[gcc r15-7602] tree-optimization/98845 - ICE with tail-merging and DCE/DSE disabled

[Richard Biener via Gcc-cvs]

https://gcc.gnu.org/g:6b8a8c9fd68c5dabaec5ddbc25efeade44f37a14

commit r15-7602-g6b8a8c9fd68c5dabaec5ddbc25efeade44f37a14
Author: Richard Biener <rguent...@suse.de>
Date:   Mon Feb 17 15:53:11 2025 +0100

    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.

Diff:
---
 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(-)

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;
 }