Bug#26977 exception handlers never hreturn

  - In some cases, flow control optimization implemented in sp::optimize
    removes hreturn instructions, causing SQL exception handlers to:
      * never return
      * execute wrong logic
  - This patch overrides default short cut optimization on hreturn instructions
    to avoid this problem.


mysql-test/r/sp-code.result:
  Added test case
mysql-test/t/sp-code.test:
  Added test case
sql/sp_head.cc:
  Override opt_mark to get correct execution paths without jump short cut 
  optimization.
sql/sp_head.h:
  Added override sp_instr_hreturn::opt_shortcut_jump so that jump short cuts aren't
  performed on hreturn instructions operating on handlers which are set to CONTINUE
  after interruption.

1 files changed, 13 insertions, 3 deletions

diff --git a/sql/sp_head.cc b/sql/sp_head.cc
index 1ebef4f8bee..5a1faf50296 100644
--- a/sql/sp_head.cc
+++ b/sql/sp_head.cc
@@ -2982,10 +2982,20 @@ sp_instr_hreturn::print(String *str)
 uint
 sp_instr_hreturn::opt_mark(sp_head *sp, List<sp_instr> *leads)
 {
-  if (m_dest)
-    return sp_instr_jump::opt_mark(sp, leads);
-
   marked= 1;
+  
+  if (m_dest)
+  {
+    /*
+      This is an EXIT handler; next instruction step is in m_dest.
+     */
+    return m_dest;
+  }
+  
+  /*
+    This is a CONTINUE handler; next instruction step will come from
+    the handler stack and not from opt_mark.
+   */
   return UINT_MAX;
 }