[gcc r17-3464] Fixup tree_nop_conversion_p WRT BLKmode vector types

https://gcc.gnu.org/g:ffb9629b258229099c8f47d391af7897a640b2cd

commit r17-3464-gffb9629b258229099c8f47d391af7897a640b2cd
Author: Richard Biener <[email protected]>
Date:   Thu Aug 13 15:23:01 2026 +0200

    Fixup tree_nop_conversion_p WRT BLKmode vector types
    
    This special-cases BLKmode vector types appropriately.
    
            * tree.cc (tree_nop_conversion_p): Special case two BLKmode
            types.

Diff:
---
 gcc/tree.cc | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/gcc/tree.cc b/gcc/tree.cc
index 19069eb59607..52313fbd129f 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -12462,6 +12462,19 @@ tree_nop_conversion_p (const_tree outer_type, const_tree inner_type)
 	  || TREE_CODE (inner_type) == OFFSET_TYPE))
     return TYPE_PRECISION (outer_type) == TYPE_PRECISION (inner_type);
 
+  if (TYPE_MODE (outer_type) == BLKmode
+      && TYPE_MODE (inner_type) == BLKmode)
+    {
+      if (VECTOR_TYPE_P (outer_type)
+	  && VECTOR_TYPE_P (inner_type)
+	  && known_eq (TYPE_VECTOR_SUBPARTS (outer_type),
+		       TYPE_VECTOR_SUBPARTS (inner_type))
+	  && (TYPE_MODE (TREE_TYPE (outer_type))
+	      == TYPE_MODE (TREE_TYPE (inner_type))))
+	return true;
+      return false;
+    }
+
   /* Otherwise fall back on comparing machine modes (e.g. for
      aggregate types, floats).  */
   return TYPE_MODE (outer_type) == TYPE_MODE (inner_type);