[PATCH] teach phi-opt to produce -(a COND b)

[Paolo Bonzini]

This patch teaches phiopt to look at phis whose arguments are -1 and 0,
and produce negated setcc statements.

Bootstrapped/regtested x86_64-pc-linux-gnu, together with the patch
for pr53138.  Ok for mainline?

Paolo

2012-04-27  Paolo Bonzini  <bonzini@gnu.org>

        * tree-ssa-phiopt.c (conditional_replacement): Replace PHIs
	whose arguments are -1 and 0, by negating the result of the
	conditional.

2012-04-27  Paolo Bonzini  <bonzini@gnu.org>

        * gcc.c-torture/execute/20120427-2.c: New testcase.
        * gcc.dg/tree-ssa/phi-opt-10.c: New testcase.


Index: tree-ssa-phiopt.c
===================================================================
--- tree-ssa-phiopt.c	(revisione 186859)
+++ tree-ssa-phiopt.c	(copia locale)
@@ -536,17 +536,21 @@
   gimple_stmt_iterator gsi;
   edge true_edge, false_edge;
   tree new_var, new_var2;
+  bool neg;
 
   /* FIXME: Gimplification of complex type is too hard for now.  */
   if (TREE_CODE (TREE_TYPE (arg0)) == COMPLEX_TYPE
       || TREE_CODE (TREE_TYPE (arg1)) == COMPLEX_TYPE)
     return false;
 
-  /* The PHI arguments have the constants 0 and 1, then convert
-     it to the conditional.  */
+  /* The PHI arguments have the constants 0 and 1, or 0 and -1, then
+     convert it to the conditional.  */
   if ((integer_zerop (arg0) && integer_onep (arg1))
       || (integer_zerop (arg1) && integer_onep (arg0)))
-    ;
+    neg = false;
+  else if ((integer_zerop (arg0) && integer_all_onesp (arg1))
+	   || (integer_zerop (arg1) && integer_all_onesp (arg0)))
+    neg = true;
   else
     return false;
 
@@ -558,7 +562,7 @@
      falls through into BB.
 
      There is a single PHI node at the join point (BB) and its arguments
-     are constants (0, 1).
+     are constants (0, 1) or (0, -1).
 
      So, given the condition COND, and the two PHI arguments, we can
      rewrite this PHI into non-branching code:
@@ -585,12 +589,20 @@
      edge so that we know when to invert the condition below.  */
   extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);
   if ((e0 == true_edge && integer_zerop (arg0))
-      || (e0 == false_edge && integer_onep (arg0))
+      || (e0 == false_edge && !integer_zerop (arg0))
       || (e1 == true_edge && integer_zerop (arg1))
-      || (e1 == false_edge && integer_onep (arg1)))
+      || (e1 == false_edge && !integer_zerop (arg1)))
     cond = fold_build1_loc (gimple_location (stmt),
-			    TRUTH_NOT_EXPR, TREE_TYPE (cond), cond);
+                            TRUTH_NOT_EXPR, TREE_TYPE (cond), cond);
 
+  if (neg)
+    {
+      cond = fold_convert_loc (gimple_location (stmt),
+                               TREE_TYPE (result), cond);
+      cond = fold_build1_loc (gimple_location (stmt),
+                              NEGATE_EXPR, TREE_TYPE (cond), cond);
+    }
+
   /* Insert our new statements at the end of conditional block before the
      COND_STMT.  */
   gsi = gsi_for_stmt (stmt);
Index: testsuite/gcc.c-torture/execute/20120427-2.c
===================================================================
--- testsuite/gcc.c-torture/execute/20120427-2.c	(revisione 0)
+++ testsuite/gcc.c-torture/execute/20120427-2.c	(revisione 0)
@@ -0,0 +1,38 @@
+typedef struct sreal
+{
+  unsigned sig;		/* Significant.  */
+  int exp;		/* Exponent.  */
+} sreal;
+
+sreal_compare (sreal *a, sreal *b)
+{
+  if (a->exp > b->exp)
+    return 1;
+  if (a->exp < b->exp)
+    return -1;
+  if (a->sig > b->sig)
+    return 1;
+  if (a->sig < b->sig)
+    return -1;
+  return 0;
+}
+
+sreal a[] = {
+   { 0, 0 },
+   { 1, 0 },
+   { 0, 1 },
+   { 1, 1 }
+};
+
+int main()
+{
+  int i, j;
+  for (i = 0; i <= 3; i++) {
+    for (j = 0; j < 3; j++) {
+      if (i < j && sreal_compare(&a[i], &a[j]) != -1) abort();
+      if (i == j && sreal_compare(&a[i], &a[j]) != 0) abort();
+      if (i > j && sreal_compare(&a[i], &a[j]) != 1) abort();
+    }
+  }
+  return 0;
+}
Index: testsuite/gcc.dg/tree-ssa/phi-opt-10.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/phi-opt-10.c	(revisione 0)
+++ testsuite/gcc.dg/tree-ssa/phi-opt-10.c	(revisione 0)
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdump-tree-optimized" } */
+
+int nem1_phi (unsigned long a) { return a ? -1 : 0; }
+int eqm1_phi (unsigned long a) { return a ? 0 : -1; }
+
+int spaceship1 (long a) { return a > 0 ? 1 : a < 0 ? -1 : 0; }
+int spaceship2 (long a) { return a > 0 ? 1 : a == 0 ? 0 : -1; }
+
+/* { dg-final { scan-tree-dump-times " = -D" 4 "optimized"} } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */