[PATCH] RISC-V: Add LCM delete block predecessors dump information

[Juzhe-Zhong]

While looking into PR113469, I notice the LCM delete a vsetvl incorrectly.

This patch add dump information of all predecessors for LCM delete vsetvl block
for better debugging.

Tested no regression.

gcc/ChangeLog:

        * config/riscv/riscv-vsetvl.cc (get_all_predecessors): New function.
        (pre_vsetvl::pre_global_vsetvl_info): Add LCM delete block all 
predecessors dump information.

---
 gcc/config/riscv/riscv-vsetvl.cc | 42 ++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/gcc/config/riscv/riscv-vsetvl.cc b/gcc/config/riscv/riscv-vsetvl.cc
index 72c5a127d9e..da258b964fc 100644
--- a/gcc/config/riscv/riscv-vsetvl.cc
+++ b/gcc/config/riscv/riscv-vsetvl.cc
@@ -654,6 +654,31 @@ invalid_opt_bb_p (basic_block cfg_bb)
   return false;
 }
 
+/* Get all predecessors of BB.  */
+static hash_set<basic_block>
+get_all_predecessors (basic_block bb)
+{
+  hash_set<basic_block> blocks;
+  auto_vec<basic_block> work_list;
+  hash_set<basic_block> visited_list;
+  work_list.safe_push (bb);
+
+  while (!work_list.is_empty ())
+    {
+      basic_block new_bb = work_list.pop ();
+      visited_list.add (new_bb);
+      edge e;
+      edge_iterator ei;
+      FOR_EACH_EDGE (e, ei, new_bb->preds)
+       {
+         if (!visited_list.contains (e->src))
+           work_list.safe_push (e->src);
+         blocks.add (e->src);
+       }
+    }
+  return blocks;
+}
+
 /* This flags indicates the minimum demand of the vl and vtype values by the
    RVV instruction. For example, DEMAND_RATIO_P indicates that this RVV
    instruction only needs the SEW/LMUL ratio to remain the same, and does not
@@ -3142,6 +3167,23 @@ pre_vsetvl::pre_global_vsetvl_info ()
       const vsetvl_block_info &block_info = get_block_info (info.get_bb ());
       gcc_assert (block_info.get_entry_info () == info);
       info.set_delete ();
+      if (dump_file && (dump_flags & TDF_DETAILS))
+       {
+         fprintf (dump_file,
+                  "\nLCM deleting vsetvl of block %d, it has predecessors: \n",
+                  bb->index ());
+         hash_set<basic_block> all_preds
+           = get_all_predecessors (bb->cfg_bb ());
+         int i = 0;
+         for (const auto pred : all_preds)
+           {
+             fprintf (dump_file, "%d ", pred->index);
+             i++;
+             if (i % 32 == 0)
+               fprintf (dump_file, "\n");
+           }
+         fprintf (dump_file, "\n");
+       }
     }
 
   /* Remove vsetvl infos if all precessors are available to the block.  */
-- 
2.36.3