From 6b8a8c9fd68c5dabaec5ddbc25efeade44f37a14 Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Mon, 17 Feb 2025 15:53:11 +0100
Subject: [PATCH] tree-optimization/98845 - ICE with tail-merging and DCE/DSE
 disabled

The following shows that tail-merging will make dead SSA defs live
in paths where it wasn't before, possibly introducing UB or as
in this case, uses of abnormals that eventually fail coalescing
later.  The fix is to register such defs for stmt comparison.

	PR tree-optimization/98845
	* tree-ssa-tail-merge.cc (stmt_local_def): Consider a
	def with no uses not local.

	* gcc.dg/pr98845.c: New testcase.
	* gcc.dg/pr81192.c: Adjust.
---
 gcc/testsuite/gcc.dg/pr81192.c |  6 +++++-
 gcc/testsuite/gcc.dg/pr98845.c | 33 +++++++++++++++++++++++++++++++++
 gcc/tree-ssa-tail-merge.cc     |  8 ++++++++
 3 files changed, 46 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr98845.c

diff --git a/gcc/testsuite/gcc.dg/pr81192.c b/gcc/testsuite/gcc.dg/pr81192.c
index c46ac18fd9af..87a7a7a19c80 100644
--- a/gcc/testsuite/gcc.dg/pr81192.c
+++ b/gcc/testsuite/gcc.dg/pr81192.c
@@ -25,12 +25,16 @@ void __GIMPLE(ssa, startwith("pre")) fn2   ()
   if (j_6(D) != _Literal (int)2147483647)
     goto __BB4;
   else
-    goto __BB5;
+    goto __BB9;
 
   __BB(4):
   iftmp2_8 = j_6(D) + _Literal (int)1;
   goto __BB5;
 
+  __BB(9):
+  iftmp2_8 = j_6(D) + _Literal (int)1;
+  goto __BB5;
+
   __BB(5):
   b_lsm6_10 = _Literal (int)2147483647;
   goto __BB6;
diff --git a/gcc/testsuite/gcc.dg/pr98845.c b/gcc/testsuite/gcc.dg/pr98845.c
new file mode 100644
index 000000000000..074c979678f9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr98845.c
@@ -0,0 +1,33 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-tree-dce -fno-tree-dse" } */
+
+int n;
+
+__attribute__ ((returns_twice)) void
+foo (void);
+
+void
+bar (void);
+
+void
+quux (int x)
+{
+  if (x)
+    ++x;
+  else
+    {
+      if (n)
+        {
+          x = 1;
+          foo ();
+        }
+      else
+        bar ();
+
+      if (n)
+        {
+          ++x;
+          ++n;
+        }
+    }
+}
diff --git a/gcc/tree-ssa-tail-merge.cc b/gcc/tree-ssa-tail-merge.cc
index d897970079ce..857e91c206b3 100644
--- a/gcc/tree-ssa-tail-merge.cc
+++ b/gcc/tree-ssa-tail-merge.cc
@@ -336,10 +336,13 @@ stmt_local_def (gimple *stmt)
 
   def_bb = gimple_bb (stmt);
 
+  bool any_use = false;
   FOR_EACH_IMM_USE_FAST (use_p, iter, val)
     {
       if (is_gimple_debug (USE_STMT (use_p)))
 	continue;
+
+      any_use = true;
       bb = gimple_bb (USE_STMT (use_p));
       if (bb == def_bb)
 	continue;
@@ -351,6 +354,11 @@ stmt_local_def (gimple *stmt)
       return false;
     }
 
+  /* When there is no use avoid making the stmt live on other paths.
+     This can happen with DCE disabled or not done as seen in PR98845.  */
+  if (!any_use)
+    return false;
+
   return true;
 }
 
-- 
2.47.2