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[PATCH] check alias sets in add_inter_loop_mem_dep (ddg.c)
- From: "Bingfeng Mei" <bmei at broadcom dot com>
- To: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Date: Thu, 15 Jan 2009 06:20:43 -0800
- Subject: [PATCH] check alias sets in add_inter_loop_mem_dep (ddg.c)
Hello,
I have a following patch to detect if memory references of two instructions belong to non-conflicting alias sets. It is used in inter-loop dependence analysis (ddg.c) by modulo scheduler. For the following testcase, GCC will produce better code due to better memory dependency info. In fact, powperpc-gcc cannot software pipeline this loop without the patch. OK for mainline? Should I also include this test in the patch?
/* {dg-do run} */
/* {dg-options "-O2 -fmodulo-sched -w"} */
void foo( int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
{
int i;
for(i = 0; i < 100; i+=4)
{
a[i] = b[i] * c[i];
a[i+1] = b[i+1] * c[i+1];
a[i+2] = b[i+2] * c[i+2];
a[i+3] = b[i+3] * c[i+3];
}
}
int a[100], b[100], c[100];
int main()
{
int i, res;
for(i = 0; i < 100; i++)
{
b[i] = c[i] = i;
}
foo(a, b, c);
res = 0;
for(i = 0; i < 100; i++)
{
res += a[i];
}
if(res != 328350)
abort();
return 0;
}
This is the first time I try to submit a patch. Hope it conforms to the coding style, patch format, etc. Additionally, my company (Broadcom) has already signed coporate copyright form with FSF.
Bingfeng Mei
Broadcom UK
2009-01-15 Bingfeng Mei <bmei@broadcom.com>
*alias.c (walk_mems_1, walk_mems_2, insn_alias_sets_conflict_p): Check
whether two instructions have memory references that belong to conflicting alias sets.
walk_mems_1 and walk_mems_2 are helper functions for traversing
*alias.h (insn_alias_sets_confilict_p): new prototypes
*ddg.c (add_inter_loop_mem_dep): call insn_alias_sets_conflict_p not to draw dependency edge
for instructions with non-conflicting alias sets.
Index: gcc/ddg.c
===================================================================
--- gcc/ddg.c (revision 143391)
+++ gcc/ddg.c (working copy)
@@ -345,6 +345,10 @@
static void
add_inter_loop_mem_dep (ddg_ptr g, ddg_node_ptr from, ddg_node_ptr to)
{
+ if (!insn_alias_sets_conflict_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))
Index: gcc/alias.c
===================================================================
--- gcc/alias.c (revision 143391)
+++ gcc/alias.c (working copy)
@@ -344,6 +344,43 @@
return 0;
}
+static int
+walk_mems_2 (rtx *x, rtx mem)
+{
+ if (MEM_P (*x))
+ {
+ if (alias_sets_conflict_p (MEM_ALIAS_SET(*x), MEM_ALIAS_SET(mem)))
+ return 1;
+
+ return -1;
+ }
+ return 0;
+}
+
+static int
+walk_mems_1 (rtx *x, rtx *pat)
+{
+ if (MEM_P (*x))
+ {
+ /* Visit all MEMs in *PAT and check indepedence. */
+ if (for_each_rtx (pat, (rtx_function) walk_mems_2, *x))
+ /* Indicate that dependence was determined and stop traversal. */
+ return 1;
+
+ return -1;
+ }
+ return 0;
+}
+
+/* Return 1 if two specified instructions have mem expr with conflict alias sets*/
+bool
+insn_alias_sets_conflict_p (rtx insn1, rtx insn2)
+{
+ /* For each pair of MEMs in INSN1 and INSN2 check their independence. */
+ return for_each_rtx (&PATTERN (insn1), (rtx_function) walk_mems_1,
+ &PATTERN (insn2));
+}
+
/* Return 1 if the two specified alias sets will always conflict. */
int
Index: gcc/alias.h
===================================================================
--- gcc/alias.h (revision 143391)
+++ gcc/alias.h (working copy)
@@ -41,6 +41,7 @@
extern int alias_sets_must_conflict_p (alias_set_type, alias_set_type);
extern int objects_must_conflict_p (tree, tree);
extern int nonoverlapping_memrefs_p (const_rtx, const_rtx);
+extern bool insn_alias_sets_conflict_p (rtx, rtx);
/* This alias set can be used to force a memory to conflict with all
other memories, creating a barrier across which no memory reference