From: Jakub Jelinek <jakub@redhat.com>
Date: Thu, 2 Jul 2020 09:03:33 +0000 (+0200)
Subject: openmp: Diagnose non-rectangular loops with invalid steps
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=9d50112acfc01f85fe0fb6d88b329e6122e817b3;p=gcc.git

openmp: Diagnose non-rectangular loops with invalid steps

THe OpenMP 5 standard requires that if some loop in OpenMP loop nest refers
to some outer loop's iterator variable, then the subtraction of the multiplication
factors for the outer iterator multiplied by the outer increment modulo the
inner increment is 0.  For loops with non-constants in any of these we can't
diagnose it, it would be a task for something like -fsanitize=openmp,
but if all these are constant, we can diagnose it.

2020-07-02  Jakub Jelinek  <jakub@redhat.com>

	* omp-expand.c (expand_omp_for): Diagnose non-rectangular loops with
	invalid steps - ((m2 - m1) * incr_outer) % incr must be 0 in valid
	OpenMP non-rectangular loops.  Use XALLOCAVEC.

	* c-c++-common/gomp/loop-7.c: New test.
---

diff --git a/gcc/omp-expand.c b/gcc/omp-expand.c
index 0f07e51f7e8..b1349d8f088 100644
--- a/gcc/omp-expand.c
+++ b/gcc/omp-expand.c
@@ -7122,15 +7122,55 @@ expand_omp_for (struct omp_region *region, gimple *inner_stmt)
   struct omp_for_data fd;
   struct omp_for_data_loop *loops;
 
-  loops
-    = (struct omp_for_data_loop *)
-      alloca (gimple_omp_for_collapse (last_stmt (region->entry))
-	      * sizeof (struct omp_for_data_loop));
+  loops = XALLOCAVEC (struct omp_for_data_loop,
+		      gimple_omp_for_collapse (last_stmt (region->entry)));
   omp_extract_for_data (as_a <gomp_for *> (last_stmt (region->entry)),
 			&fd, loops);
   region->sched_kind = fd.sched_kind;
   region->sched_modifiers = fd.sched_modifiers;
   region->has_lastprivate_conditional = fd.lastprivate_conditional != 0;
+  if (fd.non_rect && !gimple_omp_for_combined_into_p (fd.for_stmt))
+    {
+      for (int i = fd.first_nonrect; i <= fd.last_nonrect; i++)
+	if ((loops[i].m1 || loops[i].m2)
+	    && (loops[i].m1 == NULL_TREE
+		|| TREE_CODE (loops[i].m1) == INTEGER_CST)
+	    && (loops[i].m2 == NULL_TREE
+		|| TREE_CODE (loops[i].m2) == INTEGER_CST)
+	    && TREE_CODE (loops[i].step) == INTEGER_CST
+	    && TREE_CODE (loops[i - loops[i].outer].step) == INTEGER_CST)
+	  {
+	    tree t;
+	    tree itype = TREE_TYPE (loops[i].v);
+	    if (loops[i].m1 && loops[i].m2)
+	      t = fold_build2 (MINUS_EXPR, itype, loops[i].m2, loops[i].m1);
+	    else if (loops[i].m1)
+	      t = fold_build1 (NEGATE_EXPR, itype, loops[i].m1);
+	    else
+	      t = loops[i].m2;
+	    t = fold_build2 (MULT_EXPR, itype, t,
+			     fold_convert (itype,
+					   loops[i - loops[i].outer].step));
+	    if (TYPE_UNSIGNED (itype) && loops[i].cond_code == GT_EXPR)
+	      t = fold_build2 (TRUNC_MOD_EXPR, itype,
+			       fold_build1 (NEGATE_EXPR, itype, t),
+			       fold_build1 (NEGATE_EXPR, itype,
+					    fold_convert (itype,
+							  loops[i].step)));
+	    else
+	      t = fold_build2 (TRUNC_MOD_EXPR, itype, t,
+			       fold_convert (itype, loops[i].step));
+	    if (integer_nonzerop (t))
+	      error_at (gimple_location (fd.for_stmt),
+			"invalid OpenMP non-rectangular loop step; "
+			"%<(%E - %E) * %E%> is not a multiple of loop %d "
+			"step %qE",
+			loops[i].m2 ? loops[i].m2 : integer_zero_node,
+			loops[i].m1 ? loops[i].m1 : integer_zero_node,
+			loops[i - loops[i].outer].step, i + 1,
+			loops[i].step);
+	  }
+    }
 
   gcc_assert (EDGE_COUNT (region->entry->succs) == 2);
   BRANCH_EDGE (region->entry)->flags &= ~EDGE_ABNORMAL;
diff --git a/gcc/testsuite/c-c++-common/gomp/loop-7.c b/gcc/testsuite/c-c++-common/gomp/loop-7.c
new file mode 100644
index 00000000000..4c8f27e76a5
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/gomp/loop-7.c
@@ -0,0 +1,24 @@
+void
+foo (void)
+{
+  #pragma omp for collapse(2)	/* { dg-error "invalid OpenMP non-rectangular loop step" } */
+  for (int i = 0; i < 6; i++)
+    for (int j = 4 * i; j < 7 * i; j += 2)
+      ;
+  #pragma omp for collapse(2)	/* { dg-error "invalid OpenMP non-rectangular loop step" } */
+  for (int i = 0; i < 32; i += 7)
+    for (int j = 3 * i; j < 7 * i; j += 30)
+      ;
+  #pragma omp for collapse(2)
+  for (int i = 0; i < 6; i++)
+    for (int j = 4 * i; j < 6 * i; j += 2)
+      ;
+  #pragma omp for collapse(2)
+  for (int i = 0; i < 6; i += 2)
+    for (int j = 4 * i; j < 7 * i; j += 2)
+      ;
+  #pragma omp for collapse(2)
+  for (int i = 0; i < 6; i += 5)
+    for (int j = 4 * i; j < 7 * i; j += 15)
+      ;
+}