PR tree-optimization/84468 - bogus -Wstringop-truncation despite assignment after conditional strncpy

gcc/testsuite/ChangeLog:

	PR tree-optimization/84468
	* gcc.dg/Wstringop-truncation.c: New test.

gcc/ChangeLog:

	PR tree-optimization/84468
	* tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Also consider successor
	basic blocks.

Index: gcc/tree-ssa-strlen.c
===================================================================
--- gcc/tree-ssa-strlen.c	(revision 257796)
+++ gcc/tree-ssa-strlen.c	(working copy)
@@ -1851,8 +1851,18 @@ maybe_diag_stxncpy_trunc (gimple_stmt_iterator gsi
      avoid the truncation warning.  */
   gsi_next_nondebug (&gsi);
   gimple *next_stmt = gsi_stmt (gsi);
+  if (!next_stmt)
+    {
+      /* When there is no statement in the same basic block check
+	 the immediate successor block.  */
+      basic_block bb = gimple_bb (stmt);
+      basic_block nextbb
+	= EDGE_COUNT (bb->succs) ? EDGE_SUCC (bb, 0)->dest : NULL;
+      gimple_stmt_iterator it = gsi_start_bb (nextbb);
+      next_stmt = gsi_stmt (it);
+    }
 
-  if (!gsi_end_p (gsi) && is_gimple_assign (next_stmt))
+  if (next_stmt && is_gimple_assign (next_stmt))
     {
       tree lhs = gimple_assign_lhs (next_stmt);
       tree_code code = TREE_CODE (lhs);
Index: gcc/testsuite/gcc.dg/Wstringop-truncation.c
===================================================================
--- gcc/testsuite/gcc.dg/Wstringop-truncation.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/Wstringop-truncation.c	(working copy)
@@ -0,0 +1,116 @@
+/* PR tree-optimization/84468 - Inconsistent -Wstringop-truncation warnings
+   with -O2
+   { dg-do compile }
+   { dg-options "-O2 -Wstringop-truncation -ftrack-macro-expansion=0" }  */
+
+#define strncpy __builtin_strncpy
+
+struct A
+{
+  char a[4];
+};
+
+void no_pred_succ (struct A *p, const struct A *q)
+{
+  strncpy (p->a, q->a, sizeof p->a - 1);      /* { dg-warning "\\\[-Wstringop-truncation" } */
+}
+
+
+void no_succ (struct A *p, const struct A *q)
+{
+  if (q->a)
+    strncpy (p->a, q->a, sizeof p->a - 1);    /* { dg-warning "\\\[-Wstringop-truncation" } */
+}
+
+
+void succ (struct A *p, const struct A *q)
+{
+  /* Verify that the assignment suppresses the warning for the conditional
+     strcnpy call.  The conditional should be folded to true since the
+     address of an array can never be null (see bug 84470).  */
+  if (q->a)
+    strncpy (p->a, q->a, sizeof p->a - 1);    /* { dg-bogus "\\\[-Wstringop-truncation" } */
+
+  p->a[sizeof p->a - 1] = 0;
+}
+
+
+void succ_2 (struct A *p, const struct A *q, int i)
+{
+  /* Same as above but with a conditional that cannot be eliminated.  */
+  if (i < 0)
+    strncpy (p->a, q->a, sizeof p->a - 1);    /* { dg-bogus "\\\[-Wstringop-truncation" } */
+
+  p->a[sizeof p->a - 1] = 0;
+}
+
+
+int next_succ (struct A *p, const struct A *q, int i, int j)
+{
+  /* Same as above but with a nested conditionals with else clauses.  */
+  if (i < 0)
+    {
+      if (j < 0)
+	strncpy (p->a, q->a, sizeof p->a - 1);    /* { dg-bogus "\\\[-Wstringop-truncation" } */
+    }
+  else
+    __builtin_strcpy (p->a, q->a);
+
+  p->a[sizeof p->a - 1] = 0;
+  return 0;
+}
+
+
+int next_succ_1 (struct A *p, const struct A *q, int i, int j)
+{
+  /* Same as above but with a nested conditionals with else clauses.  */
+  if (i < 0)
+    {
+      if (j < 0)
+	strncpy (p->a, q->a, sizeof p->a - 1);    /* { dg-bogus "\\\[-Wstringop-truncation" } */
+      else
+	strncpy (p->a, q->a, sizeof p->a - 2);    /* { dg-bogus "\\\[-Wstringop-truncation" } */
+    }
+
+  p->a[sizeof p->a - 2] = 0;
+  return 1;
+}
+
+
+int next_succ_2 (struct A *p, const struct A *q, int i, int j)
+{
+  /* Same as above but with a nested conditionals with else clauses.  */
+  if (i < 0)
+    {
+      if (j < 0)
+	strncpy (p->a, q->a, sizeof p->a - 1);    /* { dg-bogus "\\\[-Wstringop-truncation" } */
+      else
+	strncpy (p->a, q->a, sizeof p->a - 2);    /* { dg-bogus "\\\[-Wstringop-truncation" } */
+    }
+  else
+    __builtin_strcpy (p->a, q->a);
+
+  p->a[sizeof p->a - 2] = 0;
+  return 2;
+}
+
+
+void cond_succ_warn (struct A *p, const struct A *q, int i)
+{
+  /* Verify that a conditional assignment doesn't suppress the warning.  */
+  strncpy (p->a, q->a, sizeof p->a - 1);      /* { dg-warning "\\\[-Wstringop-truncation" } */
+
+  if (i < 0)
+    p->a[sizeof p->a - 1] = 0;
+}
+
+void cond_succ_nowarn (struct A *p, const struct A *q)
+{
+  /* Verify that distinct but provably equivalent conditionals are
+     recognized and don't trigger the warning.  */
+  if (p != q)
+    strncpy (p->a, q->a, sizeof p->a - 1);
+
+  if (p->a != q->a)
+    p->a[sizeof p->a - 1] = 0;
+}
