Re: [PATCH] Clear variables with stale SSA_NAME_RANGE_INFO (PR tree-optimization/67690)

[Richard Biener <rguenther@suse.de>]

On September 25, 2015 3:49:34 PM GMT+02:00, Marek Polacek <polacek@redhat.com> wrote:
>On Fri, Sep 25, 2015 at 09:29:30AM +0200, Richard Biener wrote:
>> On Thu, 24 Sep 2015, Marek Polacek wrote:
>> 
>> > As Richi said in
><https://gcc.gnu.org/ml/gcc-patches/2015-01/msg02279.html>,
>> > using recorded SSA name range infos in VRP is likely to expose
>errors in the
>> > ranges.  This PR is such a case.  As discussed in the PR, after
>tail merging
>> > via PRE the range infos cannot be relied upon anymore, so we need
>to clear
>> > them.
>> > 
>> > Since tree-ssa-ifcombine.c already had code to clean up the flow
>data in a BB,
>> > I've factored it out to a common function.
>> > 
>> > Bootstrapped/regtested on x86_64-linux, ok for trunk and 5?
>> 
>> I believe for tail-merge you also need to clear range info on
>> PHI defs in the BB.  For ifcombine this wasn't necessary (no PHI
>nodes
>> in the relevant CFG), but it's ok to extend the new 
>> reset_flow_sensitive_info_in_bb function to also reset PHI defs.
>
>All right.
> 
>> Ok with that change.
>
>Since I'm not completely sure if I did the right thing here, could you
>please have another look at the new function?

Doesn't work that way.  You need to iterate over the PHI sequence separately via gsi_start_phis(bb), etc.

>Bootstrapped/regtested on x86_64-linux, ok for trunk/5?
>
>2015-09-25  Marek Polacek  <polacek@redhat.com>
>
>	PR tree-optimization/67690
>	* tree-ssa-ifcombine.c (pass_tree_ifcombine::execute): Call
>	reset_flow_sensitive_info_in_bb.
>	* tree-ssa-tail-merge.c (replace_block_by): Likewise.
>	* tree-ssanames.c: Include "gimple-iterator.h".
>	(reset_flow_sensitive_info_in_bb): New function.
>	* tree-ssanames.h (reset_flow_sensitive_info_in_bb): Declare.
>
>	* gcc.dg/torture/pr67690.c: New test.
>
>diff --git gcc/testsuite/gcc.dg/torture/pr67690.c
>gcc/testsuite/gcc.dg/torture/pr67690.c
>index e69de29..491de51 100644
>--- gcc/testsuite/gcc.dg/torture/pr67690.c
>+++ gcc/testsuite/gcc.dg/torture/pr67690.c
>@@ -0,0 +1,32 @@
>+/* { dg-do run } */
>+
>+const int c1 = 1;
>+const int c2 = 2;
>+
>+int
>+check (int i)
>+{
>+  int j;
>+  if (i >= 0)
>+    j = c2 - i;
>+  else
>+    j = c2 - i;
>+  return c2 - c1 + 1 > j;
>+}
>+
>+int invoke (int *pi) __attribute__ ((noinline,noclone));
>+int
>+invoke (int *pi)
>+{
>+  return check (*pi);
>+}
>+
>+int
>+main ()
>+{
>+  int i = c1;
>+  int ret = invoke (&i);
>+  if (!ret)
>+    __builtin_abort ();
>+  return 0;
>+}
>diff --git gcc/tree-ssa-ifcombine.c gcc/tree-ssa-ifcombine.c
>index 9f04174..66be430 100644
>--- gcc/tree-ssa-ifcombine.c
>+++ gcc/tree-ssa-ifcombine.c
>@@ -769,16 +769,7 @@ pass_tree_ifcombine::execute (function *fun)
> 	  {
> 	    /* Clear range info from all stmts in BB which is now executed
> 	       conditional on a always true/false condition.  */
>-	    for (gimple_stmt_iterator gsi = gsi_start_bb (bb);
>-		 !gsi_end_p (gsi); gsi_next (&gsi))
>-	      {
>-		gimple *stmt = gsi_stmt (gsi);
>-		ssa_op_iter i;
>-		tree op;
>-		FOR_EACH_SSA_TREE_OPERAND (op, stmt, i, SSA_OP_DEF)
>-		  reset_flow_sensitive_info (op);
>-	      }
>-
>+	    reset_flow_sensitive_info_in_bb (bb);
> 	    cfg_changed |= true;
> 	  }
>     }
>diff --git gcc/tree-ssa-tail-merge.c gcc/tree-ssa-tail-merge.c
>index 0ce59e8..487961e 100644
>--- gcc/tree-ssa-tail-merge.c
>+++ gcc/tree-ssa-tail-merge.c
>@@ -1534,6 +1534,10 @@ replace_block_by (basic_block bb1, basic_block
>bb2)
>       e2->probability = GCOV_COMPUTE_SCALE (e2->count, out_sum);
>     }
> 
>+  /* Clear range info from all stmts in BB2 -- this transformation
>+     could make them out of date.  */
>+  reset_flow_sensitive_info_in_bb (bb2);
>+
>   /* Do updates that use bb1, before deleting bb1.  */
>   release_last_vdef (bb1);
>   same_succ_flush_bb (bb1);
>diff --git gcc/tree-ssanames.c gcc/tree-ssanames.c
>index 4199290..ef21137 100644
>--- gcc/tree-ssanames.c
>+++ gcc/tree-ssanames.c
>@@ -23,6 +23,7 @@ along with GCC; see the file COPYING3.  If not see
> #include "backend.h"
> #include "tree.h"
> #include "gimple.h"
>+#include "gimple-iterator.h"
> #include "hard-reg-set.h"
> #include "ssa.h"
> #include "alias.h"
>@@ -544,6 +545,27 @@ reset_flow_sensitive_info (tree name)
>     SSA_NAME_RANGE_INFO (name) = NULL;
> }
> 
>+/* Clear all flow sensitive data from all statements and PHI
>definitions
>+   in BB.  */
>+
>+void
>+reset_flow_sensitive_info_in_bb (basic_block bb)
>+{
>+  for (gimple_stmt_iterator gsi = gsi_start_bb (bb); !gsi_end_p (gsi);
>+       gsi_next (&gsi))
>+    {
>+      gimple *stmt = gsi_stmt (gsi);
>+      ssa_op_iter i;
>+      def_operand_p def;
>+      FOR_EACH_PHI_OR_STMT_DEF (def, stmt, i, SSA_OP_DEF)
>+	{
>+	  tree var = DEF_FROM_PTR (def);
>+	  if (TREE_CODE (var) != SSA_NAME)
>+	    continue;
>+	  reset_flow_sensitive_info (var);
>+	}
>+    }
>+}
> 
> /* Release all the SSA_NAMEs created by STMT.  */
> 
>diff --git gcc/tree-ssanames.h gcc/tree-ssanames.h
>index 22ff609..5688ca5 100644
>--- gcc/tree-ssanames.h
>+++ gcc/tree-ssanames.h
>@@ -95,6 +95,7 @@ extern tree duplicate_ssa_name_fn (struct function *,
>tree, gimple *);
>extern void duplicate_ssa_name_range_info (tree, enum value_range_type,
> 					   struct range_info_def *);
> extern void reset_flow_sensitive_info (tree);
>+extern void reset_flow_sensitive_info_in_bb (basic_block);
> extern void release_defs (gimple *);
> extern void replace_ssa_name_symbol (tree, tree);
> 
>
>	Marek