[PATCH 2/2] [PHIOPT/MATCH] Remove the statement to move if not used

[apinski--- via Gcc-patches]

From: Andrew Pinski <apin...@marvell.com>

Instead of waiting for DCE to remove the unused statement,
and maybe optimize another conditional, it is better if
we don't move the statement and have the statement
removed.

gcc/ChangeLog:

        * tree-ssa-phiopt.c (used_in_seq): New function.
        (match_simplify_replacement): Don't move the statement
        if not used in sequence.

gcc/testsuite/ChangeLog:

        * gcc.dg/tree-ssa/pr96928-1.c: Update to similar as pr96928.c.
---
 gcc/testsuite/gcc.dg/tree-ssa/pr96928-1.c |  5 ++++-
 gcc/tree-ssa-phiopt.c                     | 24 ++++++++++++++++++++++-
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr96928-1.c 
b/gcc/testsuite/gcc.dg/tree-ssa/pr96928-1.c
index 2e86620da11..9e505ac9900 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr96928-1.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr96928-1.c
@@ -2,7 +2,10 @@
 /* { dg-do compile } */
 /* { dg-options "-O2 -fdump-tree-phiopt2 -fdump-tree-optimized" } */
 /* { dg-final { scan-tree-dump-times " = a_\[0-9]*\\\(D\\\) >> " 5 "phiopt2" } 
} */
-/* { dg-final { scan-tree-dump-times " = ~c_\[0-9]*\\\(D\\\);" 1 "phiopt2" } } 
*/
+/* The following check is done at optimized because a ^ (~b) is rewritten as 
~(a^b)
+   and in the case of match.pd optimizing these ?:, the ~ is moved out already
+   by the time we get to phiopt2. */
+/* { dg-final { scan-tree-dump-times "c_\[0-9]*\\\(D\\\) \\\^" 1 "optimized" } 
} */
 /* { dg-final { scan-tree-dump-times " = ~" 1 "optimized" } } */
 /* { dg-final { scan-tree-dump-times " = \[abc_0-9\\\(\\\)D]* \\\^ " 5 
"phiopt2" } } */
 /* { dg-final { scan-tree-dump-not "a < 0" "phiopt2" } } */
diff --git a/gcc/tree-ssa-phiopt.c b/gcc/tree-ssa-phiopt.c
index 7a98b7afdf1..a237df02153 100644
--- a/gcc/tree-ssa-phiopt.c
+++ b/gcc/tree-ssa-phiopt.c
@@ -934,6 +934,26 @@ gimple_simplify_phiopt (bool early_p, tree type, gimple 
*comp_stmt,
   return NULL;
 }
 
+/* Return true if the lhs of STMT is used in the SEQ sequence
+   of statements.  */
+static bool
+used_in_seq (gimple *stmt, gimple_seq seq)
+{
+  tree lhs = gimple_assign_lhs (stmt);
+  for (auto gsi = gsi_start (seq); !gsi_end_p (gsi); gsi_next_nondebug (&gsi))
+    {
+      use_operand_p use_p;
+      ssa_op_iter iter;
+      gimple *stmt1 = gsi_stmt (gsi);
+      FOR_EACH_SSA_USE_OPERAND (use_p, stmt1, iter, SSA_OP_USE)
+       {
+         if (USE_FROM_PTR (use_p) == lhs)
+           return true;
+       }
+    }
+    return false;
+}
+
 /*  The function match_simplify_replacement does the main work of doing the
     replacement using match and simplify.  Return true if the replacement is 
done.
     Otherwise return false.
@@ -1020,7 +1040,9 @@ match_simplify_replacement (basic_block cond_bb, 
basic_block middle_bb,
     return false;
 
   gsi = gsi_last_bb (cond_bb);
-  if (stmt_to_move)
+  if (stmt_to_move
+      && (gimple_assign_lhs (stmt_to_move) == result
+          || used_in_seq (stmt_to_move, seq)))
     {
       if (dump_file && (dump_flags & TDF_DETAILS))
        {
-- 
2.27.0