[gcc/devel/omp/gcc-11] openacc: Handle internal function calls in pass_lim

[gcc/devel/omp/gcc-11] openacc: Handle internal function calls in pass_lim

[Frederik Harwath]

https://gcc.gnu.org/g:2da00a40daf6dd5aac10f0c5616a6cee7f960e5f

commit 2da00a40daf6dd5aac10f0c5616a6cee7f960e5f
Author: Frederik Harwath <frederik@codesourcery.com>
Date:   Tue Nov 16 16:20:41 2021 +0100

    openacc: Handle internal function calls in pass_lim
    
    The loop invariant motion pass correctly refuses to move statements
    out of a loop if any other statement in the loop is unanalyzable.  The
    pass does not know how to handle the OpenACC internal function calls
    which was not necessary until recently when the OpenACC device
    lowering pass was moved to a later position in the pass pipeline.
    
    This commit changes pass_lim to ignore the OpenACC internal function
    calls which do not contain any memory references. The hoisting enabled
    by this change can be useful for the data-dependence analysis in
    Graphite; for instance, in the outlined functions for OpenACC regions,
    all invariant accesses to the ".omp_data_i" struct should be hoisted
    out of the OpenACC loop.  This is particularly important for variables
    that were scalars in the original loop and which have been turned into
    accesses to the struct by the outlining process.  Not hoisting those
    can prevent scalar evolution analysis which is crucial for Graphite.
    Since any hoisting that introduces intermediate names - and hence,
    "fake" dependences - inside the analyzed nest can be harmful to
    data-dependence analysis, a flag to restrict the hoisting in OpenACC
    functions is added to the pass. The pass instance that executes before
    Graphite now runs with this flag set to true and the pass instance
    after Graphite runs unrestricted.
    
    A more precise way of selecting the statements for which hoisting
    should be enabled is left for a future improvement.
    
    gcc/ChangeLog:
            * passes.def: Set restrict_oacc_hoisting to true for the early
            pass_lim instance.
            * tree-ssa-loop-im.c (movement_possibility): Add
            restrict_oacc_hoisting flag to function; restrict movement if set.
            (compute_invariantness): Add restrict_oacc_hoisting flag and pass it on.
            (gather_mem_refs_stmt): Skip IFN_GOACC_LOOP and IFN_UNIQUE
            calls.
            (loop_invariant_motion_in_fun): Add restrict_oacc_hoisting flag and
            pass it on.
            (pass_lim::execute): Pass on new flags.
            * tree-ssa-loop-manip.h (loop_invariant_motion_in_fun): Adjust declaration.
            * gimple-loop-interchange.cc (pass_linterchange::execute): Adjust call to
            loop_invariant_motion_in_fun.

Diff:
---
 gcc/gimple-loop-interchange.cc |  2 +-
 gcc/passes.def                 |  2 +-
 gcc/tree-ssa-loop-im.c         | 58 +++++++++++++++++++++++++++++++++++-------
 gcc/tree-ssa-loop-manip.h      |  2 +-
 4 files changed, 52 insertions(+), 12 deletions(-)

diff --git a/gcc/gimple-loop-interchange.cc b/gcc/gimple-loop-interchange.cc
index 7b799eca805..d617438910f 100644
--- a/gcc/gimple-loop-interchange.cc
+++ b/gcc/gimple-loop-interchange.cc
@@ -2096,7 +2096,7 @@ pass_linterchange::execute (function *fun)
   if (changed_p)
     {
       unsigned todo = TODO_update_ssa_only_virtuals;
-      todo |= loop_invariant_motion_in_fun (cfun, false);
+      todo |= loop_invariant_motion_in_fun (cfun, false, false);
       scev_reset ();
       return todo;
     }
diff --git a/gcc/passes.def b/gcc/passes.def
index 48c9821011f..d1dedbc287e 100644
--- a/gcc/passes.def
+++ b/gcc/passes.def
@@ -247,7 +247,7 @@ along with GCC; see the file COPYING3.  If not see
       NEXT_PASS (pass_cse_sincos);
       NEXT_PASS (pass_optimize_bswap);
       NEXT_PASS (pass_laddress);
-      NEXT_PASS (pass_lim);
+      NEXT_PASS (pass_lim, true /* restrict_oacc_hoisting */);
       NEXT_PASS (pass_walloca, false);
       NEXT_PASS (pass_pre);
       NEXT_PASS (pass_sink_code);
diff --git a/gcc/tree-ssa-loop-im.c b/gcc/tree-ssa-loop-im.c
index 7de47edbcb3..b392ae609aa 100644
--- a/gcc/tree-ssa-loop-im.c
+++ b/gcc/tree-ssa-loop-im.c
@@ -47,6 +47,8 @@ along with GCC; see the file COPYING3.  If not see
 #include "builtins.h"
 #include "tree-dfa.h"
 #include "dbgcnt.h"
+#include "graphite-oacc.h"
+#include "internal-fn.h"
 
 /* TODO:  Support for predicated code motion.  I.e.
 
@@ -320,11 +322,23 @@ enum move_pos
    Otherwise return MOVE_IMPOSSIBLE.  */
 
 enum move_pos
-movement_possibility (gimple *stmt)
+movement_possibility (gimple *stmt, bool restrict_oacc_hoisting)
 {
   tree lhs;
   enum move_pos ret = MOVE_POSSIBLE;
 
+  if (restrict_oacc_hoisting && oacc_get_fn_attrib (cfun->decl)
+      && gimple_code (stmt) == GIMPLE_ASSIGN)
+    {
+      tree rhs = gimple_assign_rhs1 (stmt);
+
+      if (TREE_CODE (rhs) == VIEW_CONVERT_EXPR)
+	rhs = TREE_OPERAND (rhs, 0);
+
+      if (TREE_CODE (rhs) == ARRAY_REF)
+	  return MOVE_IMPOSSIBLE;
+    }
+
   if (flag_unswitch_loops
       && gimple_code (stmt) == GIMPLE_COND)
     {
@@ -974,7 +988,7 @@ rewrite_bittest (gimple_stmt_iterator *bsi)
    statements.  */
 
 static void
-compute_invariantness (basic_block bb)
+compute_invariantness (basic_block bb, bool restrict_oacc_hoisting)
 {
   enum move_pos pos;
   gimple_stmt_iterator bsi;
@@ -1002,7 +1016,7 @@ compute_invariantness (basic_block bb)
       {
 	stmt = gsi_stmt (bsi);
 
-	pos = movement_possibility (stmt);
+	pos = movement_possibility (stmt, restrict_oacc_hoisting);
 	if (pos == MOVE_IMPOSSIBLE)
 	  continue;
 
@@ -1033,7 +1047,7 @@ compute_invariantness (basic_block bb)
     {
       stmt = gsi_stmt (bsi);
 
-      pos = movement_possibility (stmt);
+      pos = movement_possibility (stmt, restrict_oacc_hoisting);
       if (pos == MOVE_IMPOSSIBLE)
 	{
 	  if (nonpure_call_p (stmt))
@@ -1458,7 +1472,15 @@ gather_mem_refs_stmt (class loop *loop, gimple *stmt)
   if (!gimple_vuse (stmt))
     return;
 
+  /* The expansion of those OpenACC internal function calls which occurs in a
+   * later pass does not introduce any memory references. Hence it is safe to
+   * ignore them. */
+  if (gimple_call_internal_p (stmt, IFN_GOACC_LOOP)
+      || gimple_call_internal_p (stmt, IFN_UNIQUE))
+    return;
+
   mem = simple_mem_ref_in_stmt (stmt, &is_stored);
+
   if (!mem)
     {
       /* We use the shared mem_ref for all unanalyzable refs.  */
@@ -1484,7 +1506,7 @@ gather_mem_refs_stmt (class loop *loop, gimple *stmt)
       ao_ref_alias_set (&aor);
       HOST_WIDE_INT offset, size, max_size;
       poly_int64 saved_maxsize = aor.max_size, mem_off;
-      tree mem_base;
+      tree mem_base = NULL;
       bool ref_decomposed;
       if (aor.max_size_known_p ()
 	  && aor.offset.is_constant (&offset)
@@ -3155,7 +3177,8 @@ tree_ssa_lim_finalize (void)
    Only perform store motion if STORE_MOTION is true.  */
 
 unsigned int
-loop_invariant_motion_in_fun (function *fun, bool store_motion)
+loop_invariant_motion_in_fun (function *fun, bool store_motion,
+			      bool restrict_oacc_hoisting)
 {
   unsigned int todo = 0;
 
@@ -3173,7 +3196,7 @@ loop_invariant_motion_in_fun (function *fun, bool store_motion)
   /* For each statement determine the outermost loop in that it is
      invariant and cost for computing the invariant.  */
   for (int i = 0; i < n; ++i)
-    compute_invariantness (BASIC_BLOCK_FOR_FN (fun, rpo[i]));
+    compute_invariantness (BASIC_BLOCK_FOR_FN (fun, rpo[i]), restrict_oacc_hoisting);
 
   /* Execute store motion.  Force the necessary invariants to be moved
      out of the loops as well.  */
@@ -3220,13 +3243,21 @@ class pass_lim : public gimple_opt_pass
 {
 public:
   pass_lim (gcc::context *ctxt)
-    : gimple_opt_pass (pass_data_lim, ctxt)
+    : gimple_opt_pass (pass_data_lim, ctxt), restrict_oacc_hoisting (false)
   {}
 
+  void set_pass_param (unsigned int n, bool param)
+    {
+      gcc_assert (n == 0);
+      restrict_oacc_hoisting = param;
+    }
+
   /* opt_pass methods: */
   opt_pass * clone () { return new pass_lim (m_ctxt); }
   virtual bool gate (function *) { return flag_tree_loop_im != 0; }
   virtual unsigned int execute (function *);
+private:
+  bool restrict_oacc_hoisting;
 
 }; // class pass_lim
 
@@ -3239,7 +3270,16 @@ pass_lim::execute (function *fun)
 
   if (number_of_loops (fun) <= 1)
     return 0;
-  unsigned int todo = loop_invariant_motion_in_fun (fun, true);
+
+  bool store_motion = true;
+  /* TODO Enabling store motion in OpenACC kernel functions requires further
+     handling of the OpenACC internal function calls.  It can also be harmful
+     to data-dependence analysis. Keep it disabled for now. */
+  if (oacc_function_p (cfun) && graphite_analyze_oacc_target_region_type_p (cfun))
+    store_motion = false;
+
+  unsigned int todo = loop_invariant_motion_in_fun (fun, store_motion,
+						    restrict_oacc_hoisting);
 
   if (!in_loop_pipeline)
     loop_optimizer_finalize ();
diff --git a/gcc/tree-ssa-loop-manip.h b/gcc/tree-ssa-loop-manip.h
index 86fc118b6be..e0beb624aec 100644
--- a/gcc/tree-ssa-loop-manip.h
+++ b/gcc/tree-ssa-loop-manip.h
@@ -55,7 +55,7 @@ extern void tree_transform_and_unroll_loop (class loop *, unsigned,
 extern void tree_unroll_loop (class loop *, unsigned,
 			      edge, class tree_niter_desc *);
 extern tree canonicalize_loop_ivs (class loop *, tree *, bool);
-extern unsigned int loop_invariant_motion_in_fun (function *, bool);
+extern unsigned int loop_invariant_motion_in_fun (function *, bool, bool);
 
 
 #endif /* GCC_TREE_SSA_LOOP_MANIP_H */