openmp: Fix ICE on non-rectangular loop with known 0 iterations [PR97862]

openmp: Fix ICE on non-rectangular loop with known 0 iterations [PR97862]

[Jakub Jelinek]

Hi!

The loops in the testcase are non-rectangular and have 0 iterations
(the outer loop iterates, but the inner one never).  In this case we
just have the overall number of iterations computed (0), and don't have
factor and other values computed.  We never need to map logical iterations
to the individual iterations in that case, and we were crashing during
expansion of that code.

Bootstrapped/regtested on x86_64-linux and i686-linux, committed to trunk.

2020-11-18  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/97862
	* omp-expand.c (expand_omp_for_init_vars): Don't use the sqrt path
	if number of iterations is constant 0.

	* c-c++-common/gomp/pr97862.c: New test.

--- gcc/omp-expand.c.jj	2020-11-14 10:40:11.231409596 +0100
+++ gcc/omp-expand.c	2020-11-17 12:56:52.183888420 +0100
@@ -2514,7 +2514,8 @@ expand_omp_for_init_vars (struct omp_for
 	      && (TREE_CODE (fd->loop.n2) == INTEGER_CST
 		  || fd->first_inner_iterations)
 	      && (optab_handler (sqrt_optab, TYPE_MODE (double_type_node))
-		  != CODE_FOR_nothing))
+		  != CODE_FOR_nothing)
+	      && !integer_zerop (fd->loop.n2))
 	    {
 	      tree outer_n1 = fd->adjn1 ? fd->adjn1 : fd->loops[i - 1].n1;
 	      tree itype = TREE_TYPE (fd->loops[i].v);
--- gcc/testsuite/c-c++-common/gomp/pr97862.c.jj	2020-11-17 13:00:31.019380920 +0100
+++ gcc/testsuite/c-c++-common/gomp/pr97862.c	2020-11-17 13:04:05.602922138 +0100
@@ -0,0 +1,15 @@
+/* PR middle-end/97862 */
+
+void
+foo (void)
+{
+  int i, j;
+#pragma omp for collapse(2)
+  for (i = 0; i < 1; ++i)
+    for (j = 0; j < i; ++j)
+      ;
+#pragma omp for collapse(2)
+  for (i = 0; i < 20; i++)
+    for (j = 0; j < i - 19; j += 1)
+      ;
+}

	Jakub