phiopt: Optimize x < 0 ? ~y : y to (x >> 31) ^ y [PR96928]

As requested in the PR, the one's complement abs can be done more
efficiently without cmov or branching.

Had to change the ifcvt-onecmpl-abs-1.c testcase, we no longer optimize
it in ifcvt, on x86_64 with -m32 we generate in the end the exact same
code, but with -m64:
        movl    %edi, %eax
-       notl    %eax
-       cmpl    %edi, %eax
-       cmovl   %edi, %eax
+       sarl    $31, %eax
+       xorl    %edi, %eax
        ret

2021-01-05  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/96928
	* tree-ssa-phiopt.c (xor_replacement): New function.
	(tree_ssa_phiopt_worker): Call it.

	* gcc.dg/tree-ssa/pr96928.c: New test.
	* gcc.target/i386/ifcvt-onecmpl-abs-1.c: Remove -fdump-rtl-ce1,
	instead of scanning rtl dump for ifcvt message check assembly
	for xor instruction.

3 files changed, 148 insertions, 2 deletions

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr96928.c b/gcc/testsuite/gcc.dg/tree-ssa/pr96928.c
new file mode 100644
index 0000000..2091357
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr96928.c
@@ -0,0 +1,38 @@
+/* PR tree-optimization/96928 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-phiopt2" } */
+/* { dg-final { scan-tree-dump-times " = a_\[0-9]*\\\(D\\\) >> " 5 "phiopt2" } } */
+/* { dg-final { scan-tree-dump-times " = ~c_\[0-9]*\\\(D\\\);" 1 "phiopt2" } } */
+/* { dg-final { scan-tree-dump-times " = ~" 1 "phiopt2" } } */
+/* { dg-final { scan-tree-dump-times " = \[abc_0-9\\\(\\\)D]* \\\^ " 5 "phiopt2" } } */
+/* { dg-final { scan-tree-dump-not "a < 0" "phiopt2" } } */
+
+int
+foo (int a)
+{
+  return a < 0 ? ~a : a;
+}
+
+int
+bar (int a, int b)
+{
+  return a < 0 ? ~b : b;
+}
+
+unsigned
+baz (int a, unsigned int b)
+{
+  return a < 0 ? ~b : b;
+}
+
+unsigned
+qux (int a, unsigned int c)
+{
+  return a >= 0 ? ~c : c;
+}
+
+int
+corge (int a, int b)
+{
+  return a >= 0 ? b : ~b;
+}
diff --git a/gcc/testsuite/gcc.target/i386/ifcvt-onecmpl-abs-1.c b/gcc/testsuite/gcc.target/i386/ifcvt-onecmpl-abs-1.c
index 195da3f..6e02dd7 100644
--- a/gcc/testsuite/gcc.target/i386/ifcvt-onecmpl-abs-1.c
+++ b/gcc/testsuite/gcc.target/i386/ifcvt-onecmpl-abs-1.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-rtl-ce1" } */
+/* { dg-options "-O2" } */
 
 /* Check code generation for one's complement version of abs */
 
@@ -10,4 +10,4 @@ int onecmplabs(int x)
   return x;
 }
 
-/* { dg-final { scan-rtl-dump "succeeded through noce_try_abs" "ce1" } } */
+/* { dg-final { scan-assembler "\txor" } } */
diff --git a/gcc/tree-ssa-phiopt.c b/gcc/tree-ssa-phiopt.c
index 7ab2888..bbc78af 100644
--- a/gcc/tree-ssa-phiopt.c
+++ b/gcc/tree-ssa-phiopt.c
@@ -62,6 +62,8 @@ static bool minmax_replacement (basic_block, basic_block,
 				edge, edge, gimple *, tree, tree);
 static bool abs_replacement (basic_block, basic_block,
 			     edge, edge, gimple *, tree, tree);
+static bool xor_replacement (basic_block, basic_block,
+			     edge, edge, gimple *, tree, tree);
 static bool cond_removal_in_popcount_clz_ctz_pattern (basic_block, basic_block,
 						      edge, edge, gimple *,
 						      tree, tree);
@@ -346,6 +348,9 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads, bool early_p)
 	  else if (abs_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
 	    cfgchanged = true;
 	  else if (!early_p
+		   && xor_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
+	    cfgchanged = true;
+	  else if (!early_p
 		   && cond_removal_in_popcount_clz_ctz_pattern (bb, bb1, e1,
 								e2, phi, arg0,
 								arg1))
@@ -2098,6 +2103,109 @@ abs_replacement (basic_block cond_bb, basic_block middle_bb,
   return true;
 }
 
+/* Optimize x < 0 ? ~y : y into (x >> (prec-1)) ^ y.  */
+
+static bool
+xor_replacement (basic_block cond_bb, basic_block middle_bb,
+		 edge e0 ATTRIBUTE_UNUSED, edge e1,
+		 gimple *phi, tree arg0, tree arg1)
+{
+  if (!INTEGRAL_TYPE_P (TREE_TYPE (arg1)))
+    return false;
+
+  /* OTHER_BLOCK must have only one executable statement which must have the
+     form arg0 = ~arg1 or arg1 = ~arg0.  */
+
+  gimple *assign = last_and_only_stmt (middle_bb);
+  /* If we did not find the proper one's complement assignment, then we cannot
+     optimize.  */
+  if (assign == NULL)
+    return false;
+
+  /* If we got here, then we have found the only executable statement
+     in OTHER_BLOCK.  If it is anything other than arg = ~arg1 or
+     arg1 = ~arg0, then we cannot optimize.  */
+  if (!is_gimple_assign (assign))
+    return false;
+
+  if (gimple_assign_rhs_code (assign) != BIT_NOT_EXPR)
+    return false;
+
+  tree lhs = gimple_assign_lhs (assign);
+  tree rhs = gimple_assign_rhs1 (assign);
+
+  /* The assignment has to be arg0 = -arg1 or arg1 = -arg0.  */
+  if (!(lhs == arg0 && rhs == arg1) && !(lhs == arg1 && rhs == arg0))
+    return false;
+
+  gimple *cond = last_stmt (cond_bb);
+  tree result = PHI_RESULT (phi);
+
+  /* Only relationals comparing arg[01] against zero are interesting.  */
+  enum tree_code cond_code = gimple_cond_code (cond);
+  if (cond_code != LT_EXPR && cond_code != GE_EXPR)
+    return false;
+
+  /* Make sure the conditional is x OP 0.  */
+  tree clhs = gimple_cond_lhs (cond);
+  if (TREE_CODE (clhs) != SSA_NAME
+      || !INTEGRAL_TYPE_P (TREE_TYPE (clhs))
+      || TYPE_UNSIGNED (TREE_TYPE (clhs))
+      || TYPE_PRECISION (TREE_TYPE (clhs)) != TYPE_PRECISION (TREE_TYPE (arg1))
+      || !integer_zerop (gimple_cond_rhs (cond)))
+    return false;
+
+  /* We need to know which is the true edge and which is the false
+     edge so that we know if have xor or inverted xor.  */
+  edge true_edge, false_edge;
+  extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);
+
+  /* For GE_EXPR, if the true edge goes to OTHER_BLOCK, then we
+     will need to invert the result.  Similarly for LT_EXPR if
+     the false edge goes to OTHER_BLOCK.  */
+  edge e;
+  if (cond_code == GE_EXPR)
+    e = true_edge;
+  else
+    e = false_edge;
+
+  bool invert = e->dest == middle_bb;
+
+  result = duplicate_ssa_name (result, NULL);
+
+  gimple_stmt_iterator gsi = gsi_last_bb (cond_bb);
+
+  int prec = TYPE_PRECISION (TREE_TYPE (clhs));
+  gimple *new_stmt
+    = gimple_build_assign (make_ssa_name (TREE_TYPE (clhs)), RSHIFT_EXPR, clhs,
+			   build_int_cst (integer_type_node, prec - 1));
+  gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
+
+  if (!useless_type_conversion_p (TREE_TYPE (result), TREE_TYPE (clhs)))
+    {
+      new_stmt = gimple_build_assign (make_ssa_name (TREE_TYPE (result)),
+				      NOP_EXPR, gimple_assign_lhs (new_stmt));
+      gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
+    }
+  lhs = gimple_assign_lhs (new_stmt);
+
+  if (invert)
+    {
+      new_stmt = gimple_build_assign (make_ssa_name (TREE_TYPE (result)),
+				      BIT_NOT_EXPR, rhs);
+      gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
+      rhs = gimple_assign_lhs (new_stmt);
+    }
+
+  new_stmt = gimple_build_assign (result, BIT_XOR_EXPR, lhs, rhs);
+  gsi_insert_before (&gsi, new_stmt, GSI_NEW_STMT);
+
+  replace_phi_edge_with_variable (cond_bb, e1, phi, result);
+
+  /* Note that we optimized this PHI.  */
+  return true;
+}
+
 /* Auxiliary functions to determine the set of memory accesses which
    can't trap because they are preceded by accesses to the same memory
    portion.  We do that for MEM_REFs, so we only need to track