MATCH: Factor out code that for min max detection with constants

This factors out some of the code from the min/max detection
from match.pd into a function so it can be reused in other
places. This is mainly used to detect the conversions
of >= to > which causes the integer values to be changed by
one.

Changes since v1:
* factor out the checks for INTEGER_CSTs so it is more obvious.

OK? Bootstrapped and tested on x86_64-linux-gnu.

gcc/ChangeLog:

	* match.pd: Factor out the deciding the min/max from
	the "(cond (cmp (convert1? x) c1) (convert2? x) c2)"
	pattern to ...
	* fold-const.cc (minmax_from_comparison): this new function.
	* fold-const.h (minmax_from_comparison): New prototype.

1 files changed, 44 insertions, 0 deletions

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 3b397ae..7d2352d 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -150,6 +150,50 @@ static tree fold_convert_const (enum tree_code, tree, tree);
 static tree fold_view_convert_expr (tree, tree);
 static tree fold_negate_expr (location_t, tree);
 
+/* This is a helper function to detect min/max for some operands of COND_EXPR.
+   The form is "(EXP0 CMP EXP1) ? EXP2 : EXP3". */
+tree_code
+minmax_from_comparison (tree_code cmp, tree exp0, tree exp1, tree exp2, tree exp3)
+{
+  enum tree_code code = ERROR_MARK;
+
+  if (HONOR_NANS (exp0) || HONOR_SIGNED_ZEROS (exp0))
+    return ERROR_MARK;
+
+  if (!operand_equal_p (exp0, exp2))
+    return ERROR_MARK;
+
+  if (TREE_CODE (exp3) == INTEGER_CST && TREE_CODE (exp1) == INTEGER_CST)
+    {
+      if (wi::to_widest (exp1) == (wi::to_widest (exp3) - 1))
+	{
+	  /* X <= Y - 1 equals to X < Y.  */
+	  if (cmp == LE_EXPR)
+	    code = LT_EXPR;
+	  /* X > Y - 1 equals to X >= Y.  */
+	  if (cmp == GT_EXPR)
+	    code = GE_EXPR;
+	}
+      if (wi::to_widest (exp1) == (wi::to_widest (exp3) + 1))
+	{
+	  /* X < Y + 1 equals to X <= Y.  */
+	  if (cmp == LT_EXPR)
+	    code = LE_EXPR;
+	  /* X >= Y + 1 equals to X > Y.  */
+	  if (cmp == GE_EXPR)
+	  code = GT_EXPR;
+	}
+    }
+  if (code != ERROR_MARK
+      || operand_equal_p (exp1, exp3))
+    {
+      if (cmp == LT_EXPR || cmp == LE_EXPR)
+	code = MIN_EXPR;
+      if (cmp == GT_EXPR || cmp == GE_EXPR)
+	code = MAX_EXPR;
+    }
+  return code;
+}
 
 /* Return EXPR_LOCATION of T if it is not UNKNOWN_LOCATION.
    Otherwise, return LOC.  */