[PATCH v2] Fix PR79908

[Bill Schmidt]

Hi,

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79908 shows a case where
pass_stdarg ICEs attempting to gimplify a COMPLEX_EXPR with side
effects as an lvalue.  This occurs when the LHS of a VA_ARG has been
cast away.  This patch, credit to Richard Biener, uses
force_gimple_operand to instantiate the necessary side effects rather
than gimplify_expr using is_gimple_lvalue.  The test case is taken
wholesale from the bug report.

Bootstrapped and tested on powerpc64le-unknown-linux-gnu with no
regressions.  Is this ok for trunk?

Thanks,
Bill


[gcc]

2017-03-20  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
            Richard Biener  <rguenth@suse.com>

	PR tree-optimization/79908
	* tree-stdarg.c (expand_ifn_va_arg_1): For a VA_ARG whose LHS has
	been cast away, use force_gimple_operand to construct the side
	effects.

[gcc/testsuite]

2017-03-20  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
            Richard Biener  <rguenther@suse.de>

	PR tree-optimization/79908
	* gcc.dg/torture/pr79908.c: New file.


Index: gcc/testsuite/gcc.dg/torture/pr79908.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr79908.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/torture/pr79908.c	(working copy)
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+
+/* Used to fail in the stdarg pass before fix for PR79908.  */
+
+typedef __builtin_va_list __gnuc_va_list;
+typedef __gnuc_va_list va_list;
+
+void testva (int n, ...)
+{
+  va_list ap;
+  _Complex int i = __builtin_va_arg (ap, _Complex int);
+}
Index: gcc/tree-stdarg.c
===================================================================
--- gcc/tree-stdarg.c	(revision 246286)
+++ gcc/tree-stdarg.c	(working copy)
@@ -33,6 +33,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimple-iterator.h"
 #include "gimple-walk.h"
 #include "gimplify.h"
+#include "gimplify-me.h"
 #include "tree-into-ssa.h"
 #include "tree-cfg.h"
 #include "tree-stdarg.h"
@@ -1058,12 +1059,16 @@ expand_ifn_va_arg_1 (function *fun)
 	    gimplify_assign (lhs, expr, &pre);
 	  }
 	else
-	  gimplify_expr (&expr, &pre, &post, is_gimple_lvalue, fb_lvalue);
+	  {
+	    gimple_seq tmp_seq;
+	    force_gimple_operand (expr, &tmp_seq, false, NULL_TREE);
+	    gimple_seq_add_seq_without_update (&pre, tmp_seq);
+	  }
 
 	input_location = saved_location;
 	pop_gimplify_context (NULL);
 
-	gimple_seq_add_seq (&pre, post);
+	gimple_seq_add_seq_without_update (&pre, post);
 	update_modified_stmts (pre);
 
 	/* Add the sequence after IFN_VA_ARG.  This splits the bb right
@@ -1072,11 +1077,10 @@ expand_ifn_va_arg_1 (function *fun)
 	gimple_find_sub_bbs (pre, &i);
 
 	/* Remove the IFN_VA_ARG gimple_call.  It's the last stmt in the
-	   bb.  */
+	   bb if we added any stmts.  */
 	unlink_stmt_vdef (stmt);
 	release_ssa_name_fn (fun, gimple_vdef (stmt));
 	gsi_remove (&i, true);
-	gcc_assert (gsi_end_p (i));
 
 	/* We're walking here into the bbs which contain the expansion of
 	   IFN_VA_ARG, and will not contain another IFN_VA_ARG that needs