[PATCH, SMS] Fix violation of memory dependence

Revital Eres revital.eres@linaro.org
Mon Jun 13 09:13:00 GMT 2011


Hello,

The attached patch fixes violation of memory dependencies. The
problematic scenario happens when -fmodulo-sched-allow-regmoves flag
is set and certain anti-dep edges are not created.

For example, consider the following three instructions and the edges
between them.  When -fmodulo-sched-allow-regmoves is set the edge (63 -
Anti, 0 -> 64) is not created. (probably due to transitivity)

Insn 63)  r168 = MEM[176]
Out edges: (63 - Anti, 0 -> 64)
In edges: (64 - True, 1 -> 63), (68 - True, 1 -> 63)

insn 64)  176 = 176 + 4
Out edges: (64 - True, 1 -> 63), (64 - True, 0-> 68)
In edges: (63 - Anti, 0 -> 64)

insn 68)  MEM[176 – 4] =  193
Out edges: (68 - True, 1 -> 63)
In edges: (64 - True, 0-> 68)

This anti-dep edge is on the path from one memory instruction to another
--- from 63 to 68; such that removing the edge caused a violation of
the memory dependencies as insn 63 was scheduled after insn 68.

This patch adds intra edges between every two memory instructions in
this case.  It fixes recent bootstrap failure on ARM. (with SMS flags)

The patch was tested as follows:
On ppc64-redhat-linux regtest as well as bootstrap with SMS flags
enabling SMS also on loops with stage count 1.  Regtested on SPU.
On arm-linux-gnueabi bootstrap c language with SMS
flags enabling SMS also on loops with stage count 1
and currently regression testing on c,c++.

OK for mainline once regtest on arm-linux-gnueabi completes?

Thanks,
Revital

Changelog:

gcc/
        * ddg.c (add_intra_loop_mem_dep): New function.
        (build_intra_loop_deps): Call it.

testsuite/
        * gcc.dg/sms-9.c: New file.
-------------- next part --------------
Index: ddg.c
===================================================================
--- ddg.c	(revision 174906)
+++ ddg.c	(working copy)
@@ -390,6 +390,36 @@ insns_may_alias_p (rtx insn1, rtx insn2)
 			 &PATTERN (insn2));
 }
 
+/* Given two nodes, analyze their RTL insns and add intra-loop mem deps
+   to ddg G.  */
+static void
+add_intra_loop_mem_dep (ddg_ptr g, ddg_node_ptr from, ddg_node_ptr to)
+{
+
+  if (!insns_may_alias_p (from->insn, to->insn))
+    /* Do not create edge if memory references have disjoint alias sets.  */
+    return;
+
+  if (mem_write_insn_p (from->insn))
+    {
+      if (mem_read_insn_p (to->insn))
+	create_ddg_dep_no_link (g, from, to,
+				DEBUG_INSN_P (to->insn)
+				? ANTI_DEP : TRUE_DEP, MEM_DEP, 0);
+      else if (from->cuid != to->cuid)
+	create_ddg_dep_no_link (g, from, to,
+				DEBUG_INSN_P (to->insn)
+				? ANTI_DEP : OUTPUT_DEP, MEM_DEP, 0);
+    }
+  else
+    {
+      if (mem_read_insn_p (to->insn))
+	return;
+      else if (from->cuid != to->cuid)
+	create_ddg_dep_no_link (g, from, to, ANTI_DEP, MEM_DEP, 0);
+    }
+}
+
 /* Given two nodes, analyze their RTL insns and add inter-loop mem deps
    to ddg G.  */
 static void
@@ -477,10 +507,22 @@ build_intra_loop_deps (ddg_ptr g)
 	      if (DEBUG_INSN_P (j_node->insn))
 		continue;
 	      if (mem_access_insn_p (j_node->insn))
- 		/* Don't bother calculating inter-loop dep if an intra-loop dep
-		   already exists.  */
+		{
+		  /* Don't bother calculating inter-loop dep if an intra-loop dep
+		     already exists.  */
 	      	  if (! TEST_BIT (dest_node->successors, j))
 		    add_inter_loop_mem_dep (g, dest_node, j_node);
+		  /* If -fmodulo-sched-allow-regmoves
+		     is set certain anti-dep edges are not created.
+		     It might be that these anti-dep edges are on the
+		     path from one memory instruction to another such that
+		     removing these edges could cause a violation of the
+		     memory dependencies.  Thus we add intra edges between
+		     every two memory instructions in this case.  */
+		  if (flag_modulo_sched_allow_regmoves
+		      && !TEST_BIT (dest_node->predecessors, j))
+		    add_intra_loop_mem_dep (g, j_node, dest_node);
+		}
             }
         }
     }
Index: testsuite/gcc.dg/sms-9.c
===================================================================
--- testsuite/gcc.dg/sms-9.c	(revision 0)
+++ testsuite/gcc.dg/sms-9.c	(revision 0)
@@ -0,0 +1,60 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fmodulo-sched -fno-auto-inc-dec -O2 -fmodulo-sched-allow-regmoves" } */
+
+#include <stdlib.h>
+#include <stdarg.h>
+
+struct df_ref_info
+{
+  unsigned int *begin;
+  unsigned int *count;
+};
+
+extern void *memset (void *s, int c, __SIZE_TYPE__ n);
+
+
+__attribute__ ((noinline))
+int
+df_reorganize_refs_by_reg_by_insn (struct df_ref_info *ref_info,
+			           int num, unsigned int start)
+{
+  unsigned int m = num;
+  unsigned int offset = 77;
+  unsigned int r;
+
+  for (r = start; r < m; r++)
+    {
+      ref_info->begin[r] = offset;
+      offset += ref_info->count[r];
+      ref_info->count[r] = 0;
+    }
+
+  return offset;
+}
+
+int
+main ()
+{
+  struct df_ref_info temp;
+  int num = 100;
+  unsigned int start = 5;
+  int i, offset;
+
+  temp.begin = malloc (100 * sizeof (unsigned int));
+  temp.count = malloc (100 * sizeof (unsigned int));
+
+  memset (temp.begin, 0, sizeof (unsigned int) * num);
+  memset (temp.count, 0, sizeof (unsigned int) * num);
+
+  for (i = 0; i < num; i++)
+    temp.count[i] = i + 1;
+
+  offset = df_reorganize_refs_by_reg_by_insn (&temp, num, start);
+
+  if (offset != 5112)
+    abort ();
+
+  free (temp.begin);
+  free (temp.count);
+  return 0;
+}


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