[gcc r14-5813] tree-optimization/112344 - relax final value-replacement fix

[gcc r14-5813] tree-optimization/112344 - relax final value-replacement fix

[Richard Biener]

https://gcc.gnu.org/g:a7d82b45edeed99a850595eee0e59d16c4df7aff

commit r14-5813-ga7d82b45edeed99a850595eee0e59d16c4df7aff
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Nov 23 09:49:59 2023 +0100

    tree-optimization/112344 - relax final value-replacement fix
    
    The following tries to reduce the number of cases we use an unsigned
    type for the addition when we know the original signed increment was
    OK which is when the total unsigned increment computed fits the signed
    type as well.
    
    This fixes the observed testsuite fallout.
    
            PR tree-optimization/112344
            * tree-chrec.cc (chrec_apply): Only use an unsigned add
            when the overall increment doesn't fit the signed type.

Diff:
---
 gcc/tree-chrec.cc | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/gcc/tree-chrec.cc b/gcc/tree-chrec.cc
index f4ba130ba20..e2864e8d131 100644
--- a/gcc/tree-chrec.cc
+++ b/gcc/tree-chrec.cc
@@ -646,9 +646,21 @@ chrec_apply (unsigned var,
 	      res = chrec_fold_multiply (utype,
 					 chrec_convert (utype, chrecr, NULL),
 					 res);
-	      res = chrec_fold_plus (utype,
-				     chrec_convert (utype, chrecl, NULL), res);
-	      res = chrec_convert (type, res, NULL);
+	      /* When the resulting increment fits the original type
+		 do the increment in it.  */
+	      if (TREE_CODE (res) == INTEGER_CST
+		  && int_fits_type_p (res, TREE_TYPE (chrecr)))
+		{
+		  res = chrec_convert (TREE_TYPE (chrecr), res, NULL);
+		  res = chrec_fold_plus (type, chrecl, res);
+		}
+	      else
+		{
+		  res = chrec_fold_plus (utype,
+					 chrec_convert (utype, chrecl, NULL),
+					 res);
+		  res = chrec_convert (type, res, NULL);
+		}
 	    }
 	}
       else if (TREE_CODE (x) == INTEGER_CST