On Wed, May 05, 2021 at 01:39:32PM +0200, Richard Biener wrote:
> Can you in the above IL snippets mark COND_BB and MIDDLE_BB?
...

Thanks.
Here is an updated patch (attached) and interdiff from previous patch.
Ok for trunk if it passes bootstrap/regtest?

--- gcc/tree-ssa-phiopt.c	2021-05-03 17:49:54.233300624 +0200
+++ gcc/tree-ssa-phiopt.c	2021-05-05 15:06:23.253189139 +0200
@@ -65,7 +65,7 @@
 static bool xor_replacement (basic_block, basic_block,
 			     edge, edge, gimple *, tree, tree);
 static bool spaceship_replacement (basic_block, basic_block,
-				   edge, edge, gimple *, tree, tree);
+				   edge, edge, gphi *, tree, tree);
 static bool cond_removal_in_popcount_clz_ctz_pattern (basic_block, basic_block,
 						      edge, edge, gimple *,
 						      tree, tree);
@@ -1840,53 +1840,53 @@
 
 /* Attempt to optimize (x <=> y) cmp 0 and similar comparisons.
    For strong ordering <=> try to match something like:
-    <bb 2> :
+    <bb 2> :  // cond3_bb (== cond2_bb)
     if (x_4(D) != y_5(D))
       goto <bb 3>; [INV]
     else
       goto <bb 6>; [INV]
 
-    <bb 3> :
+    <bb 3> :  // cond_bb
     if (x_4(D) < y_5(D))
       goto <bb 6>; [INV]
     else
       goto <bb 4>; [INV]
 
-    <bb 4> :
+    <bb 4> :  // middle_bb
 
-    <bb 6> :
+    <bb 6> :  // phi_bb
     # iftmp.0_2 = PHI <1(4), 0(2), -1(3)>
     _1 = iftmp.0_2 == 0;
 
    and for partial ordering <=> something like:
 
-    <bb 2> :
+    <bb 2> :  // cond3_bb
     if (a_3(D) == b_5(D))
       goto <bb 6>; [50.00%]
     else
       goto <bb 3>; [50.00%]
 
-    <bb 3> [local count: 536870913]:
+    <bb 3> [local count: 536870913]:  // cond2_bb
     if (a_3(D) < b_5(D))
       goto <bb 6>; [50.00%]
     else
       goto <bb 4>; [50.00%]
 
-    <bb 4> [local count: 268435456]:
+    <bb 4> [local count: 268435456]:  // cond_bb
     if (a_3(D) > b_5(D))
       goto <bb 6>; [50.00%]
     else
       goto <bb 5>; [50.00%]
 
-    <bb 5> [local count: 134217728]:
+    <bb 5> [local count: 134217728]:  // middle_bb
 
-    <bb 6> [local count: 1073741824]:
+    <bb 6> [local count: 1073741824]:  // phi_bb
     # SR.27_4 = PHI <0(2), -1(3), 1(4), 2(5)>
     _2 = SR.27_4 > 0;  */
 
 static bool
 spaceship_replacement (basic_block cond_bb, basic_block middle_bb,
-		       edge e0, edge e1, gimple *phi,
+		       edge e0, edge e1, gphi *phi,
 		       tree arg0, tree arg1)
 {
   if (!INTEGRAL_TYPE_P (TREE_TYPE (PHI_RESULT (phi)))
@@ -1897,6 +1897,11 @@
       || !IN_RANGE (tree_to_shwi (arg1), -1, 2))
     return false;
 
+  basic_block phi_bb = gimple_bb (phi);
+  gcc_assert (phi_bb == e0->dest && phi_bb == e1->dest);
+  if (!IN_RANGE (EDGE_COUNT (phi_bb->preds), 3, 4))
+    return false;
+
   use_operand_p use_p;
   gimple *use_stmt;
   if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (PHI_RESULT (phi)))
@@ -1953,11 +1958,6 @@
   if (!empty_block_p (middle_bb))
     return false;
 
-  basic_block phi_bb = gimple_bb (phi);
-  gcc_assert (phi_bb == e0->dest && phi_bb == e1->dest);
-  if (!IN_RANGE (EDGE_COUNT (phi_bb->preds), 3, 4))
-    return false;
-
   gcond *cond1 = as_a <gcond *> (last_stmt (cond_bb));
   enum tree_code cmp1 = gimple_cond_code (cond1);
   if (cmp1 != LT_EXPR && cmp1 != GT_EXPR)
@@ -1965,7 +1965,7 @@
   tree lhs1 = gimple_cond_lhs (cond1);
   tree rhs1 = gimple_cond_rhs (cond1);
   /* The optimization may be unsafe due to NaNs.  */
-  if (HONOR_NANS (TREE_TYPE (lhs1)) || HONOR_SIGNED_ZEROS (TREE_TYPE (lhs1)))
+  if (HONOR_NANS (TREE_TYPE (lhs1)))
     return false;
   if (TREE_CODE (lhs1) == SSA_NAME && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (lhs1))
     return false;
@@ -2180,11 +2180,6 @@
       gimple_assign_set_rhs1 (use_stmt, cond);
     }
   update_stmt (use_stmt);
-  if (cmp3 == EQ_EXPR)
-    gimple_cond_make_true (as_a <gcond *> (cond3));
-  else
-    gimple_cond_make_false (as_a <gcond *> (cond3));
-  update_stmt (cond3);
 
   if (MAY_HAVE_DEBUG_BIND_STMTS)
     {
@@ -2201,6 +2196,13 @@
 
       if (has_debug_uses)
 	{
+	  /* If there are debug uses, emit something like:
+	     # DEBUG D#1 => i_2(D) > j_3(D) ? 1 : -1
+	     # DEBUG D#2 => i_2(D) == j_3(D) ? 0 : D#1
+	     where > stands for the comparison that yielded 1
+	     and replace debug uses of phi result with that D#2.
+	     Ignore the value of 2, because if NaNs aren't expected,
+	     all floating point numbers should be comparable.  */
 	  gimple_stmt_iterator gsi = gsi_after_labels (gimple_bb (phi));
 	  tree type = TREE_TYPE (PHI_RESULT (phi));
 	  tree temp1 = make_node (DEBUG_EXPR_DECL);
@@ -2224,6 +2226,9 @@
 	}
     }
 
+  gimple_stmt_iterator psi = gsi_for_stmt (phi);
+  remove_phi_node (&psi, true);
+
   return true;
 }
 


	Jakub