Hi All,

This patch adds support for three-way min/max recognition in phi-opts.

Concretely for e.g.

#include <stdint.h>

uint8_t three_min (uint8_t xc, uint8_t xm, uint8_t xy) {
	uint8_t	 xk;
    if (xc < xm) {
        xk = (uint8_t) (xc < xy ? xc : xy);
    } else {
        xk = (uint8_t) (xm < xy ? xm : xy);
    }
    return xk;
}

we generate:

  <bb 2> [local count: 1073741824]:
  _5 = MIN_EXPR <xc_1(D), xy_3(D)>;
  _7 = MIN_EXPR <xm_2(D), _5>;
  return _7;

instead of

  <bb 2>:
  if (xc_2(D) < xm_3(D))
    goto <bb 3>;
  else
    goto <bb 4>;

  <bb 3>:
  xk_5 = MIN_EXPR <xc_2(D), xy_4(D)>;
  goto <bb 5>;

  <bb 4>:
  xk_6 = MIN_EXPR <xm_3(D), xy_4(D)>;

  <bb 5>:
  # xk_1 = PHI <xk_5(3), xk_6(4)>
  return xk_1;

The same function also immediately deals with turning a minimization problem
into a maximization one if the results are inverted.  We do this here since
doing it in match.pd would end up changing the shape of the BBs and adding
additional instructions which would prevent various optimizations from working.

Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.

Ok for master?

Thanks,
Tamar

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (minmax_replacement): Optionally search for the phi
	sequence of a three-way conditional.
	(replace_phi_edge_with_variable): Support deferring of BB removal.
	(tree_ssa_phiopt_worker): Detect diamond phi structure for three-way
	min/max.
	(strip_bit_not, invert_minmax_code): New.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/split-path-1.c: Disable phi-opts so we don't optimize
	code away.
	* gcc.dg/tree-ssa/minmax-3.c: New test.
	* gcc.dg/tree-ssa/minmax-4.c: New test.
	* gcc.dg/tree-ssa/minmax-5.c: New test.
	* gcc.dg/tree-ssa/minmax-6.c: New test.
	* gcc.dg/tree-ssa/minmax-7.c: New test.
	* gcc.dg/tree-ssa/minmax-8.c: New test.

--- inline copy of patch -- 
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-3.c b/gcc/testsuite/gcc.dg/tree-ssa/minmax-3.c
new file mode 100644
index 0000000000000000000000000000000000000000..de3b2e946e81701e3b75f580e6a843695a05786e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-3.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-phiopt" } */
+
+#include <stdint.h>
+
+uint8_t three_min (uint8_t xc, uint8_t xm, uint8_t xy) {
+	uint8_t	 xk;
+    if (xc < xm) {
+        xk = (uint8_t) (xc < xy ? xc : xy);
+    } else {
+        xk = (uint8_t) (xm < xy ? xm : xy);
+    }
+    return xk;
+}
+
+/* { dg-final { scan-tree-dump-times "MIN_EXPR" 3 "phiopt1" } } */
+/* { dg-final { scan-tree-dump-times "MAX_EXPR" 0 "phiopt1" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-4.c b/gcc/testsuite/gcc.dg/tree-ssa/minmax-4.c
new file mode 100644
index 0000000000000000000000000000000000000000..0b6d667be868c2405eaefd17cb522da44bafa0e2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-4.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-phiopt" } */
+
+#include <stdint.h>
+
+uint8_t three_max (uint8_t xc, uint8_t xm, uint8_t xy) {
+    uint8_t	 xk;
+    if (xc > xm) {
+        xk = (uint8_t) (xc > xy ? xc : xy);
+    } else {
+        xk = (uint8_t) (xm > xy ? xm : xy);
+    }
+    return xk;
+}
+
+/* { dg-final { scan-tree-dump-times "MIN_EXPR" 0 "phiopt1" } } */
+/* { dg-final { scan-tree-dump-times "MAX_EXPR" 3 "phiopt1" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-5.c b/gcc/testsuite/gcc.dg/tree-ssa/minmax-5.c
new file mode 100644
index 0000000000000000000000000000000000000000..650601a3cc75d09a9e6e54a35f5b9993074f8510
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-5.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-phiopt" } */
+
+#include <stdint.h>
+
+uint8_t three_minmax1 (uint8_t xc, uint8_t xm, uint8_t xy) {
+	uint8_t	 xk;
+    if (xc > xm) {
+        xk = (uint8_t) (xc < xy ? xc : xy);
+    } else {
+        xk = (uint8_t) (xm < xy ? xm : xy);
+    }
+    return xk;
+}
+
+/* { dg-final { scan-tree-dump-times "MIN_EXPR" 2 "phiopt1" } } */
+/* { dg-final { scan-tree-dump-times "MAX_EXPR" 1 "phiopt1" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-6.c b/gcc/testsuite/gcc.dg/tree-ssa/minmax-6.c
new file mode 100644
index 0000000000000000000000000000000000000000..a628f6d99222958cfd8c410f0e85639e3a49dd4b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-6.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-phiopt" } */
+
+#include <stdint.h>
+
+uint8_t three_minmax3 (uint8_t xc, uint8_t xm, uint8_t xy) {
+        uint8_t  xk;
+    if (xc > xm) {
+        xk = (uint8_t) (xy < xc ? xc : xy);
+    } else {
+        xk = (uint8_t) (xm < xy ? xm : xy);
+    }
+    return xk;
+}
+
+/* { dg-final { scan-tree-dump-times "MIN_EXPR" 1 "phiopt1" } } */
+/* { dg-final { scan-tree-dump-times "MAX_EXPR" 1 "phiopt1" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-7.c b/gcc/testsuite/gcc.dg/tree-ssa/minmax-7.c
new file mode 100644
index 0000000000000000000000000000000000000000..cb42412c4ada433b2f59df0a8bef9fa7b1c5e104
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-7.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-phiopt" } */
+
+#include <stdint.h>
+
+uint8_t three_minmax2 (uint8_t xc, uint8_t xm, uint8_t xy) {
+	uint8_t	 xk;
+    if (xc > xm) {
+        xk = (uint8_t) (xc > xy ? xc : xy);
+    } else {
+        xk = (uint8_t) (xm < xy ? xm : xy);
+    }
+    return xk;
+}
+/* { dg-final { scan-tree-dump-times "MIN_EXPR" 1 "phiopt1" } } */
+/* { dg-final { scan-tree-dump-times "MAX_EXPR" 1 "phiopt1" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-8.c b/gcc/testsuite/gcc.dg/tree-ssa/minmax-8.c
new file mode 100644
index 0000000000000000000000000000000000000000..9cd050e932376bc50bd6ae60cb654fcab0bfdd1c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-8.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-phiopt" } */
+
+#include <stdint.h>
+
+uint8_t three_minmax11 (uint8_t xc, uint8_t xm, uint8_t xy) {
+        uint8_t  xk;
+    if (xc < xm) {
+        xk = (uint8_t) (xc > xy ? xc : xy);
+    } else {
+        xk = (uint8_t) (xm > xy ? xm : xy);
+    }
+    return xk;
+}
+
+/* { dg-final { scan-tree-dump-times "MIN_EXPR" 1 "phiopt1" } } */
+/* { dg-final { scan-tree-dump-times "MAX_EXPR" 2 "phiopt1" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/split-path-1.c b/gcc/testsuite/gcc.dg/tree-ssa/split-path-1.c
index 8b23ef4c7a3484cdc1647ee6d1b150f15685beff..902dde44a50e171b4f34ba7247d75a32d2c860ed 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/split-path-1.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/split-path-1.c
@@ -1,5 +1,5 @@
 /* { dg-do run } */
-/* { dg-options "-O2 -fsplit-paths -fdump-tree-split-paths-details --param max-jump-thread-duplication-stmts=20" } */
+/* { dg-options "-O2 -fsplit-paths -fdump-tree-split-paths-details --param max-jump-thread-duplication-stmts=20 -fno-ssa-phiopt" } */
 
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index 562468b7f02a9ffe2713318add551902c14f89c3..6246f054006ff16e73602e7ce2e367d2d21421b1 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -62,8 +62,8 @@ static gphi *factor_out_conditional_conversion (edge, edge, gphi *, tree, tree,
 						gimple *);
 static int value_replacement (basic_block, basic_block,
 			      edge, edge, gphi *, tree, tree);
-static bool minmax_replacement (basic_block, basic_block,
-				edge, edge, gphi *, tree, tree);
+static bool minmax_replacement (basic_block, basic_block, basic_block,
+				edge, edge, gphi *, tree, tree, bool);
 static bool spaceship_replacement (basic_block, basic_block,
 				   edge, edge, gphi *, tree, tree);
 static bool cond_removal_in_builtin_zero_pattern (basic_block, basic_block,
@@ -73,7 +73,7 @@ static bool cond_store_replacement (basic_block, basic_block, edge, edge,
 				    hash_set<tree> *);
 static bool cond_if_else_store_replacement (basic_block, basic_block, basic_block);
 static hash_set<tree> * get_non_trapping ();
-static void replace_phi_edge_with_variable (basic_block, edge, gphi *, tree);
+static void replace_phi_edge_with_variable (basic_block, edge, gphi *, tree, bool);
 static void hoist_adjacent_loads (basic_block, basic_block,
 				  basic_block, basic_block);
 static bool gate_hoist_loads (void);
@@ -199,6 +199,7 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads, bool early_p)
       basic_block bb1, bb2;
       edge e1, e2;
       tree arg0, arg1;
+      bool diamond_minmax_p = false;
 
       bb = bb_order[i];
 
@@ -265,6 +266,29 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads, bool early_p)
 	    hoist_adjacent_loads (bb, bb1, bb2, bb3);
 	  continue;
 	}
+      else if (EDGE_SUCC (bb1, 0)->dest == EDGE_SUCC (bb2, 0)->dest
+	       && single_succ_p (bb1)
+	       && single_succ_p (bb2)
+	       && single_pred_p (bb1)
+	       && single_pred_p (bb2)
+	       && single_succ_p (EDGE_SUCC (bb1, 0)->dest))
+	{
+	  gimple_stmt_iterator it1 = gsi_start_nondebug_after_labels_bb (bb1);
+	  gimple_stmt_iterator it2 = gsi_start_nondebug_after_labels_bb (bb2);
+	  if (gsi_one_before_end_p (it1) && gsi_one_before_end_p (it2))
+	    {
+	      gimple *stmt1 = gsi_stmt (it1);
+	      gimple *stmt2 = gsi_stmt (it2);
+	      if (is_gimple_assign (stmt1) && is_gimple_assign (stmt2))
+		{
+		  enum tree_code code1 = gimple_assign_rhs_code (stmt1);
+		  enum tree_code code2 = gimple_assign_rhs_code (stmt2);
+		  diamond_minmax_p
+		    = (code1 == MIN_EXPR || code1 == MAX_EXPR)
+		      && (code2 == MIN_EXPR || code2 == MAX_EXPR);
+		}
+	    }
+	}
       else
 	continue;
 
@@ -316,6 +340,13 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads, bool early_p)
 	  if (!candorest)
 	    continue;
 
+	  /* Check that we're looking for nested phis.  */
+	  if (phis == NULL && diamond_minmax_p)
+	    {
+	      phis = phi_nodes (EDGE_SUCC (bb2, 0)->dest);
+	      e2 = EDGE_SUCC (bb2, 0);
+	    }
+
 	  phi = single_non_singleton_phi_for_edges (phis, e1, e2);
 	  if (!phi)
 	    continue;
@@ -329,6 +360,7 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads, bool early_p)
 
 	  gphi *newphi;
 	  if (single_pred_p (bb1)
+	      && !diamond_minmax_p
 	      && (newphi = factor_out_conditional_conversion (e1, e2, phi,
 							      arg0, arg1,
 							      cond_stmt)))
@@ -343,20 +375,25 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads, bool early_p)
 	    }
 
 	  /* Do the replacement of conditional if it can be done.  */
-	  if (!early_p && two_value_replacement (bb, bb1, e2, phi, arg0, arg1))
+	  if (!early_p
+	      && !diamond_minmax_p
+	      && two_value_replacement (bb, bb1, e2, phi, arg0, arg1))
 	    cfgchanged = true;
-	  else if (match_simplify_replacement (bb, bb1, e1, e2, phi,
-					       arg0, arg1,
-					       early_p))
+	  else if (!diamond_minmax_p
+		   && match_simplify_replacement (bb, bb1, e1, e2, phi,
+						  arg0, arg1, early_p))
 	    cfgchanged = true;
 	  else if (!early_p
+		   && !diamond_minmax_p
 		   && single_pred_p (bb1)
 		   && cond_removal_in_builtin_zero_pattern (bb, bb1, e1, e2,
 							    phi, arg0, arg1))
 	    cfgchanged = true;
-	  else if (minmax_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
+	  else if (minmax_replacement (bb, bb1, bb2, e1, e2, phi, arg0, arg1,
+				       diamond_minmax_p))
 	    cfgchanged = true;
 	  else if (single_pred_p (bb1)
+		   && !diamond_minmax_p
 		   && spaceship_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
 	    cfgchanged = true;
 	}
@@ -385,7 +422,7 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads, bool early_p)
 
 static void
 replace_phi_edge_with_variable (basic_block cond_block,
-				edge e, gphi *phi, tree new_tree)
+				edge e, gphi *phi, tree new_tree, bool delete_bb = true)
 {
   basic_block bb = gimple_bb (phi);
   gimple_stmt_iterator gsi;
@@ -428,7 +465,7 @@ replace_phi_edge_with_variable (basic_block cond_block,
     edge_to_remove = EDGE_SUCC (cond_block, 1);
   else
     edge_to_remove = EDGE_SUCC (cond_block, 0);
-  if (EDGE_COUNT (edge_to_remove->dest->preds) == 1)
+  if (EDGE_COUNT (edge_to_remove->dest->preds) == 1 && delete_bb)
     {
       e->flags |= EDGE_FALLTHRU;
       e->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
@@ -1564,15 +1601,52 @@ value_replacement (basic_block cond_bb, basic_block middle_bb,
   return 0;
 }
 
+/* If VAR is an SSA_NAME that points to a BIT_NOT_EXPR then return the TREE for
+   the value being inverted.  */
+
+static tree
+strip_bit_not (tree var)
+{
+  if (TREE_CODE (var) != SSA_NAME)
+    return NULL_TREE;
+
+  gimple *assign = SSA_NAME_DEF_STMT (var);
+  if (gimple_code (assign) != GIMPLE_ASSIGN)
+    return NULL_TREE;
+
+  if (gimple_assign_rhs_code (assign) != BIT_NOT_EXPR)
+    return NULL_TREE;
+
+  return gimple_assign_rhs1 (assign);
+}
+
+/* Invert a MIN to a MAX or a MAX to a MIN expression CODE.  */
+
+enum tree_code
+invert_minmax_code (enum tree_code code)
+{
+  switch (code) {
+  case MIN_EXPR:
+    return MAX_EXPR;
+  case MAX_EXPR:
+    return MIN_EXPR;
+  default:
+    gcc_unreachable ();
+  }
+}
+
 /*  The function minmax_replacement does the main work of doing the minmax
     replacement.  Return true if the replacement is done.  Otherwise return
     false.
     BB is the basic block where the replacement is going to be done on.  ARG0
-    is argument 0 from the PHI.  Likewise for ARG1.  */
+    is argument 0 from the PHI.  Likewise for ARG1.
+
+    If THREEWAY_P then expect the BB to be laid out in diamond shape with each
+    BB containing only a MIN or MAX expression.  */
 
 static bool
-minmax_replacement (basic_block cond_bb, basic_block middle_bb,
-		    edge e0, edge e1, gphi *phi, tree arg0, tree arg1)
+minmax_replacement (basic_block cond_bb, basic_block middle_bb, basic_block alt_middle_bb,
+		    edge e0, edge e1, gphi *phi, tree arg0, tree arg1, bool threeway_p)
 {
   tree result;
   edge true_edge, false_edge;
@@ -1727,9 +1801,14 @@ minmax_replacement (basic_block cond_bb, basic_block middle_bb,
   if (false_edge->dest == middle_bb)
     false_edge = EDGE_SUCC (false_edge->dest, 0);
 
+  /* When THREEWAY_P then e1 will point to the edge of the final transition
+     from middle-bb to end.  */
   if (true_edge == e0)
     {
-      gcc_assert (false_edge == e1);
+      if (threeway_p)
+	gcc_assert (false_edge == EDGE_PRED (e1->src, 0));
+      else
+	gcc_assert (false_edge == e1);
       arg_true = arg0;
       arg_false = arg1;
     }
@@ -1768,6 +1847,133 @@ minmax_replacement (basic_block cond_bb, basic_block middle_bb,
       else
 	return false;
     }
+  else if (middle_bb != alt_middle_bb && threeway_p)
+    {
+      /* Recognize the following case:
+
+	 if (smaller < larger)
+	   a = MIN (smaller, c);
+	 else
+	   b = MIN (larger, c);
+	 x = PHI <a, b>
+
+	 This is equivalent to
+
+	 a = MIN (smaller, c);
+	 x = MIN (larger, a);  */
+
+      gimple *assign = last_and_only_stmt (middle_bb);
+      tree lhs, op0, op1, bound;
+      tree alt_lhs, alt_op0, alt_op1;
+      bool invert = false;
+
+      if (!single_pred_p (middle_bb)
+	  || !single_pred_p (alt_middle_bb))
+	return false;
+
+      if (!assign
+	  || gimple_code (assign) != GIMPLE_ASSIGN)
+	return false;
+
+      lhs = gimple_assign_lhs (assign);
+      ass_code = gimple_assign_rhs_code (assign);
+      if (ass_code != MAX_EXPR && ass_code != MIN_EXPR)
+	return false;
+
+      op0 = gimple_assign_rhs1 (assign);
+      op1 = gimple_assign_rhs2 (assign);
+
+      assign = last_and_only_stmt (alt_middle_bb);
+      if (!assign
+	  || gimple_code (assign) != GIMPLE_ASSIGN)
+	return false;
+
+      alt_lhs = gimple_assign_lhs (assign);
+      if (ass_code != gimple_assign_rhs_code (assign))
+	return false;
+
+      alt_op0 = gimple_assign_rhs1 (assign);
+      alt_op1 = gimple_assign_rhs2 (assign);
+
+      if (!operand_equal_for_phi_arg_p (lhs, arg_true)
+	 || !operand_equal_for_phi_arg_p (alt_lhs, arg_false))
+	return false;
+
+      if ((operand_equal_for_phi_arg_p (op0, smaller)
+		|| (alt_smaller
+		    && operand_equal_for_phi_arg_p (op0, alt_smaller)))
+	       && (operand_equal_for_phi_arg_p (alt_op0, larger)
+		   || (alt_larger
+		       && operand_equal_for_phi_arg_p (alt_op0, alt_larger))))
+	{
+	  /* We got here if the condition is true, i.e., SMALLER < LARGER.  */
+	  if (!operand_equal_for_phi_arg_p (op1, alt_op1))
+	    return false;
+
+	  if ((arg0 = strip_bit_not (op0)) != NULL
+	      && (arg1 = strip_bit_not (alt_op0)) != NULL
+	      && (bound = strip_bit_not (op1)) != NULL)
+	    {
+	      minmax = MAX_EXPR;
+	      ass_code = invert_minmax_code (ass_code);
+	      invert = true;
+	    }
+	  else
+	    {
+	      bound = op1;
+	      minmax = MIN_EXPR;
+	      arg0 = op0;
+	      arg1 = alt_op0;
+	     }
+	}
+      else if ((operand_equal_for_phi_arg_p (op0, larger)
+		|| (alt_larger
+		    && operand_equal_for_phi_arg_p (op0, alt_larger)))
+	       && (operand_equal_for_phi_arg_p (alt_op0, smaller)
+		   || (alt_smaller
+		       && operand_equal_for_phi_arg_p (alt_op0, alt_smaller))))
+	{
+	  /* We got here if the condition is true, i.e., SMALLER > LARGER.  */
+	  if (!operand_equal_for_phi_arg_p (op1, alt_op1))
+	    return false;
+
+	  if ((arg0 = strip_bit_not (op0)) != NULL
+	      && (arg1 = strip_bit_not (alt_op0)) != NULL
+	      && (bound = strip_bit_not (op1)) != NULL)
+	    {
+	      minmax = MIN_EXPR;
+	      ass_code = invert_minmax_code (ass_code);
+	      invert = true;
+	    }
+	  else
+	    {
+	      bound = op1;
+	      minmax = MAX_EXPR;
+	      arg0 = op0;
+	      arg1 = alt_op0;
+	     }
+	}
+      else
+	return false;
+
+      /* Reset any range information from the basic block.  */
+      reset_flow_sensitive_info_in_bb (cond_bb);
+
+      /* Emit the statement to compute min/max.  */
+      gimple_seq stmts = NULL;
+      tree phi_result = PHI_RESULT (phi);
+      result = gimple_build (&stmts, minmax, TREE_TYPE (phi_result), arg0, bound);
+      result = gimple_build (&stmts, ass_code, TREE_TYPE (phi_result), result, arg1);
+      if (invert)
+	result = gimple_build (&stmts, BIT_NOT_EXPR, TREE_TYPE (phi_result), result);
+
+      gsi = gsi_last_bb (cond_bb);
+      gsi_insert_seq_before (&gsi, stmts, GSI_NEW_STMT);
+
+      replace_phi_edge_with_variable (cond_bb, e1, phi, result, false);
+
+      return true;
+    }
   else
     {
       /* Recognize the following case, assuming d <= u:




--