[gcc r13-4713] into-ssa: Fix emitting debug stmts after asm goto [PR108095]

[gcc r13-4713] into-ssa: Fix emitting debug stmts after asm goto [PR108095]

[Jakub Jelinek]

https://gcc.gnu.org/g:bf3ce6f84a7a994a0fc87419b383b9ce4efed442

commit r13-4713-gbf3ce6f84a7a994a0fc87419b383b9ce4efed442
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Dec 15 09:26:44 2022 +0100

    into-ssa: Fix emitting debug stmts after asm goto [PR108095]
    
    The following testcase ICEs, because ccp1 replaced
      s.0_1 = &s;
      __asm__ goto("" : "=r" MEM[(T *)s.0_1] :  :  : "lab" lab);
    with
      __asm__ goto("" : "=r" s :  :  : "lab" lab);
    and because s is no longer addressable, we are rewriting it into
    ssa and want
      __asm__ goto("" : "=r" s_7 :  :  : "lab" lab);
    plus debug stmt
      # DEBUG s => s_7
    The code assumes that there is at most one non-EH edge in that
    case, but with the addition of outputs to asm goto that is no longer the
    case, we can have many outgoing edges.
    
    The patch keeps the checking assertion that there is at most one such
    edge for everything but asm goto, but moves the addition of the debug
    stmt into the loop, so that it can be added on all edges where it is
    possible, not just one of them.
    
    Furthermore, looking at gsi_insert_on_edge_immediate
    -> gimple_find_edge_insert_loc, the conditions to insert stmt there
    to the destination block are
      if (single_pred_p (dest)
          && gimple_seq_empty_p (phi_nodes (dest))
          && dest != EXIT_BLOCK_PTR_FOR_FN (cfun))
    (plus there is code to insert it in the previous block but that is
    never true when the pred is known to be stmt_ends_bb_p), while
    mayube_register_def was just checking
                     if (ef && single_pred_p (ef->dest)
                         && ef->dest != EXIT_BLOCK_PTR_FOR_FN (cfun))
    so if for whatever reason ef->dest had any PHIs, we'd split the
    edge for -g and not for -g0, something we must avoid for -fcompare-debug
    stability.  So, I've added the no phi_nodes check too.
    
    2022-12-15  Jakub Jelinek  <jakub@redhat.com>
    
            PR tree-optimization/108095
            * tree-into-ssa.cc (maybe_register_def): Insert debug stmt
            on all non-EH edges from asm goto if they have a single
            predecessor rather than asserting there is at most one such edge.
            Test whether there are no PHI nodes next to the single predecessor
            test.
    
            * gcc.dg/pr108095.c: New test.

Diff:
---
 gcc/testsuite/gcc.dg/pr108095.c | 15 ++++++++++
 gcc/tree-into-ssa.cc            | 64 ++++++++++++++++++++++++-----------------
 2 files changed, 53 insertions(+), 26 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/pr108095.c b/gcc/testsuite/gcc.dg/pr108095.c
new file mode 100644
index 00000000000..fb76caae72e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr108095.c
@@ -0,0 +1,15 @@
+/* PR tree-optimization/108095 */
+/* { dg-do compile } */
+/* { dg-options "-Os -g" } */
+
+int v;
+typedef unsigned T;
+
+void
+foo (void)
+{
+  unsigned s;
+  asm goto ("" : "=r" (*(T *) &s) : : : lab);
+  v = 0;
+lab:
+}
diff --git a/gcc/tree-into-ssa.cc b/gcc/tree-into-ssa.cc
index 9a2417d2b0b..ebe7e699277 100644
--- a/gcc/tree-into-ssa.cc
+++ b/gcc/tree-into-ssa.cc
@@ -1934,9 +1934,8 @@ maybe_register_def (def_operand_p def_p, gimple *stmt,
 	  tree tracked_var = target_for_debug_bind (sym);
 	  if (tracked_var)
 	    {
-	      gimple *note = gimple_build_debug_bind (tracked_var, def, stmt);
-	      /* If stmt ends the bb, insert the debug stmt on the single
-		 non-EH edge from the stmt.  */
+	      /* If stmt ends the bb, insert the debug stmt on the non-EH
+		 edge(s) from the stmt.  */
 	      if (gsi_one_before_end_p (gsi) && stmt_ends_bb_p (stmt))
 		{
 		  basic_block bb = gsi_bb (gsi);
@@ -1945,33 +1944,46 @@ maybe_register_def (def_operand_p def_p, gimple *stmt,
 		  FOR_EACH_EDGE (e, ei, bb->succs)
 		    if (!(e->flags & EDGE_EH))
 		      {
-			gcc_checking_assert (!ef);
+			/* asm goto can have multiple non-EH edges from the
+			   stmt.  Insert on all of them where it is
+			   possible.  */
+			gcc_checking_assert (!ef || (gimple_code (stmt)
+						     == GIMPLE_ASM));
 			ef = e;
+			/* If there are other predecessors to ef->dest, then
+			   there must be PHI nodes for the modified
+			   variable, and therefore there will be debug bind
+			   stmts after the PHI nodes.  The debug bind notes
+			   we'd insert would force the creation of a new
+			   block (diverging codegen) and be redundant with
+			   the post-PHI bind stmts, so don't add them.
+
+			   As for the exit edge, there wouldn't be redundant
+			   bind stmts, but there wouldn't be a PC to bind
+			   them to either, so avoid diverging the CFG.  */
+			if (e
+			    && single_pred_p (e->dest)
+			    && gimple_seq_empty_p (phi_nodes (e->dest))
+			    && e->dest != EXIT_BLOCK_PTR_FOR_FN (cfun))
+			  {
+			    /* If there were PHI nodes in the node, we'd
+			       have to make sure the value we're binding
+			       doesn't need rewriting.  But there shouldn't
+			       be PHI nodes in a single-predecessor block,
+			       so we just add the note.  */
+			    gimple *note
+			      = gimple_build_debug_bind (tracked_var, def,
+							 stmt);
+			    gsi_insert_on_edge_immediate (ef, note);
+			  }
 		      }
-		  /* If there are other predecessors to ef->dest, then
-		     there must be PHI nodes for the modified
-		     variable, and therefore there will be debug bind
-		     stmts after the PHI nodes.  The debug bind notes
-		     we'd insert would force the creation of a new
-		     block (diverging codegen) and be redundant with
-		     the post-PHI bind stmts, so don't add them.
-
-		     As for the exit edge, there wouldn't be redundant
-		     bind stmts, but there wouldn't be a PC to bind
-		     them to either, so avoid diverging the CFG.  */
-		  if (ef && single_pred_p (ef->dest)
-		      && ef->dest != EXIT_BLOCK_PTR_FOR_FN (cfun))
-		    {
-		      /* If there were PHI nodes in the node, we'd
-			 have to make sure the value we're binding
-			 doesn't need rewriting.  But there shouldn't
-			 be PHI nodes in a single-predecessor block,
-			 so we just add the note.  */
-		      gsi_insert_on_edge_immediate (ef, note);
-		    }
 		}
 	      else
-		gsi_insert_after (&gsi, note, GSI_SAME_STMT);
+		{
+		  gimple *note
+		    = gimple_build_debug_bind (tracked_var, def, stmt);
+		  gsi_insert_after (&gsi, note, GSI_SAME_STMT);
+		}
 	    }
 	}