[ptx] partitioning optimization

[Nathan Sidwell <nathan at acm dot org>]

I've committed this patch to trunk.  It implements a partitioning optimization 
for a loop partitioned over both vector and worker axes.  We can elide the inner 
vector partitioning state propagation, if there are no intervening instructions 
in the worker-partitioned outer loop other than the forking and joining.  We 
simply execute the worker propagation on all vectors.

I've been unable to introduce a testcase for this. The difficulty is we want to 
check an rtl dump from the acceleration compiler, and there doesn't  appear to 
be existing machinery for that in the testsuite.  Perhaps something to be added 
later?

nathan

2015-11-10  Nathan Sidwell  <nathan@codesourcery.com>

	* config/nvptx/nvptx.opt (moptimize): New flag.
	* config/nvptx/nvptx.c (nvptx_option_override): Set nvptx_optimize
	default.
	(nvptx_optimize_inner): New.
	(nvptx_process_pars): Call it when optimizing.
	* doc/invoke.texi (Nvidia PTX Options): Document -moptimize.

Index: config/nvptx/nvptx.c
===================================================================
--- config/nvptx/nvptx.c	(revision 230112)
+++ config/nvptx/nvptx.c	(working copy)
@@ -137,6 +137,9 @@ nvptx_option_override (void)
   write_symbols = NO_DEBUG;
   debug_info_level = DINFO_LEVEL_NONE;
 
+  if (nvptx_optimize < 0)
+    nvptx_optimize = optimize > 0;
+
   declared_fndecls_htab = hash_table<tree_hasher>::create_ggc (17);
   needed_fndecls_htab = hash_table<tree_hasher>::create_ggc (17);
   declared_libfuncs_htab
@@ -2942,6 +2945,69 @@ nvptx_skip_par (unsigned mask, parallel
   nvptx_single (mask, par->forked_block, pre_tail);
 }
 
+/* If PAR has a single inner parallel and PAR itself only contains
+   empty entry and exit blocks, swallow the inner PAR.  */
+
+static void
+nvptx_optimize_inner (parallel *par)
+{
+  parallel *inner = par->inner;
+
+  /* We mustn't be the outer dummy par.  */
+  if (!par->mask)
+    return;
+
+  /* We must have a single inner par.  */
+  if (!inner || inner->next)
+    return;
+
+  /* We must only contain 2 blocks ourselves -- the head and tail of
+     the inner par.  */
+  if (par->blocks.length () != 2)
+    return;
+
+  /* We must be disjoint partitioning.  As we only have vector and
+     worker partitioning, this is sufficient to guarantee the pars
+     have adjacent partitioning.  */
+  if ((par->mask & inner->mask) & (GOMP_DIM_MASK (GOMP_DIM_MAX) - 1))
+    /* This indicates malformed code generation.  */
+    return;
+
+  /* The outer forked insn should be immediately followed by the inner
+     fork insn.  */
+  rtx_insn *forked = par->forked_insn;
+  rtx_insn *fork = BB_END (par->forked_block);
+
+  if (NEXT_INSN (forked) != fork)
+    return;
+  gcc_checking_assert (recog_memoized (fork) == CODE_FOR_nvptx_fork);
+
+  /* The outer joining insn must immediately follow the inner join
+     insn.  */
+  rtx_insn *joining = par->joining_insn;
+  rtx_insn *join = inner->join_insn;
+  if (NEXT_INSN (join) != joining)
+    return;
+
+  /* Preconditions met.  Swallow the inner par.  */
+  if (dump_file)
+    fprintf (dump_file, "Merging loop %x [%d,%d] into %x [%d,%d]\n",
+	     inner->mask, inner->forked_block->index,
+	     inner->join_block->index,
+	     par->mask, par->forked_block->index, par->join_block->index);
+
+  par->mask |= inner->mask & (GOMP_DIM_MASK (GOMP_DIM_MAX) - 1);
+
+  par->blocks.reserve (inner->blocks.length ());
+  while (inner->blocks.length ())
+    par->blocks.quick_push (inner->blocks.pop ());
+
+  par->inner = inner->inner;
+  inner->inner = NULL;
+
+  delete inner;
+}
+
 /* Process the parallel PAR and all its contained
    parallels.  We do everything but the neutering.  Return mask of
    partitioned modes used within this parallel.  */
@@ -2949,6 +3015,9 @@ nvptx_skip_par (unsigned mask, parallel
 static unsigned
 nvptx_process_pars (parallel *par)
 {
+  if (nvptx_optimize)
+    nvptx_optimize_inner (par);
+  
   unsigned inner_mask = par->mask;
 
   /* Do the inner parallels first.  */
Index: config/nvptx/nvptx.opt
===================================================================
--- config/nvptx/nvptx.opt	(revision 230112)
+++ config/nvptx/nvptx.opt	(working copy)
@@ -28,3 +28,7 @@ Generate code for a 64-bit ABI.
 mmainkernel
 Target Report RejectNegative
 Link in code for a __main kernel.
+
+moptimize
+Target Report Var(nvptx_optimize) Init(-1)
+Optimize partition neutering
Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi	(revision 230112)
+++ doc/invoke.texi	(working copy)
@@ -873,7 +873,7 @@ Objective-C and Objective-C++ Dialects}.
 -march=@var{arch} -mbmx -mno-bmx -mcdx -mno-cdx}
 
 @emph{Nvidia PTX Options}
-@gccoptlist{-m32 -m64 -mmainkernel}
+@gccoptlist{-m32 -m64 -mmainkernel -moptimize}
 
 @emph{PDP-11 Options}
 @gccoptlist{-mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45  -m10 @gol
@@ -18960,6 +18960,11 @@ Generate code for 32-bit or 64-bit ABI.
 Link in code for a __main kernel.  This is for stand-alone instead of
 offloading execution.
 
+@item -moptimize
+@opindex moptimize
+Apply partitioned execution optimizations.  This is the default when any
+level of optimization is selected.
+
 @end table
 
 @node PDP-11 Options