[PATCH] vect: Allow unsigned-to-signed promotion in vect_look_through_possible_promotion [PR115707]

[Feng Xue OS]

The function vect_look_through_possible_promotion() fails to figure out root
definition if casts involves more than two promotions with sign change as:

long a = (long)b;       // promotion cast
 -> int b = (int)c;     // promotion cast, sign change
   -> unsigned short c = ...;

For this case, the function thinks the 2nd cast has different sign as the 1st,
so stop looking through, while "unsigned short -> integer" is a nature sign
extension. This patch allows this unsigned-to-signed promotion in the function.

Thanks,
Feng

---
gcc/
        * tree-vect-patterns.cc (vect_look_through_possible_promotion): Allow
        unsigned-to-signed promotion.
---
 gcc/tree-vect-patterns.cc | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index 4674a16d15f..b2c83cfd219 100644
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -434,7 +434,9 @@ vect_look_through_possible_promotion (vec_info *vinfo, tree 
op,
             sign of the previous promotion.  */
          if (!res
              || TYPE_PRECISION (unprom->type) == orig_precision
-             || TYPE_SIGN (unprom->type) == TYPE_SIGN (op_type))
+             || TYPE_SIGN (unprom->type) == TYPE_SIGN (op_type)
+             || (TYPE_UNSIGNED (op_type)
+                 && TYPE_PRECISION (op_type) < TYPE_PRECISION (unprom->type)))
            {
              unprom->set_op (op, dt, caster);
              min_precision = TYPE_PRECISION (op_type);
-- 
2.17.1
From 334998e1d991e1d2c8e4c2234663b4d829e88e5c Mon Sep 17 00:00:00 2001
From: Feng Xue <f...@os.amperecomputing.com>
Date: Mon, 5 Aug 2024 15:23:56 +0800
Subject: [PATCH] vect: Allow unsigned-to-signed promotion in
 vect_look_through_possible_promotion [PR115707]

The function fails to figure out root definition if casts involves more than
two promotions with sign change as:

long a = (long)b;       // promotion cast
 -> int b = (int)c;     // promotion cast, sign change
   -> unsigned short c = ...;

For this case, the function thinks the 2nd cast has different sign as the 1st,
so stop looking through, while "unsigned short -> integer" is a nature sign
extension.

2024-08-05 Feng Xue <f...@os.amperecomputing.com>

gcc/
	* tree-vect-patterns.cc (vect_look_through_possible_promotion): Allow
	unsigned-to-signed promotion.
---
 gcc/tree-vect-patterns.cc | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index 4674a16d15f..b2c83cfd219 100644
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -434,7 +434,9 @@ vect_look_through_possible_promotion (vec_info *vinfo, tree op,
 	     sign of the previous promotion.  */
 	  if (!res
 	      || TYPE_PRECISION (unprom->type) == orig_precision
-	      || TYPE_SIGN (unprom->type) == TYPE_SIGN (op_type))
+	      || TYPE_SIGN (unprom->type) == TYPE_SIGN (op_type)
+	      || (TYPE_UNSIGNED (op_type)
+		  && TYPE_PRECISION (op_type) < TYPE_PRECISION (unprom->type)))
 	    {
 	      unprom->set_op (op, dt, caster);
 	      min_precision = TYPE_PRECISION (op_type);
-- 
2.17.1