Default compute dimensions (compile time)

This patch was previously combined with an unrelated change and testcases
that was upstreamed separately ("Add '-Wopenacc-parallelism'",
22cff118f7526bec195ed6e41452980820fdf3a8).

gcc/ChangeLog
	* doc/invoke.texi (fopenacc-dim): Document syntax for using
	runtime value from environment variable.
	* omp-offload.cc (oacc_parse_default_dims): Implement it.

libgomp/ChangeLog
	* testsuite/libgomp.oacc-c-c++-common/loop-default-compile.c: New.

Co-Authored-By: Tom de Vries  <tdevries@suse.de>
Co-Authored-By: Thomas Schwinge  <thomas@codesourcery.com>
Co-Authored-By: Julian Brown  <julian@codesourcery.com>

2 files changed, 21 insertions, 10 deletions

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 617a3d8..f55f789 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -5249,7 +5249,11 @@ have support for @option{-pthread}.
 Specify default compute dimensions for parallel offload regions that do
 not explicitly specify them.  The @var{geom} value is a triple of
 @samp{:}-separated sizes, in order @var{gang}, @var{worker}, and @var{vector}.
-A size can be omitted, to use a target-specific default value.
+If a size is to be deferred until execution @samp{-} can be used;
+alternatively a size can be omitted to use a target-specific default value.
+When deferring to runtime, the environment variable @env{GOMP_OPENACC_DIM}
+can be set.  It has the same format as the option value, except that
+@samp{-} is not permitted.
 
 @opindex fopenmp
 @cindex OpenMP parallel
diff --git a/gcc/omp-offload.cc b/gcc/omp-offload.cc
index de9b063..536bfb7 100644
--- a/gcc/omp-offload.cc
+++ b/gcc/omp-offload.cc
@@ -875,8 +875,9 @@ oacc_get_min_dim (int dim)
 }
 
 /* Parse the default dimension parameter.  This is a set of
-   :-separated optional compute dimensions.  Each specified dimension
-   is a positive integer.  When device type support is added, it is
+   :-separated optional compute dimensions.  Each dimension is either
+   a positive integer, or '-' for a dynamic value computed at
+   runtime.  When device type support is added, it is
    planned to be a comma separated list of such compute dimensions,
    with all but the first prefixed by the colon-terminated device
    type.  */
@@ -911,14 +912,20 @@ oacc_parse_default_dims (const char *dims)
 
 	  if (*pos != ':')
 	    {
-	      long val;
-	      const char *eptr;
+	      long val = 0;
 
-	      errno = 0;
-	      val = strtol (pos, CONST_CAST (char **, &eptr), 10);
-	      if (errno || val <= 0 || (int) val != val)
-		goto malformed;
-	      pos = eptr;
+	      if (*pos == '-')
+		pos++;
+	      else
+		{
+		  const char *eptr;
+
+		  errno = 0;
+		  val = strtol (pos, CONST_CAST (char **, &eptr), 10);
+		  if (errno || val <= 0 || (int) val != val)
+		    goto malformed;
+		  pos = eptr;
+		}
 	      oacc_default_dims[ix] = (int) val;
 	    }
 	}