Re: PR 18501: Run uninitialized warnings pass before DCE

[Diego Novillo <dnovillo at redhat dot com>]

Richard Henderson wrote:

> Probably not too bad, and probably still better results
> than some earlier 3.x releases.
OK, I've xfailed the other tests and opened and enhancement PR.  I will 
be committing this patch.  Bootstrapped and tested x86, x86-64, alpha 
and ppc.


Diego.
2004-12-17  Diego Novillo  <dnovillo@redhat.com>

	tree-optimization/18501
	* tree-optimize.c (init_tree_optimization_passes): Run
	pass_late_warn_uninitialized before the last DCE run.

testsuite/ChangeLog:

	* gcc.dg/pr18501.c: New test.
	* gcc.dg/uninit-5.c: XFAIL.
	* gcc.dg/uninit-9.c: XFAIL.

Index: tree-optimize.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-optimize.c,v
retrieving revision 2.65
diff -d -c -p -u -r2.65 tree-optimize.c
--- tree-optimize.c	30 Nov 2004 15:38:33 -0000	2.65
+++ tree-optimize.c	17 Dec 2004 22:14:39 -0000
@@ -381,12 +381,21 @@ init_tree_optimization_passes (void)
   NEXT_PASS (pass_loop);
   NEXT_PASS (pass_dominator);
   NEXT_PASS (pass_redundant_phi);
+  /* FIXME: If DCE is not run before checking for uninitialized uses,
+     we may get false warnings (e.g., testsuite/gcc.dg/uninit-5.c).
+     However, this also causes us to misdiagnose cases that should be
+     real warnings (e.g., testsuite/gcc.dg/pr18501.c).
+     
+     To fix the false positives in uninit-5.c, we would have to
+     account for the predicates protecting the set and the use of each
+     variable.  Using a representation like Gated Single Assignment
+     may help.  */
+  NEXT_PASS (pass_late_warn_uninitialized);
   NEXT_PASS (pass_cd_dce);
   NEXT_PASS (pass_dse);
   NEXT_PASS (pass_forwprop);
   NEXT_PASS (pass_phiopt);
   NEXT_PASS (pass_tail_calls);
-  NEXT_PASS (pass_late_warn_uninitialized);
   NEXT_PASS (pass_del_ssa);
   NEXT_PASS (pass_nrv);
   NEXT_PASS (pass_remove_useless_vars);
Index: testsuite/gcc.dg/pr18501.c
===================================================================
RCS file: testsuite/gcc.dg/pr18501.c
diff -N testsuite/gcc.dg/pr18501.c
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ testsuite/gcc.dg/pr18501.c	17 Dec 2004 22:14:45 -0000
@@ -0,0 +1,20 @@
+/* Expected uninitialized variable warning.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O -Wuninitialized" } */
+
+unsigned bmp_iter_set ();
+int something (void);
+
+void
+bitmap_print_value_set (void)
+{
+  unsigned first;	/* { dg-warning "may be used" "conditional in loop" } */
+  
+  for (; bmp_iter_set (); )
+    {
+      if (!first)
+	something ();
+      first = 0;
+    }
+}
Index: testsuite/gcc.dg/uninit-5.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/testsuite/gcc.dg/uninit-5.c,v
retrieving revision 1.3
diff -d -c -p -u -r1.3 uninit-5.c
--- testsuite/gcc.dg/uninit-5.c	13 May 2004 06:40:49 -0000	1.3
+++ testsuite/gcc.dg/uninit-5.c	17 Dec 2004 22:14:45 -0000
@@ -9,7 +9,7 @@ extern void foo(void);
 void
 func1(int cond)
 {
-    int x;  /* { dg-bogus "x" "uninitialized variable warning" } */
+    int x;  /* { dg-bogus "x" "uninitialized variable warning" { xfail *-*-* } } */
 
     if(cond)
 	x = 1;
@@ -23,7 +23,7 @@ func1(int cond)
 void
 func2 (int cond)
 {
-    int x;  /* { dg-bogus "x" "uninitialized variable warning" } */
+    int x;  /* { dg-bogus "x" "uninitialized variable warning" { xfail *-*-* } } */
     int flag = 0;
 
     if(cond)
Index: testsuite/gcc.dg/uninit-9.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/testsuite/gcc.dg/uninit-9.c,v
retrieving revision 1.3
diff -d -c -p -u -r1.3 uninit-9.c
--- testsuite/gcc.dg/uninit-9.c	13 May 2004 06:40:49 -0000	1.3
+++ testsuite/gcc.dg/uninit-9.c	17 Dec 2004 22:14:45 -0000
@@ -23,7 +23,7 @@ func(struct foo *list, int count)
 {
     int n_clobbers = 0;
     int i;
-    struct foo **clob_list;   /* { dg-bogus "clob_list" "uninitialized variable warning" } */
+    struct foo **clob_list;   /* { dg-bogus "clob_list" "uninitialized variable warning" { xfail *-*-* } } */
 
     if(list[0].type == PARALLEL)
     {