PHIOPT: Mark the conditional lhs and rhs as to look at to see if DCEable

In some cases (usually dealing with bools only), there could be some statements
left behind which are considered trivial dead.
An example is:
```
bool f(bool a, bool b)
{
    if (!a && !b)
        return 0;
    if (!a && b)
        return 0;
    if (a && !b)
        return 0;
    return 1;
}
```
Where during phiopt2, the IR had:
```
  _3 = ~b_7(D);
  _4 = _3 & a_6(D);
  _4 != 0 ? 0 : 1
```
match-and-simplify would transform that into:
```
  _11 = ~a_6(D);
  _12 = b_7(D) | _11;
```
But phiopt would leave around the statements defining _4 and _3.
This helps by marking the conditional's lhs and rhs to see if they are
trivial dead.

OK? Bootstrapped and tested on x86_64-linux-gnu.

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (match_simplify_replacement): Mark's cond
	statement's lhs and rhs to check if trivial dead.
	Rename inserted_exprs to exprs_maybe_dce; also move it so
	bitmap is not allocated if not needed.

diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index cb4e2da023dd91da687e49f9ad424d251d31958b..ff36bb0119b5a73db416083d0e1d05d8c18259ce 100644 (file)
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -767,7 +767,6 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
   tree result;
   gimple *stmt_to_move = NULL;
   gimple *stmt_to_move_alt = NULL;
-  auto_bitmap inserted_exprs;
   tree arg_true, arg_false;
 
   /* Special case A ? B : B as this will always simplify to B. */
@@ -844,6 +843,18 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
   if (!result)
     return false;
 
+  auto_bitmap exprs_maybe_dce;
+
+  /* Mark the cond statements' lhs/rhs as maybe dce.  */
+  if (TREE_CODE (gimple_cond_lhs (stmt)) == SSA_NAME
+      && !SSA_NAME_IS_DEFAULT_DEF (gimple_cond_lhs (stmt)))
+    bitmap_set_bit (exprs_maybe_dce,
+                   SSA_NAME_VERSION (gimple_cond_lhs (stmt)));
+  if (TREE_CODE (gimple_cond_rhs (stmt)) == SSA_NAME
+      && !SSA_NAME_IS_DEFAULT_DEF (gimple_cond_rhs (stmt)))
+    bitmap_set_bit (exprs_maybe_dce,
+                   SSA_NAME_VERSION (gimple_cond_rhs (stmt)));
+
   gsi = gsi_last_bb (cond_bb);
   /* Insert the sequence generated from gimple_simplify_phiopt.  */
   if (seq)
@@ -855,7 +866,7 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
          gimple *stmt = gsi_stmt (gsi1);
          tree name = gimple_get_lhs (stmt);
          if (name && TREE_CODE (name) == SSA_NAME)
-           bitmap_set_bit (inserted_exprs, SSA_NAME_VERSION (name));
+           bitmap_set_bit (exprs_maybe_dce, SSA_NAME_VERSION (name));
        }
       if (dump_file && (dump_flags & TDF_FOLDING))
        {
@@ -867,10 +878,10 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
 
   /* If there was a statement to move, move it to right before
      the original conditional.  */
-  move_stmt (stmt_to_move, &gsi, inserted_exprs);
-  move_stmt (stmt_to_move_alt, &gsi, inserted_exprs);
+  move_stmt (stmt_to_move, &gsi, exprs_maybe_dce);
+  move_stmt (stmt_to_move_alt, &gsi, exprs_maybe_dce);
 
-  replace_phi_edge_with_variable (cond_bb, e1, phi, result, inserted_exprs);
+  replace_phi_edge_with_variable (cond_bb, e1, phi, result, exprs_maybe_dce);
 
   /* Add Statistic here even though replace_phi_edge_with_variable already
      does it as we want to be able to count when match-simplify happens vs