Re: [PR69123] fix VTA dataflow oscillation

[Alexandre Oliva <aoliva at redhat dot com>]

On Jan  9, 2016, Alexandre Oliva <aoliva@redhat.com> wrote:

> for gcc/testsuite/ChangeLog

> 	PR bootstrap/69123
> 	* gcc.dg/pr69123.c: New.

Doh, it doesn't work to install a C++ testcase as C.  Here's the patch
with testcase that I actually tested successfully and checked in.


[PR69123] fix handling of MEMs in VTA to avoid dataflow oscillation

From: Alexandre Oliva <aoliva@redhat.com>

The problem arises because we used to drop overwritten MEMs from loc
lists of VALUEs, but not of other onepart variables, and it just so
happens that, by doing so, block 6 in the testcase has no D#5 in its
output in the first pass, because the MEM holding its (previous) value
was correctly dropped from value 88:88, but gains it in the second
pass because D#5 has the MEM location incoming directly in its loc
list, rather than indirectly in a VALUE.

This incorrect binding enables other blocks to believe they have a
tentative binding for D#5 in some cycles, but others, still operating
on the early conclusion, believe there isn't, and they oscillate from
that.

Since we check for escaping MEMs in clobbers, we won't lose anything
relevant by dropping call-clobbered or overwritten MEMs in all onepart
variables, and this ensures the loc intersection operation in onepart
vars won't let a MEM through that wasn't present in earlier
iterations.

for  gcc/ChangeLog

	PR bootstrap/69123
	* var-tracking.c (drop_overlapping_mem_locs): Operate on all
	onepart vars.  Fix typo in comment.  Fix reversed condition in
	unshare test.
	(dataflow_set_remove_mem_locs): Operate on all onepart vars.

for gcc/testsuite/ChangeLog

	PR bootstrap/69123
	* g++.dg/pr69123.C: New.
---
 gcc/testsuite/g++.dg/pr69123.C |   95 ++++++++++++++++++++++++++++++++++++++++
 gcc/var-tracking.c             |   12 +++--
 2 files changed, 101 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/pr69123.C

diff --git a/gcc/testsuite/g++.dg/pr69123.C b/gcc/testsuite/g++.dg/pr69123.C
new file mode 100644
index 0000000..0546e20
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr69123.C
@@ -0,0 +1,95 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -g" } */
+
+/* This was reduced from gcc/tree-vect-slp.c by H.J.Lu.  */
+
+struct xxx_def;
+typedef xxx_def *xxx;
+
+union rtxxx
+{
+  const char *rt_str;
+  xxx rt_xxx;
+};
+
+struct xxx_def {
+  union u {
+    rtxxx fld[1];
+  } u;
+};
+
+extern xxx bar (void);
+extern int foo1 (xxx);
+
+static inline xxx
+foo2 (xxx arg0, xxx arg1)
+{
+  xxx rt;
+  rt = bar ();
+  (((rt)->u.fld[0]).rt_xxx) = arg0;
+  (((rt)->u.fld[1]).rt_xxx) = arg1;
+  return rt;
+}
+
+static inline xxx
+foo4 (const char *arg0 )
+{
+  xxx rt;
+  rt = bar ();
+  (((rt)->u.fld[0]).rt_str) = arg0;
+  (((rt)->u.fld[1]).rt_xxx) = (xxx) 0;
+  return rt;
+}
+
+extern xxx foo5 (long);
+
+struct address_cost_data
+{
+  unsigned costs[2][2][2][2];
+};
+
+void
+get_address_cost (address_cost_data *data)
+{
+  unsigned acost;
+  long i;
+  long rat, off = 0;
+  unsigned sym_p, var_p, off_p, rat_p;
+  xxx addr, base;
+  xxx reg0, reg1;
+
+  reg1 = bar ();
+  addr = foo2 (reg1, (xxx) 0);
+  rat = 1;
+  acost = 0;
+  reg0 = bar ();
+  reg1 = bar ();
+
+  for (i = 0; i < 16; i++)
+    {
+      sym_p = i & 1;
+      var_p = (i >> 1) & 1;
+      off_p = (i >> 2) & 1;
+      rat_p = (i >> 3) & 1;
+
+      addr = reg0;
+      if (rat_p)
+	addr = foo2 (addr, foo5 (rat)) ;
+
+      if (var_p)
+	addr = foo2 (addr, reg1);
+
+      if (sym_p)
+	base = foo4 ("");
+      else if (off_p)
+	base = foo5 (off);
+      else
+	base = (xxx) 0;
+
+      if (base)
+	addr = foo2 (addr, base);
+
+      acost = foo1 (addr);
+      data->costs[sym_p][var_p][off_p][rat_p] = acost;
+    }
+}
diff --git a/gcc/var-tracking.c b/gcc/var-tracking.c
index 023a73e..86183b3 100644
--- a/gcc/var-tracking.c
+++ b/gcc/var-tracking.c
@@ -2224,7 +2224,7 @@ struct overlapping_mems
 };
 
 /* Remove all MEMs that overlap with COMS->LOC from the location list
-   of a hash table entry for a value.  COMS->ADDR must be a
+   of a hash table entry for a onepart variable.  COMS->ADDR must be a
    canonicalized form of COMS->LOC's address, and COMS->LOC must be
    canonicalized itself.  */
 
@@ -2235,7 +2235,7 @@ drop_overlapping_mem_locs (variable **slot, overlapping_mems *coms)
   rtx mloc = coms->loc, addr = coms->addr;
   variable *var = *slot;
 
-  if (var->onepart == ONEPART_VALUE)
+  if (var->onepart != NOT_ONEPART)
     {
       location_chain *loc, **locp;
       bool changed = false;
@@ -4682,11 +4682,11 @@ dataflow_set_preserve_mem_locs (variable **slot, dataflow_set *set)
 	{
 	  for (loc = var->var_part[0].loc_chain; loc; loc = loc->next)
 	    {
-	      /* We want to remove dying MEMs that doesn't refer to DECL.  */
+	      /* We want to remove dying MEMs that don't refer to DECL.  */
 	      if (GET_CODE (loc->loc) == MEM
 		  && (MEM_EXPR (loc->loc) != decl
 		      || INT_MEM_OFFSET (loc->loc) != 0)
-		  && !mem_dies_at_call (loc->loc))
+		  && mem_dies_at_call (loc->loc))
 		break;
 	      /* We want to move here MEMs that do refer to DECL.  */
 	      else if (GET_CODE (loc->loc) == VALUE
@@ -4769,14 +4769,14 @@ dataflow_set_preserve_mem_locs (variable **slot, dataflow_set *set)
 }
 
 /* Remove all MEMs from the location list of a hash table entry for a
-   value.  */
+   onepart variable.  */
 
 int
 dataflow_set_remove_mem_locs (variable **slot, dataflow_set *set)
 {
   variable *var = *slot;
 
-  if (var->onepart == ONEPART_VALUE)
+  if (var->onepart != NOT_ONEPART)
     {
       location_chain *loc, **locp;
       bool changed = false;


-- 
Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/   FSF Latin America board member
Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer