PHI-OPT: speed up value_replacement slightly

This adds a few early outs to value_replacement that I noticed
while rewriting this to use match-and-simplify but could be committed
seperately.
* virtual operands won't change so return early for them
* special case `A ? B : B` as that is already just `B`

Also moves the check for NE/EQ earlier as calculating empty_or_with_defined_p
is an IR walk for a BB and that might be big.

Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (value_replacement): Move check for
	NE/EQ earlier.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index f1e07502b02d01c5a83faa5706aff7dbe4273d21..a2bdcb5eae81d43054a5fd833c6ba11ba9ebb27f 100644 (file)
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -1131,6 +1131,21 @@ value_replacement (basic_block cond_bb, basic_block middle_bb,
   enum tree_code code;
   bool empty_or_with_defined_p = true;
 
+  /* Virtual operands don't need to be handled. */
+  if (virtual_operand_p (arg1))
+    return 0;
+
+  /* Special case A ? B : B as this will always simplify to B. */
+  if (operand_equal_for_phi_arg_p (arg0, arg1))
+    return 0;
+
+  gcond *cond = as_a <gcond *> (*gsi_last_bb (cond_bb));
+  code = gimple_cond_code (cond);
+
+  /* This transformation is only valid for equality comparisons.  */
+  if (code != NE_EXPR && code != EQ_EXPR)
+    return 0;
+
   /* If the type says honor signed zeros we cannot do this
      optimization.  */
   if (HONOR_SIGNED_ZEROS (arg1))
@@ -1161,13 +1176,6 @@ value_replacement (basic_block cond_bb, basic_block middle_bb,
        empty_or_with_defined_p = false;
     }
 
-  gcond *cond = as_a <gcond *> (*gsi_last_bb (cond_bb));
-  code = gimple_cond_code (cond);
-
-  /* This transformation is only valid for equality comparisons.  */
-  if (code != NE_EXPR && code != EQ_EXPR)
-    return 0;
-
   /* We need to know which is the true edge and which is the false
       edge so that we know if have abs or negative abs.  */
   extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);