[PATCH] ipa: Avoid excessive removing of SSAs (PR 113757)

[Martin Jambor <mjambor@suse.cz>]

Hi,

PR 113757 shows that the code which was meant to debug-reset and
remove SSAs defined by LHSs of calls redirected to
__builtin_unreachable can trigger also when speculative
devirtualization creates a call to a noreturn function (and since it
is noreturn, it does not bother dealing with its return value).

What is more, it seems that the code handling this case is not really
necessary.  I feel slightly idiotic about this because I have a
feeling that I added it because of a failing test-case but I can
neither find the testcase nor a reason why the code in
cgraph_edge::redirect_call_stmt_to_callee would not be sufficient (it
turns the SSA name into a default-def, a bit like IPA-SRA, but any
code dominated by a call to a noreturn is not dangerous when it comes
to its side-effects).  So this patch just removes the handling.

Bootstrapped and tested on x86_64-linux and ppc64le-linux.  I have also
LTO-bootstrapped and LTO-profilebootstrapped the patch on x86_64-linux.

OK for master?

Thanks,

Martin


gcc/ChangeLog:

2024-02-07  Martin Jambor  <mjambor@suse.cz>

	PR ipa/113757
	* tree-inline.cc (redirect_all_calls): Remove code adding SSAs to
	id->killed_new_ssa_names.

gcc/testsuite/ChangeLog:

2024-02-07  Martin Jambor  <mjambor@suse.cz>

	PR ipa/113757
	* g++.dg/ipa/pr113757.C: New test.
---
 gcc/testsuite/g++.dg/ipa/pr113757.C | 14 ++++++++++++++
 gcc/tree-inline.cc                  | 14 ++------------
 2 files changed, 16 insertions(+), 12 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/ipa/pr113757.C

diff --git a/gcc/testsuite/g++.dg/ipa/pr113757.C b/gcc/testsuite/g++.dg/ipa/pr113757.C
new file mode 100644
index 00000000000..885d4010a10
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ipa/pr113757.C
@@ -0,0 +1,14 @@
+// { dg-do compile }
+// { dg-options "-O2 -fPIC" }
+// { dg-require-effective-target fpic }
+
+long size();
+struct ll {  virtual int hh();  };
+ll  *slice_owner;
+int ll::hh() { __builtin_exit(0); }
+int nn() {
+  if (size())
+    return 0;
+  return slice_owner->hh();
+}
+int (*a)() = nn;
diff --git a/gcc/tree-inline.cc b/gcc/tree-inline.cc
index 75c10eb7dfc..cac41b4f031 100644
--- a/gcc/tree-inline.cc
+++ b/gcc/tree-inline.cc
@@ -2984,23 +2984,13 @@ redirect_all_calls (copy_body_data * id, basic_block bb)
       gimple *stmt = gsi_stmt (si);
       if (is_gimple_call (stmt))
 	{
-	  tree old_lhs = gimple_call_lhs (stmt);
 	  struct cgraph_edge *edge = id->dst_node->get_edge (stmt);
 	  if (edge)
 	    {
 	      if (!id->killed_new_ssa_names)
 		id->killed_new_ssa_names = new hash_set<tree> (16);
-	      gimple *new_stmt
-		= cgraph_edge::redirect_call_stmt_to_callee (edge,
-		    id->killed_new_ssa_names);
-	      if (old_lhs
-		  && TREE_CODE (old_lhs) == SSA_NAME
-		  && !gimple_call_lhs (new_stmt))
-		/* In case of IPA-SRA removing the LHS, the name should have
-		   been already added to the hash.  But in case of redirecting
-		   to builtin_unreachable it was not and the name still should
-		   be pruned from debug statements.  */
-		id->killed_new_ssa_names->add (old_lhs);
+	      cgraph_edge::redirect_call_stmt_to_callee (edge,
+		id->killed_new_ssa_names);
 
 	      if (stmt == last && id->call_stmt && maybe_clean_eh_stmt (stmt))
 		gimple_purge_dead_eh_edges (bb);
-- 
2.43.0