[gcc r13-3809] CCP: handle division by a power of 2 as a right shift.

[gcc r13-3809] CCP: handle division by a power of 2 as a right shift.

[Aldy Hernandez]

https://gcc.gnu.org/g:215355d302d8602c7eeefb9c927a3dbb221714c8

commit r13-3809-g215355d302d8602c7eeefb9c927a3dbb221714c8
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Sun Nov 6 20:38:42 2022 +0100

    CCP: handle division by a power of 2 as a right shift.
    
    We have some code in range-ops that sets better maybe nonzero bits for
    TRUNC_DIV_EXPR by a power of 2 than CCP does, by just shifting the
    mask.  I'd like to offload this functionality into the CCP mask
    tracking code, which already does the right thing for right shifts.
    
    The testcase for this change is gcc.dg/tree-ssa/vrp123.c and
    gcc.dg/tree-ssa/pr107541.c.
    
    gcc/ChangeLog:
    
            * range-op.cc (operator_div::fold_range): Call
            update_known_bitmask.
            * tree-ssa-ccp.cc (bit_value_binop): Handle divisions by powers of
            2 as a right shift.

Diff:
---
 gcc/range-op.cc     | 18 +-----------------
 gcc/tree-ssa-ccp.cc | 12 ++++++++++++
 2 files changed, 13 insertions(+), 17 deletions(-)

diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index 846931ddcae..8ff5d5b4c78 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -1995,23 +1995,7 @@ operator_div::fold_range (irange &r, tree type,
   if (!cross_product_operator::fold_range (r, type, lh, rh, trio))
     return false;
 
-  if (lh.undefined_p ())
-    return true;
-
-  tree t;
-  if (code == TRUNC_DIV_EXPR
-      && rh.singleton_p (&t)
-      && !wi::neg_p (lh.lower_bound ()))
-    {
-      wide_int wi = wi::to_wide (t);
-      int shift = wi::exact_log2 (wi);
-      if (shift != -1)
-	{
-	  wide_int nz = lh.get_nonzero_bits ();
-	  nz = wi::rshift (nz, shift, TYPE_SIGN (type));
-	  r.set_nonzero_bits (nz);
-	}
-    }
+  update_known_bitmask (r, code, lh, rh);
   return true;
 }
 
diff --git a/gcc/tree-ssa-ccp.cc b/gcc/tree-ssa-ccp.cc
index 3a4b6bc1118..2bcd90646f6 100644
--- a/gcc/tree-ssa-ccp.cc
+++ b/gcc/tree-ssa-ccp.cc
@@ -1934,6 +1934,18 @@ bit_value_binop (enum tree_code code, signop sgn, int width,
       {
 	widest_int r1max = r1val | r1mask;
 	widest_int r2max = r2val | r2mask;
+	if (r2mask == 0 && !wi::neg_p (r1max))
+	  {
+	    widest_int shift = wi::exact_log2 (r2val);
+	    if (shift != -1)
+	      {
+		// Handle division by a power of 2 as an rshift.
+		bit_value_binop (RSHIFT_EXPR, sgn, width, val, mask,
+				 r1type_sgn, r1type_precision, r1val, r1mask,
+				 r2type_sgn, r2type_precision, shift, r2mask);
+		return;
+	      }
+	  }
 	if (sgn == UNSIGNED
 	    || (!wi::neg_p (r1max) && !wi::neg_p (r2max)))
 	  {