[RFC] Enable virtual operands at -O0

[Eric Botcazou <ebotcazou at adacore dot com>]

Hi,

I recently stumbled on the ??? comment in tree-ssa-uninit.c and wondered why 
virtual operands are not enabled at -O0.  As demonstrated by the attached 
patch, this would make it possible to unXFAIL a few uninit-*.c testcases.

Tested on x86_64-suse-linux.


	* tree-ssa-operands.c (create_vop_var): Set DECL_IGNORED_P.
	(append_use): Run at -O0.
	(append_vdef): Likewise.
	* tree-ssa-uninit.c (warn_uninitialized_vars): Remove obsolete comment.
testsuite/
	* gcc.dg/uninit-B-O0.c: Remove XFAIL.
	* gcc.dg/uninit-I-O0.c: Likewise.
	* gcc.dg/uninit-pr19430-O0.c: Remove some XFAILs.


-- 
Eric Botcazou

Index: tree-ssa-uninit.c
===================================================================
--- tree-ssa-uninit.c	(revision 209411)
+++ tree-ssa-uninit.c	(working copy)
@@ -210,7 +210,6 @@ warn_uninitialized_vars (bool warn_possi
 
 	  /* For memory the only cheap thing we can do is see if we
 	     have a use of the default def of the virtual operand.
-	     ???  Note that at -O0 we do not have virtual operands.
 	     ???  Not so cheap would be to use the alias oracle via
 	     walk_aliased_vdefs, if we don't find any aliasing vdef
 	     warn as is-used-uninitialized, if we don't find an aliasing
Index: testsuite/gcc.dg/uninit-I-O0.c
===================================================================
--- testsuite/gcc.dg/uninit-I-O0.c	(revision 209411)
+++ testsuite/gcc.dg/uninit-I-O0.c	(working copy)
@@ -3,6 +3,6 @@
 
 int sys_msgctl (void)
 {
-  struct { int mode; } setbuf;  /* { dg-warning "'setbuf\.mode' is used" {} { xfail *-*-* } } */
-  return setbuf.mode;
+  struct { int mode; } setbuf;
+  return setbuf.mode; /* { dg-warning "'setbuf\.mode' is used uninitialized in this function" } */
 }
Index: testsuite/gcc.dg/uninit-B-O0.c
===================================================================
--- testsuite/gcc.dg/uninit-B-O0.c	(revision 209411)
+++ testsuite/gcc.dg/uninit-B-O0.c	(working copy)
@@ -9,7 +9,7 @@ void
 baz (void)
 {
   int i;
-  if (i) /* { dg-warning "uninit" "uninit i warning" { xfail *-*-* } } */
+  if (i) /* { dg-warning "'i' is used uninitialized in this function" } */
     bar (i);
   foo (&i);
 }
Index: testsuite/gcc.dg/uninit-pr19430-O0.c
===================================================================
--- testsuite/gcc.dg/uninit-pr19430-O0.c	(revision 209411)
+++ testsuite/gcc.dg/uninit-pr19430-O0.c	(working copy)
@@ -16,10 +16,9 @@ foo (int i)
   return j;
 }
 
-
 int foo2( void ) {
-  int rc;  /* { dg-warning "'rc' is used uninitialized in this function" "uninitialized" { xfail *-*-* } 21 } */
-  return rc;
+  int rc;
+  return rc; /* { dg-warning "'rc' is used uninitialized in this function" } */
   *&rc = 0;
 }
 
@@ -29,7 +28,7 @@ void frob(int *pi);
 int main(void)
 {
   int i; 
-  printf("i = %d\n", i); /* { dg-warning "'i' is used uninitialized in this function" "uninitialized" { xfail *-*-* } 32 } */
+  printf("i = %d\n", i); /* { dg-warning "'i' is used uninitialized in this function" } */
   frob(&i);
 
   return 0;
@@ -38,6 +37,6 @@ int main(void)
 void foo3(int*);
 void bar3(void) { 
   int x; 
-  if(x) /* { dg-warning "'x' is used uninitialized in this function" "uninitialized" { xfail *-*-* } 41 } */
+  if(x) /* { dg-warning "'x' is used uninitialized in this function" } */
     foo3(&x); 
 }
Index: tree-ssa-operands.c
===================================================================
--- tree-ssa-operands.c	(revision 209411)
+++ tree-ssa-operands.c	(working copy)
@@ -166,6 +166,7 @@ create_vop_var (struct function *fn)
 			   get_identifier (".MEM"),
 			   void_type_node);
   DECL_ARTIFICIAL (global_var) = 1;
+  DECL_IGNORED_P (global_var) = 1;
   TREE_READONLY (global_var) = 0;
   DECL_EXTERNAL (global_var) = 1;
   TREE_STATIC (global_var) = 1;
@@ -477,9 +478,6 @@ append_use (tree *use_p)
 static inline void
 append_vdef (tree var)
 {
-  if (!optimize)
-    return;
-
   gcc_assert ((build_vdef == NULL_TREE
 	       || build_vdef == var)
 	      && (build_vuse == NULL_TREE
@@ -495,9 +493,6 @@ append_vdef (tree var)
 static inline void
 append_vuse (tree var)
 {
-  if (!optimize)
-    return;
-
   gcc_assert (build_vuse == NULL_TREE
 	      || build_vuse == var);