From: Tamar Christina <tamar.christina@arm.com>
Date: Fri, 12 Jan 2024 15:25:58 +0000 (+0000)
Subject: middle-end: thread through existing LCSSA variable for alternative exits too [PR113237]
X-Git-Tag: basepoints/gcc-15~2943
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=99c0a540d6689ede068f9ba98af6f38c3cd71362;p=thirdparty%2Fgcc.git

middle-end: thread through existing LCSSA variable for alternative exits too [PR113237]

Builing on top of the previous patch, similar to when we have a single exit if
we have a case where all exits are considered early exits and there are existing
non virtual phi then in order to maintain LCSSA we have to use the existing PHI
variables.  We can't simply clear them and just rebuild them because the order
of the PHIs in the main exit must match the original exit for when we add the
skip_epilog guard.

But the infrastructure is already in place to maintain them, we just have to use
the right value.

gcc/ChangeLog:

	PR tree-optimization/113237
	* tree-vect-loop-manip.cc (slpeel_tree_duplicate_loop_to_edge_cfg): Use
	existing LCSSA variable for exit when all exits are early break.

gcc/testsuite/ChangeLog:

	PR tree-optimization/113237
	* gcc.dg/vect/vect-early-break_98-pr113237.c: New test.
---

diff --git a/gcc/testsuite/gcc.dg/vect/vect-early-break_98-pr113237.c b/gcc/testsuite/gcc.dg/vect/vect-early-break_98-pr113237.c
new file mode 100644
index 000000000000..e6d150b571f7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-early-break_98-pr113237.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-add-options vect_early_break } */
+/* { dg-require-effective-target vect_early_break } */
+/* { dg-require-effective-target vect_int } */
+
+long Perl_pp_split_limit;
+int Perl_block_gimme();
+int Perl_pp_split() {
+  char strend;
+  long iters;
+  int gimme = Perl_block_gimme();
+  while (--Perl_pp_split_limit) {
+    if (gimme)
+      iters++;
+    if (strend)
+      break;
+  }
+  if (iters)
+    return 0;
+}
diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index da64738c7101..2a1f9cd77071 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -1697,10 +1697,15 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop, edge loop_exit,
 		 virtual operands we have to keep the original link.   Virtual
 		 operands don't all become the same because we'll corrupt the
 		 vUSE chains among others.  */
-	      if (peeled_iters && !virtual_operand_p (new_arg))
+	      if (peeled_iters)
 		{
 		  tree tmp_arg = gimple_phi_result (from_phi);
-		  if (!new_phi_args.get (tmp_arg))
+		  /* Similar to the single exit case, If we have an existing
+		     LCSSA variable thread through the original value otherwise
+		     skip it and directly use the final value.  */
+		  if (tree *res = new_phi_args.get (tmp_arg))
+		    new_arg = *res;
+		  else if (!virtual_operand_p (new_arg))
 		    new_arg = tmp_arg;
 		}