[tree-optimization] : Improve handling of conditional-branches on targets with high branch costs

Hello,

So I committed the gimplify patch separate.  And here is the remaining
fold-const patch.
The important tests here are in gcc.dg/tree-ssa/builtin-expect[1-4].c, which
cover the one special-case for branching. Also tree-ssa/20040204-1.c covers
tests for branching code (on targets having high-engough BRANCH_COST and no
special-casing - like MIPS, S/390, and AVR.

ChangeLog

2011-10-14  Kai Tietz  <ktietz@redhat.com>

	* fold-const.c (simple_operand_p_2): New function.
	(fold_truthop): Rename to
	(fold_truth_andor_1): function name.
	Additionally remove branching creation for logical and/or.
	(fold_truth_andor): Handle branching creation for logical and/or here.

Bootstrapped and regression-tested for all languages plus Ada and
Obj-C++ on x86_64-pc-linux-gnu.
Ok for apply?

Regards,
Kai

 static tree extract_muldiv (tree, tree, enum tree_code, tree, bool *);
@@ -3500,7 +3500,7 @@ optimize_bit_field_compare (location_t l
   return lhs;
 }
 
-/* Subroutine for fold_truthop: decode a field reference.
+/* Subroutine for fold_truth_andor_1: decode a field reference.

    If EXP is a comparison reference, we return the innermost reference.

@@ -3668,7 +3668,7 @@ sign_bit_p (tree exp, const_tree val)
   return NULL_TREE;
 }

-/* Subroutine for fold_truthop: determine if an operand is simple enough
+/* Subroutine for fold_truth_andor_1: determine if an operand is simple enough
    to be evaluated unconditionally.  */

 static int
@@ -3678,7 +3678,7 @@ simple_operand_p (const_tree exp)
   STRIP_NOPS (exp);

   return (CONSTANT_CLASS_P (exp)
-	  || TREE_CODE (exp) == SSA_NAME
+  	  || TREE_CODE (exp) == SSA_NAME
 	  || (DECL_P (exp)
 	      && ! TREE_ADDRESSABLE (exp)
 	      && ! TREE_THIS_VOLATILE (exp)
@@ -3692,6 +3692,46 @@ simple_operand_p (const_tree exp)
 		 registers aren't expensive.  */
 	      && (! TREE_STATIC (exp) || DECL_REGISTER (exp))));
 }
+
+/* Subroutine for fold_truth_andor: determine if an operand is simple enough
+   to be evaluated unconditionally.
+   I addition to simple_operand_p, we assume that comparisons and logic-not
+   operations are simple, if their operands are simple, too.  */
+
+static bool
+simple_operand_p_2 (tree exp)
+{
+  enum tree_code code;
+
+  /* Strip any conversions that don't change the machine mode.  */
+  STRIP_NOPS (exp);
+
+  code = TREE_CODE (exp);
+
+  if (TREE_CODE_CLASS (code) == tcc_comparison)
+    return (!tree_could_trap_p (exp)
+	    && simple_operand_p_2 (TREE_OPERAND (exp, 0))
+	    && simple_operand_p_2 (TREE_OPERAND (exp, 1)));
+
+  if (TREE_SIDE_EFFECTS (exp)
+      || tree_could_trap_p (exp))
+    return false;
+
+  switch (code)
+    {
+    case SSA_NAME:
+      return true;
+    case TRUTH_NOT_EXPR:
+      return simple_operand_p_2 (TREE_OPERAND (exp, 0));
+    case BIT_NOT_EXPR:
+      if (TREE_CODE (TREE_TYPE (exp)) != BOOLEAN_TYPE)
+	return false;
+      return simple_operand_p_2 (TREE_OPERAND (exp, 0));
+    default:
+      return simple_operand_p (exp);
+    }
+}
+
 
 /* The following functions are subroutines to fold_range_test and allow it to
    try to change a logical combination of comparisons into a range test.
@@ -4888,7 +4928,7 @@ fold_range_test (location_t loc, enum tr
   return 0;
 }
 
-/* Subroutine for fold_truthop: C is an INTEGER_CST interpreted as a P
+/* Subroutine for fold_truth_andor_1: C is an INTEGER_CST interpreted as a P
    bit value.  Arrange things so the extra bits will be set to zero if and
    only if C is signed-extended to its full width.  If MASK is nonzero,
    it is an INTEGER_CST that should be AND'ed with the extra bits.  */
@@ -5025,8 +5065,8 @@ merge_truthop_with_opposite_arm (locatio
    We return the simplified tree or 0 if no optimization is possible.  */

 static tree
-fold_truthop (location_t loc, enum tree_code code, tree truth_type,
-	      tree lhs, tree rhs)
+fold_truth_andor_1 (location_t loc, enum tree_code code, tree truth_type,
+		    tree lhs, tree rhs)
 {
   /* If this is the "or" of two comparisons, we can do something if
      the comparisons are NE_EXPR.  If this is the "and", we can do something
@@ -5054,8 +5094,6 @@ fold_truthop (location_t loc, enum tree_
   tree lntype, rntype, result;
   HOST_WIDE_INT first_bit, end_bit;
   int volatilep;
-  tree orig_lhs = lhs, orig_rhs = rhs;
-  enum tree_code orig_code = code;

   /* Start by getting the comparison codes.  Fail if anything is volatile.
      If one operand is a BIT_AND_EXPR with the constant one, treat it as if
@@ -5119,8 +5157,7 @@ fold_truthop (location_t loc, enum tree_
   /* If the RHS can be evaluated unconditionally and its operands are
      simple, it wins to evaluate the RHS unconditionally on machines
      with expensive branches.  In this case, this isn't a comparison
-     that can be merged.  Avoid doing this if the RHS is a floating-point
-     comparison since those can trap.  */
+     that can be merged.  */

   if (BRANCH_COST (optimize_function_for_speed_p (cfun),
 		   false) >= 2
@@ -5149,13 +5186,6 @@ fold_truthop (location_t loc, enum tree_
 			   build2 (BIT_IOR_EXPR, TREE_TYPE (ll_arg),
 				   ll_arg, rl_arg),
 			   build_int_cst (TREE_TYPE (ll_arg), 0));
-
-      if (LOGICAL_OP_NON_SHORT_CIRCUIT)
-	{
-	  if (code != orig_code || lhs != orig_lhs || rhs != orig_rhs)
-	    return build2_loc (loc, code, truth_type, lhs, rhs);
-	  return NULL_TREE;
-	}
     }

   /* See if the comparisons can be merged.  Then get all the parameters for
@@ -8380,13 +8410,49 @@ fold_truth_andor (location_t loc, enum t
      lhs is another similar operation, try to merge its rhs with our
      rhs.  Then try to merge our lhs and rhs.  */
   if (TREE_CODE (arg0) == code
-      && 0 != (tem = fold_truthop (loc, code, type,
-				   TREE_OPERAND (arg0, 1), arg1)))
+      && 0 != (tem = fold_truth_andor_1 (loc, code, type,
+					 TREE_OPERAND (arg0, 1), arg1)))
     return fold_build2_loc (loc, code, type, TREE_OPERAND (arg0, 0), tem);

-  if ((tem = fold_truthop (loc, code, type, arg0, arg1)) != 0)
+  if ((tem = fold_truth_andor_1 (loc, code, type, arg0, arg1)) != 0)
     return tem;

+  if ((code == TRUTH_ANDIF_EXPR || code == TRUTH_ORIF_EXPR)
+      && (BRANCH_COST (optimize_function_for_speed_p (cfun),
+		       false) >= 2)
+      && LOGICAL_OP_NON_SHORT_CIRCUIT
+      && simple_operand_p_2 (arg1))
+    {
+      enum tree_code ncode = (code == TRUTH_ANDIF_EXPR ? TRUTH_AND_EXPR
+						       : TRUTH_OR_EXPR);
+
+      /* Transform ((A AND-IF B) AND-IF C) into (A AND-IF (B AND C)),
+         or ((A OR-IF B) OR-IF C) into (A OR-IF (B OR C))
+         We don't want to pack more than two leafs to a non-IF AND/OR
+         expression.
+         If tree-code of left-hand operand isn't an AND/OR-IF code and not
+         equal to CODE, then we don't want to add right-hand operand.
+         If the inner right-hand side of left-hand operand has side-effects,
+         or isn't simple, then we can't add to it, as otherwise we might
+         destroy if-sequence.  */
+      if (TREE_CODE (arg0) == code
+      	  /* Needed for sequence points to handle trappings, and
+      	     side-effects.  */
+      	  && simple_operand_p_2 (TREE_OPERAND (arg0, 1)))
+       {
+         tem = fold_build2_loc (loc, ncode, type, TREE_OPERAND (arg0, 1),
+				arg1);
+         return fold_build2_loc (loc, code, type, TREE_OPERAND (arg0, 0),
+				 tem);
+       }
+     /* Transform (A AND-IF B) into (A AND B), or (A OR-IF B)
+        into (A OR B).
+        For sequence point consistancy, we need to check for trapping, and
+        side-effects.  */
+     else if (simple_operand_p_2 (arg0))
+       return fold_build2_loc (loc, ncode, type, arg0, arg1);
+    }
+
   return NULL_TREE;
 }


[tree-optimization] : Improve handling of conditional-branches on targets with high branch costs

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