PR middle-end/79496 - call to snprintf with zero size eliminated with -Wformat-truncation=2

gcc/ChangeLog:

	PR middle-end/79496
	* gimple-ssa-sprintf.c (pass_sprintf_length::handle_gimple_call): Avoid
	clearing info.nowrite flag when snprintf size argument is a range.

gcc/testsuite/ChangeLog:

	PR middle-end/79496
	* gcc.dg/tree-ssa/builtin-snprintf-2.c: New test.

From-SVN: r245415

gcc/ChangeLog

+2017-02-13  Martin Sebor  <msebor@redhat.com>
+
+	PR middle-end/79496
+	* gimple-ssa-sprintf.c (pass_sprintf_length::handle_gimple_call): Avoid
+	clearing info.nowrite flag when snprintf size argument is a range.
+
 2017-02-13  Jakub Jelinek  <jakub@redhat.com>
 
 	* cprop.c (cprop_jump): Add missing space in string literal.

gcc/gimple-ssa-sprintf.c

@@ -3443,6 +3443,10 @@ pass_sprintf_length::handle_gimple_call (gimple_stmt_iterator *gsi)
 
   info.format = gimple_call_arg (info.callstmt, idx_format);
 
+  /* True when the destination size is constant as opposed to the lower
+     or upper bound of a range.  */
+  bool dstsize_cst_p = true;
+
   if (idx_dstsize == HOST_WIDE_INT_M1U)
     {
       /* For non-bounded functions like sprintf, determine the size
@@ -3483,8 +3487,8 @@ pass_sprintf_length::handle_gimple_call (gimple_stmt_iterator *gsi)
       else if (TREE_CODE (size) == SSA_NAME)
 	{
 	  /* Try to determine the range of values of the argument
-	     and use the greater of the two at -Wformat-level 1 and
-	     the smaller of them at level 2.  */
+	     and use the greater of the two at level 1 and the smaller
+	     of them at level 2.  */
 	  wide_int min, max;
 	  enum value_range_type range_type
 	    = get_range_info (size, &min, &max);
@@ -3495,6 +3499,11 @@ pass_sprintf_length::handle_gimple_call (gimple_stmt_iterator *gsi)
 		   ? wi::fits_uhwi_p (max) ? max.to_uhwi () : max.to_shwi ()
 		   : wi::fits_uhwi_p (min) ? min.to_uhwi () : min.to_shwi ());
 	    }
+
+	  /* The destination size is not constant.  If the function is
+	     bounded (e.g., snprintf) a lower bound of zero doesn't
+	     necessarily imply it can be eliminated.  */
+	  dstsize_cst_p = false;
 	}
     }
 
@@ -3511,7 +3520,7 @@ pass_sprintf_length::handle_gimple_call (gimple_stmt_iterator *gsi)
 	 without actually producing any.  Pretend the size is
 	 unlimited in this case.  */
       info.objsize = HOST_WIDE_INT_MAX;
-      info.nowrite = true;
+      info.nowrite = dstsize_cst_p;
     }
   else
     {

gcc/testsuite/ChangeLog

+2017-02-13  Martin Sebor  <msebor@redhat.com>
+
+	PR middle-end/79496
+	* gcc.dg/tree-ssa/builtin-snprintf-2.c: New test.
+
 2017-02-13  Jakub Jelinek  <jakub@redhat.com>
 
 	PR sanitizer/79341

gcc/testsuite/gcc.dg/tree-ssa/builtin-snprintf-2.c

+/* PR middle-end/79496 - call to snprintf with non-zero size eliminated
+   with -Wformat-truncation=2
+   { dg-do compile }
+   { dg-options "-O2 -Wall -Wformat-truncation=2 -fprintf-return-value -fdump-tree-optimized" } */
+
+char d[2];
+
+int test_cst (unsigned n)
+{
+  if (1 < n)
+    n = 0;
+
+  return __builtin_snprintf (d, n, "%d", 1);
+}
+
+int test_var (char *d, unsigned n)
+{
+  if (2 < n)
+    n = 0;
+
+  return __builtin_snprintf (d, n, "%i", 1);
+}
+
+/* { dg-final { scan-tree-dump-times "snprintf" 2 "optimized"} } */