ranger: Improve CLZ fold_range [PR115337]

cfn_ctz::fold_range includes special cases for the case where .CTZ has
two arguments and so is well defined at zero, and the second argument is
equal to prec or -1, but cfn_clz::fold_range does that only for the prec
case.  -1 is fairly common as well though, because the <stdbit.h> builtins
do use it now, so I think it is worth special casing that.
If we don't know anything about the argument, the difference for
.CLZ (arg, -1) is that previously the result was varying, now it will be
[-1, prec-1].  If we knew arg can't be zero, it used to be optimized before
as well into e.g. [0, prec-1] or similar.

2024-06-04  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/115337
	* gimple-range-op.cc (cfn_clz::fold_range): For
	m_gimple_call_internal_p handle as a special case also second argument
	of -1 next to prec.

diff --git a/gcc/gimple-range-op.cc b/gcc/gimple-range-op.cc
index aec3f39ec0e86e7fa00cea1eab602eb1db5c5f9d..1b9a84708b94e24ba4cdaa6c6b3fa1d5a5dbae16 100644 (file)
--- a/gcc/gimple-range-op.cc
+++ b/gcc/gimple-range-op.cc
@@ -941,8 +941,10 @@ cfn_clz::fold_range (irange &r, tree type, const irange &lh,
   int maxi = prec - 1;
   if (m_gimple_call_internal_p)
     {
-      // Only handle the single common value.
-      if (rh.lower_bound () == prec)
+      // Handle only the two common values.
+      if (rh.lower_bound () == -1)
+       mini = -1;
+      else if (rh.lower_bound () == prec)
        maxi = prec;
       else
        // Magic value to give up, unless we can prove arg is non-zero.
@@ -953,7 +955,7 @@ cfn_clz::fold_range (irange &r, tree type, const irange &lh,
   if (wi::gt_p (lh.lower_bound (), 0, TYPE_SIGN (lh.type ())))
     {
       maxi = prec - 1 - wi::floor_log2 (lh.lower_bound ());
-      if (mini == -2)
+      if (mini < 0)
        mini = 0;
     }
   else if (!range_includes_zero_p (lh))
@@ -969,11 +971,11 @@ cfn_clz::fold_range (irange &r, tree type, const irange &lh,
   if (max == 0)
     {
       // If CLZ_DEFINED_VALUE_AT_ZERO is 2 with VALUE of prec,
-      // return [prec, prec], otherwise ignore the range.
-      if (maxi == prec)
-       mini = prec;
+      // return [prec, prec] or [-1, -1], otherwise ignore the range.
+      if (maxi == prec || mini == -1)
+       mini = maxi;
     }
-  else
+  else if (mini >= 0)
     mini = newmini;
 
   if (mini == -2)