middle-end/40635 - SSA update losing PHI arg loations

The following fixes an issue where SSA update loses PHI argument
locations when updating PHI nodes it didn't create as part of the
SSA update.  For the case where the reaching def is the same as
the current argument opt to do nothing and for the case where the
PHI argument already has a location keep that (that's an indication
the PHI node wasn't created as part of the update SSA process).

	PR middle-end/40635
	* tree-into-ssa.cc (rewrite_update_phi_arguments): Only
	update the argument when the reaching definition is different
	from the current argument.  Keep an existing argument
	location.

	* gcc.dg/uninit-pr40635.c: New testcase.

2 files changed, 40 insertions, 4 deletions

diff --git a/gcc/testsuite/gcc.dg/uninit-pr40635.c b/gcc/testsuite/gcc.dg/uninit-pr40635.c
new file mode 100644
index 0000000..fab7c3d4
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/uninit-pr40635.c
@@ -0,0 +1,33 @@
+/* { dg-do compile } */
+/* { dg-options "-O -Wuninitialized" } */
+
+struct hostent {
+    char **h_addr_list;
+};
+struct hostent *gethostbyname(const char*);
+int socket(void);
+int close(int);
+int connect(int, const char*);
+
+int get_tcp_socket(const char *machine)
+{
+  struct hostent *hp;
+  int s42, x;
+  char **addr;
+
+  hp = gethostbyname(machine);
+  x = 0;
+  for (addr = hp->h_addr_list; *addr; addr++)
+    {
+      s42 = socket();
+      if (s42 < 0)
+	return -1;
+      x = connect(s42, *addr);
+      if (x == 0)
+	break;
+      close(s42);
+    }
+  if (x < 0)
+    return -1;
+  return s42;  /* { dg-warning "uninitialized" } */
+}
diff --git a/gcc/tree-into-ssa.cc b/gcc/tree-into-ssa.cc
index f21ed2b..9a2417d 100644
--- a/gcc/tree-into-ssa.cc
+++ b/gcc/tree-into-ssa.cc
@@ -2110,7 +2110,6 @@ rewrite_update_phi_arguments (basic_block bb)
 		 symbol we may find NULL arguments.  That's why we
 		 take the symbol from the LHS of the PHI node.  */
 	      reaching_def = get_reaching_def (lhs_sym);
-
 	    }
 	  else
 	    {
@@ -2122,8 +2121,9 @@ rewrite_update_phi_arguments (basic_block bb)
 		reaching_def = get_reaching_def (arg);
 	    }
 
-          /* Update the argument if there is a reaching def.  */
-	  if (reaching_def)
+	  /* Update the argument if there is a reaching def different
+	     from arg.  */
+	  if (reaching_def && reaching_def != arg)
 	    {
 	      location_t locus;
 	      int arg_i = PHI_ARG_INDEX_FROM_USE (arg_p);
@@ -2133,6 +2133,10 @@ rewrite_update_phi_arguments (basic_block bb)
 	      /* Virtual operands do not need a location.  */
 	      if (virtual_operand_p (reaching_def))
 		locus = UNKNOWN_LOCATION;
+	      /* If SSA update didn't insert this PHI the argument
+		 might have a location already, keep that.  */
+	      else if (gimple_phi_arg_has_location (phi, arg_i))
+		locus = gimple_phi_arg_location (phi, arg_i);
 	      else
 		{
 		  gimple *stmt = SSA_NAME_DEF_STMT (reaching_def);
@@ -2150,7 +2154,6 @@ rewrite_update_phi_arguments (basic_block bb)
 	      gimple_phi_arg_set_location (phi, arg_i, locus);
 	    }
 
-
 	  if (e->flags & EDGE_ABNORMAL)
 	    SSA_NAME_OCCURS_IN_ABNORMAL_PHI (USE_FROM_PTR (arg_p)) = 1;
 	}