversion, cselim and store motion.

	PR tree-optimization/111793
	* tree-ssa-alias.h (ref_can_have_store_data_races): Declare.
	* tree-ssa-alias.cc (ref_can_have_store_data_races): New
	function.
	* tree-if-conv.cc (ifcvt_memrefs_wont_trap): Use
	ref_can_have_store_data_races to allow more unconditional
	stores.
	* tree-ssa-loop-im.cc (execute_sm): Likewise.
	* tree-ssa-phiopt.cc (cond_store_replacement): Likewise.

	* gcc.dg/vect/vect-simd-clone-21.c: New testcase.

6 files changed, 44 insertions, 10 deletions

diff --git a/gcc/testsuite/gcc.dg/vect/vect-simd-clone-21.c b/gcc/testsuite/gcc.dg/vect/vect-simd-clone-21.c
new file mode 100644
index 0000000..49c52fb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-simd-clone-21.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target vect_simd_clones } */
+/* { dg-additional-options "-fopenmp-simd" } */
+
+#pragma omp declare simd simdlen(4) inbranch
+__attribute__((noinline)) int
+foo (int a, int b)
+{
+  return a + b;
+}
+
+/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 4 "vect" { target i?86-*-* x86_64-*-* } } } */
+/* if-conversion shouldn't need to resort to masked stores for the result
+   array created by OMP lowering since that's automatic and does not have
+   its address taken.  */
+/* { dg-final { scan-tree-dump-not "MASK_STORE" "vect" } } */
diff --git a/gcc/tree-if-conv.cc b/gcc/tree-if-conv.cc
index c4c3ed4..57992b6 100644
--- a/gcc/tree-if-conv.cc
+++ b/gcc/tree-if-conv.cc
@@ -936,12 +936,11 @@ ifcvt_memrefs_wont_trap (gimple *stmt, vec<data_reference_p> drs)
 
       /* an unconditionaly write won't trap if the base is written
          to unconditionally.  */
-      if (base_master_dr
-	  && DR_BASE_W_UNCONDITIONALLY (*base_master_dr))
-	return flag_store_data_races;
-      /* or the base is known to be not readonly.  */
-      else if (base_object_writable (DR_REF (a)))
-	return flag_store_data_races;
+      if ((base_master_dr
+	   && DR_BASE_W_UNCONDITIONALLY (*base_master_dr))
+	  /* or the base is known to be not readonly.  */
+	  || base_object_writable (DR_REF (a)))
+	return !ref_can_have_store_data_races (base);
     }
 
   return false;
diff --git a/gcc/tree-ssa-alias.cc b/gcc/tree-ssa-alias.cc
index 1a91d63..fab048b 100644
--- a/gcc/tree-ssa-alias.cc
+++ b/gcc/tree-ssa-alias.cc
@@ -3704,6 +3704,25 @@ stmt_kills_ref_p (gimple *stmt, tree ref)
   return stmt_kills_ref_p (stmt, &r);
 }
 
+/* Return whether REF can be subject to store data races.  */
+
+bool
+ref_can_have_store_data_races (tree ref)
+{
+  /* With -fallow-store-data-races do not care about them.  */
+  if (flag_store_data_races)
+    return false;
+
+  tree base = get_base_address (ref);
+  if (auto_var_p (base)
+      && ! may_be_aliased (base))
+    /* Automatic variables not aliased are not subject to
+       data races.  */
+    return false;
+
+  return true;
+}
+
 
 /* Walk the virtual use-def chain of VUSE until hitting the virtual operand
    TARGET or a statement clobbering the memory reference REF in which
diff --git a/gcc/tree-ssa-alias.h b/gcc/tree-ssa-alias.h
index 5cd64e7..5834533 100644
--- a/gcc/tree-ssa-alias.h
+++ b/gcc/tree-ssa-alias.h
@@ -144,6 +144,8 @@ extern bool call_may_clobber_ref_p (gcall *, tree, bool = true);
 extern bool call_may_clobber_ref_p_1 (gcall *, ao_ref *, bool = true);
 extern bool stmt_kills_ref_p (gimple *, tree);
 extern bool stmt_kills_ref_p (gimple *, ao_ref *);
+extern bool ref_can_have_store_data_races (tree);
+
 enum translate_flags
   { TR_TRANSLATE, TR_VALUEIZE_AND_DISAMBIGUATE, TR_DISAMBIGUATE };
 extern tree get_continuation_for_phi (gimple *, ao_ref *, bool,
diff --git a/gcc/tree-ssa-loop-im.cc b/gcc/tree-ssa-loop-im.cc
index f3fda2b..3acbd88 100644
--- a/gcc/tree-ssa-loop-im.cc
+++ b/gcc/tree-ssa-loop-im.cc
@@ -2298,7 +2298,7 @@ execute_sm (class loop *loop, im_mem_ref *ref,
   bool always_stored = ref_always_accessed_p (loop, ref, true);
   if (maybe_mt
       && (bb_in_transaction (loop_preheader_edge (loop)->src)
-	  || (! flag_store_data_races && ! always_stored)))
+	  || (ref_can_have_store_data_races (ref->mem.ref) && ! always_stored)))
     multi_threaded_model_p = true;
 
   if (multi_threaded_model_p && !use_other_flag_var)
diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index 0ef42a1..f05ca72 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -3343,9 +3343,7 @@ cond_store_replacement (basic_block middle_bb, basic_block join_bb,
       /* If LHS is an access to a local variable without address-taken
 	 (or when we allow data races) and known not to trap, we could
 	 always safely move down the store.  */
-      tree base = get_base_address (lhs);
-      if (!auto_var_p (base)
-	  || (TREE_ADDRESSABLE (base) && !flag_store_data_races)
+      if (ref_can_have_store_data_races (lhs)
 	  || tree_could_trap_p (lhs))
 	return false;
     }