[gcc r11-5702] tree-ssa-threadedge.c (record_temporary_equivalences_from_stmts_at_dest): Do not allow __builtin_con

[Ilya Leoshkevich <iii@gcc.gnu.org>]

https://gcc.gnu.org/g:614aff0adf8fba5d843ec894603160151c20f0aa

commit r11-5702-g614aff0adf8fba5d843ec894603160151c20f0aa
Author: Ilya Leoshkevich <iii@linux.ibm.com>
Date:   Thu Dec 3 01:38:47 2020 +0100

    tree-ssa-threadedge.c (record_temporary_equivalences_from_stmts_at_dest): Do not allow __builtin_constant_p.
    
    This is the same as commit 70a62009181f ("tree-ssa-threadbackward.c
    (profitable_jump_thread_path): Do not allow __builtin_constant_p."), but
    for the old forward threader.
    
    gcc/ChangeLog:
    
    2020-12-03  Ilya Leoshkevich  <iii@linux.ibm.com>
    
            * tree-ssa-threadedge.c (record_temporary_equivalences_from_stmts_at_dest):
            Do not allow __builtin_constant_p on a threading path.

Diff:
---
 gcc/tree-ssa-threadedge.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c
index f43d5812270..32d63a95af4 100644
--- a/gcc/tree-ssa-threadedge.c
+++ b/gcc/tree-ssa-threadedge.c
@@ -265,6 +265,12 @@ record_temporary_equivalences_from_stmts_at_dest (edge e,
 	  && gimple_call_internal_unique_p (stmt))
 	return NULL;
 
+      /* We cannot thread through __builtin_constant_p, because an
+	 expression that is constant on two threading paths may become
+	 non-constant (i.e.: phi) when they merge.  */
+      if (gimple_call_builtin_p (stmt, BUILT_IN_CONSTANT_P))
+	return NULL;
+
       /* If duplicating this block is going to cause too much code
 	 expansion, then do not thread through this block.  */
       stmt_count++;