[gcc r12-10553] middle-end/40635 - SSA update losing PHI arg loations

[Richard Biener]

https://gcc.gnu.org/g:844ff32c04a4e36bf69f3878634d9f50aec3a332

commit r12-10553-g844ff32c04a4e36bf69f3878634d9f50aec3a332
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Dec 5 16:03:21 2022 +0100

    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.
    
    (cherry picked from commit 0d14720f93a8139a7f234b2762c361e8e5da99cc)

Diff:
---
 gcc/testsuite/gcc.dg/uninit-pr40635.c | 33 +++++++++++++++++++++++++++++++++
 gcc/tree-into-ssa.cc                  | 11 +++++++----
 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 000000000000..fab7c3d49d9d
--- /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 dd41b1b77b7a..fa53beec2abf 100644
--- a/gcc/tree-into-ssa.cc
+++ b/gcc/tree-into-ssa.cc
@@ -2107,7 +2107,6 @@ 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
 	    {
@@ -2119,8 +2118,9 @@ 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);
@@ -2130,6 +2130,10 @@ 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);
@@ -2147,7 +2151,6 @@ 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;
 	}