From: Jakub Jelinek <jakub@redhat.com>
Date: Thu, 16 Jan 2025 08:25:16 +0000 (+0100)
Subject: tree-ssa-propagate: Special case lhs of musttail calls in may_propagate_copy [PR118430]
X-Git-Tag: basepoints/gcc-16~2609
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=7f5adfd31b3af08924faec36679eaea40a98af19;p=thirdparty%2Fgcc.git

tree-ssa-propagate: Special case lhs of musttail calls in may_propagate_copy [PR118430]

This patch ensures that VRP or similar passes don't replace the uses of lhs of
[[gnu::musttail]] calls with some constant (e.g. if the call is known is known
to return a singleton value range) etc. to make it more likely that it is actually
tail callable.

2025-01-16  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/118430
	* tree-ssa-propagate.cc (may_propagate_copy): Return false if dest
	is lhs of an [[gnu::musttail]] call.
	(substitute_and_fold_dom_walker::before_dom_children): Formatting fix.

	* c-c++-common/musttail14.c: Expect lhs on the must tail call calls.
---

diff --git a/gcc/testsuite/c-c++-common/musttail14.c b/gcc/testsuite/c-c++-common/musttail14.c
index e2ab20bc5a4..e95bc9bc768 100644
--- a/gcc/testsuite/c-c++-common/musttail14.c
+++ b/gcc/testsuite/c-c++-common/musttail14.c
@@ -1,9 +1,9 @@
 /* PR tree-optimization/118430 */
 /* { dg-do compile { target musttail } } */
 /* { dg-options "-O2 -fdump-tree-optimized" } */
-/* { dg-final { scan-tree-dump-times "  bar \\\(\[^\n\r]\*\\\); \\\[tail call\\\] \\\[must tail call\\\]" 1 "optimized" } } */
-/* { dg-final { scan-tree-dump-times "  freddy \\\(\[^\n\r]\*\\\); \\\[tail call\\\] \\\[must tail call\\\]" 1 "optimized" } } */
-/* { dg-final { scan-tree-dump-times "  (?:bar|freddy) \\\(\[^\n\r]\*\\\); \\\[tail call\\\]" 2 "optimized" } } */
+/* { dg-final { scan-tree-dump-times "  \[^\n\r]* = bar \\\(\[^\n\r]\*\\\); \\\[tail call\\\] \\\[must tail call\\\]" 1 "optimized" } } */
+/* { dg-final { scan-tree-dump-times "  \[^\n\r]* = freddy \\\(\[^\n\r]\*\\\); \\\[tail call\\\] \\\[must tail call\\\]" 1 "optimized" } } */
+/* { dg-final { scan-tree-dump-not "  (?:bar|freddy) \\\(\[^\n\r]\*\\\); \\\[tail call\\\]" "optimized" } } */
 
 __attribute__ ((noipa)) void
 foo (int x)
diff --git a/gcc/tree-ssa-propagate.cc b/gcc/tree-ssa-propagate.cc
index 94d4401f54a..ec206894821 100644
--- a/gcc/tree-ssa-propagate.cc
+++ b/gcc/tree-ssa-propagate.cc
@@ -870,7 +870,7 @@ substitute_and_fold_dom_walker::before_dom_children (basic_block bb)
 	}
       /* Also fold if we want to fold all statements.  */
       else if (substitute_and_fold_engine->fold_all_stmts
-	  && fold_stmt (&i, follow_single_use_edges))
+	       && fold_stmt (&i, follow_single_use_edges))
 	{
 	  did_replace = true;
 	  stmt = gsi_stmt (i);
@@ -1081,6 +1081,13 @@ may_propagate_copy (tree dest, tree orig, bool dest_not_abnormal_phi_edge_p)
   if (TREE_CODE (dest) == SSA_NAME && virtual_operand_p (dest))
     return false;
 
+  /* Keep lhs of [[gnu::musttail]] calls as is, those need to be still
+     tail callable.  */
+  if (TREE_CODE (dest) == SSA_NAME
+      && is_gimple_call (SSA_NAME_DEF_STMT (dest))
+      && gimple_call_must_tail_p (as_a <gcall *> (SSA_NAME_DEF_STMT (dest))))
+    return false;
+
   /* Anything else is OK.  */
   return true;
 }