[PATCH v2] middle-end: [PR middle-end/116926] Allow widening optabs for vec-mode -> scalar-mode

[Victor Do Nascimento]

The recent refactoring of the dot_prod optab to convert-type exposed a
limitation in how `find_widening_optab_handler_and_mode' is currently
implemented, owing to the fact that, while the function expects the

  GET_MODE_CLASS (from_mode) == GET_MODE_CLASS (to_mode)

condition to hold, the c6x backend implements a dot product from V2HI
to SI, which triggers an ICE.

Consequently, this patch adds some logic to allow widening optabs
which accumulate vector elements to a single scalar.

Regression tested on x86_64 and aarch64 with no new regressions.
Fixes failing unit tests on c6x, as validated for the tic6x-unknown-elf
target.

Ok for master?

gcc/ChangeLog:

        PR middle-end/116926
        * optabs-query.cc (find_widening_optab_handler_and_mode): Add
        handling of vector -> scalar optab handling.
---
 gcc/optabs-query.cc | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/gcc/optabs-query.cc b/gcc/optabs-query.cc
index c3134d6a2ce..cc52bc0f5ea 100644
--- a/gcc/optabs-query.cc
+++ b/gcc/optabs-query.cc
@@ -485,6 +485,12 @@ find_widening_optab_handler_and_mode (optab op, 
machine_mode to_mode,
       if (GET_MODE_CLASS (limit_mode) == MODE_PARTIAL_INT)
        limit_mode = GET_MODE_WIDER_MODE (limit_mode).require ();
     }
+  else if (is_a <scalar_int_mode> (to_mode))
+    {
+      gcc_checking_assert (VECTOR_MODE_P (from_mode)
+                          && GET_MODE_INNER (from_mode) < to_mode);
+      limit_mode = from_mode;
+    }
   else
     gcc_checking_assert (GET_MODE_CLASS (from_mode) == GET_MODE_CLASS (to_mode)
                         && from_mode < to_mode);
-- 
2.34.1