fix latent bootstrap-debug issue (modref, tree-inline, tree jump-threading)

Alexandre Oliva
Sat Aug 21 02:50:15 GMT 2021

I've hit a bootstrap-debug error involving large subprograms in
gcc/ada/sem_ch12.adb.  I'm afraid I couldn't narrow it down to a
reasonable testcase.

thread1 made different decisions about a block containing a
builtin_eh_filter call because in one compilation, estimate_num_insns
found a cgraph_node for the builtin and could thus get to the
is_simple_builtin test, but in the other it didn't.  With different
insn counts, one stage jump-threaded and the other didn't, and the
resulting code diverged quite a bit.

The reason the builtin had a cgraph_node in one case but not the other
was that modref got a chance to analyze the builtin call when it was
the first stmt in the block, and that created the cgraph_node.
However, when it was preceded by debug stmts, the loop in
analyze_function was cut short after the first debug stmt, because the
summary so far was not useful.

This patch fixes both issues: skip debug stmts in the analyze_function
loop, so as to prevent them from affecting any decisions in the loop,
and enable the insn count estimator to get to the is_simple_builtin
test when a cgraph_node has not been created for the builtin.

Regstrapped on x86_64-linux-gnu.  Ok to install?

for  gcc/ChangeLog

	* ipa-modref.c (analyze_function): Skip debug stmts.
	* tree-inline.c (estimate_num_insn): Consider builtins even
	without a cgraph_node.
 gcc/ipa-modref.c  |    3 ++-
 gcc/tree-inline.c |    4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/gcc/ipa-modref.c b/gcc/ipa-modref.c
index fafd804d4bae4..f0cddbb077aaa 100644
--- a/gcc/ipa-modref.c
+++ b/gcc/ipa-modref.c
@@ -2108,7 +2108,8 @@ analyze_function (function *f, bool ipa)
   FOR_EACH_BB_FN (bb, f)
       gimple_stmt_iterator si;
-      for (si = gsi_after_labels (bb); !gsi_end_p (si); gsi_next (&si))
+      for (si = gsi_start_nondebug_after_labels_bb (bb);
+	   !gsi_end_p (si); gsi_next_nondebug (&si))
 	  if (!analyze_stmt (summary, summary_lto,
 			     gsi_stmt (si), ipa, &recursive_calls)
diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
index d0e9f52d5f138..636130fe0019e 100644
--- a/gcc/tree-inline.c
+++ b/gcc/tree-inline.c
@@ -4436,8 +4436,8 @@ estimate_num_insns (gimple *stmt, eni_weights *weights)
 	    /* Do not special case builtins where we see the body.
 	       This just confuse inliner.  */
 	    struct cgraph_node *node;
-	    if (!(node = cgraph_node::get (decl))
-		|| node->definition)
+	    if ((node = cgraph_node::get (decl))
+		&& node->definition)
 	    /* For buitins that are likely expanded to nothing or
 	       inlined do not account operand costs.  */

Alexandre Oliva, happy hacker      
   Free Software Activist                       GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts.  Ask me about <>

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