[libgomp, nvptx] Handle per-function max-threads-per-block in default dims

Currently parallel-loop-1.c fails at -O0 on a Quadro M1200, because one of the
kernel launch configurations exceeds the resources available in the device, due
to the default dimensions chosen by the runtime.

This patch fixes that by taking the per-function max_threads_per_block into
account when using the default dimensions.

2018-07-27  Tom de Vries  <tdevries@suse.de>

	* plugin/plugin-nvptx.c (MIN, MAX): Redefine.
	(nvptx_exec): Ensure worker and vector default dims don't exceed
	targ_fn->max_threads_per_block.

---
 libgomp/plugin/plugin-nvptx.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/libgomp/plugin/plugin-nvptx.c b/libgomp/plugin/plugin-nvptx.c
index 5c522aaf281..b6ec5f88d59 100644
--- a/libgomp/plugin/plugin-nvptx.c
+++ b/libgomp/plugin/plugin-nvptx.c
@@ -141,6 +141,11 @@ init_cuda_lib (void)
 
 #include "secure_getenv.h"
 
+#undef MIN
+#undef MAX
+#define MIN(X,Y) ((X) < (Y) ? (X) : (Y))
+#define MAX(X,Y) ((X) > (Y) ? (X) : (Y))
+
 /* Convenience macros for the frequently used CUDA library call and
    error handling sequence as well as CUDA library calls that
    do the error checking themselves or don't do it at all.  */
@@ -1135,6 +1140,7 @@ nvptx_exec (void (*fn), size_t mapnum, void **hostaddrs, void **devaddrs,
   void *kargs[1];
   void *hp, *dp;
   struct nvptx_thread *nvthd = nvptx_thread ();
+  int warp_size = nvthd->ptx_dev->warp_size;
   const char *maybe_abort_msg = "(perhaps abort was called)";
 
   function = targ_fn->fn;
@@ -1175,7 +1181,6 @@ nvptx_exec (void (*fn), size_t mapnum, void **hostaddrs, void **devaddrs,
 
 	  int gang, worker, vector;
 	  {
-	    int warp_size = nvthd->ptx_dev->warp_size;
 	    int block_size = nvthd->ptx_dev->max_threads_per_block;
 	    int cpu_size = nvthd->ptx_dev->max_threads_per_multiprocessor;
 	    int dev_size = nvthd->ptx_dev->num_sms;
@@ -1213,9 +1218,25 @@ nvptx_exec (void (*fn), size_t mapnum, void **hostaddrs, void **devaddrs,
 	}
       pthread_mutex_unlock (&ptx_dev_lock);
 
-      for (i = 0; i != GOMP_DIM_MAX; i++)
-	if (!dims[i])
-	  dims[i] = nvthd->ptx_dev->default_dims[i];
+      {
+	bool default_dim_p[GOMP_DIM_MAX];
+	for (i = 0; i != GOMP_DIM_MAX; i++)
+	  {
+	    default_dim_p[i] = !dims[i];
+	    if (default_dim_p[i])
+	      dims[i] = nvthd->ptx_dev->default_dims[i];
+	  }
+
+	if (default_dim_p[GOMP_DIM_VECTOR])
+	  dims[GOMP_DIM_VECTOR]
+	    = MIN (dims[GOMP_DIM_VECTOR],
+		   (targ_fn->max_threads_per_block / warp_size * warp_size));
+
+	if (default_dim_p[GOMP_DIM_WORKER])
+	  dims[GOMP_DIM_WORKER]
+	    = MIN (dims[GOMP_DIM_WORKER],
+		   targ_fn->max_threads_per_block / dims[GOMP_DIM_VECTOR]);
+      }
     }
 
   /* Check if the accelerator has sufficient hardware resources to