[PATCH] VEC_COND_EXPR: do not expand comparisons feeding it

[Martin Liška]

Hi.

The patch is about blocking of vector expansion of comparisons
that are only feeding a VEC_COND_EXPR statements.

Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
The problematic mips64 test-case looks good now.

Ready to be installed?
Thanks,
Martin

gcc/ChangeLog:

        * tree-vect-generic.c (expand_vector_comparison): Do not expand
        comparison that only feed first argument of a VEC_COND_EXPR statement.
---
 gcc/tree-vect-generic.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/gcc/tree-vect-generic.c b/gcc/tree-vect-generic.c
index a4b56195903..4606decd0f2 100644
--- a/gcc/tree-vect-generic.c
+++ b/gcc/tree-vect-generic.c
@@ -379,6 +379,30 @@ static tree
 expand_vector_comparison (gimple_stmt_iterator *gsi, tree type, tree op0,
                           tree op1, enum tree_code code)
 {
+  tree lhs = gimple_assign_lhs (gsi_stmt (*gsi));
+  use_operand_p use_p;
+  imm_use_iterator iterator;
+  bool vec_cond_expr_only = true;
+  bool has_use = false;
+
+  /* As seen in PR95830, we should not expand comparisons that are only
+     feeding a VEC_COND_EXPR statement.  */
+  FOR_EACH_IMM_USE_FAST (use_p, iterator, lhs)
+    {
+      has_use = true;
+      gassign *use = dyn_cast<gassign *> (USE_STMT (use_p));
+      if (use == NULL
+         || gimple_assign_rhs_code (use) != VEC_COND_EXPR
+         || gimple_assign_rhs1 (use) != lhs)
+       {
+         vec_cond_expr_only = false;
+         break;
+       }
+    }
+
+  if (has_use && vec_cond_expr_only)
+    return NULL_TREE;
+
   tree t;
   if (!expand_vec_cmp_expr_p (TREE_TYPE (op0), type, code)
       && !expand_vec_cond_expr_p (type, TREE_TYPE (op0), code))
--
2.27.0