[gcc r16-3131] tree-optimization/121488 - improve BIT_FIELD_REF lookup in VN

[Richard Biener via Gcc-cvs]

https://gcc.gnu.org/g:f2a85db9eee7d761692ca8f69ea1a20d32715bad

commit r16-3131-gf2a85db9eee7d761692ca8f69ea1a20d32715bad
Author: Richard Biener <rguent...@suse.de>
Date:   Mon Aug 11 09:42:09 2025 +0200

    tree-optimization/121488 - improve BIT_FIELD_REF lookup in VN
    
    When a BIT_FIELD_REF lookup combined with a defining load RHS results
    in a wrongly typed result, try looking up or inserting a VIEW_CONVERT_EXPR
    to the desired type.
    
            PR tree-optimization/121488
            * tree-ssa-sccvn.cc (visit_nary_op): If the BIT_FIELD_REF
            result is of wrong type, try a VIEW_CONVERT_EXPR around it.
    
            * gcc.dg/tree-ssa/ssa-fre-108.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-108.c | 30 +++++++++++++++++++++++++++++
 gcc/tree-ssa-sccvn.cc                       | 17 ++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-108.c 
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-108.c
new file mode 100644
index 000000000000..a13e9729e5f2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-108.c
@@ -0,0 +1,30 @@
+/* { dg-do compile } */
+/* { dg-options "-O -Wno-psabi -fdump-tree-fre1" } */
+
+#define vector16 __attribute__((vector_size(16)))
+#define vector32 __attribute__((vector_size(32)))
+
+union u1
+{
+  struct s1
+  {
+    vector16 int hi;
+    vector16 int low;
+  }hilow;
+  vector32 int v;
+};
+
+vector16 float f(vector16 int a, vector16 int b)
+{
+  union u1 c;
+  c.hilow.hi = a;
+  c.hilow.low = b;
+  vector32 int d0 = c.v;
+  vector32 float d = (vector32 float)d0;
+  vector16 float e = __builtin_shufflevector (d, d, 0, 1, 2, 3);
+  vector16 float f = __builtin_shufflevector (d, d, 4, 5, 6, 7);
+  return e/f;
+}
+
+/* { dg-final { scan-tree-dump-times "_\[0-9\]\+ = VIEW_CONVERT_EXPR" 2 "fre1" 
} } */
+/* { dg-final { scan-tree-dump-not "BIT_FIELD_REF" "fre1" } } */
diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index 866d49c15a10..61d794d84072 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -5660,6 +5660,23 @@ visit_nary_op (tree lhs, gassign *stmt)
                  if (result
                      && useless_type_conversion_p (type, TREE_TYPE (result)))
                    return set_ssa_val_to (lhs, result);
+                 else if (result
+                          && TYPE_SIZE (type)
+                          && TYPE_SIZE (TREE_TYPE (result))
+                          && operand_equal_p (TYPE_SIZE (type),
+                                              TYPE_SIZE (TREE_TYPE (result))))
+                   {
+                     gimple_match_op match_op (gimple_match_cond::UNCOND,
+                                               VIEW_CONVERT_EXPR,
+                                               type, result);
+                     result = vn_nary_build_or_lookup (&match_op);
+                     if (result)
+                       {
+                         bool changed = set_ssa_val_to (lhs, result);
+                         vn_nary_op_insert_stmt (stmt, result);
+                         return changed;
+                       }
+                   }
                }
            }
        }