Re: C++ PATCH to abate shift warnings (PR c++/68979)

[Marek Polacek <polacek@redhat.com>]

On Tue, Jan 12, 2016 at 02:02:16PM +0100, Jakub Jelinek wrote:
> On Tue, Jan 12, 2016 at 01:52:01PM +0100, Marek Polacek wrote:
> > --- gcc/testsuite/g++.dg/warn/permissive-1.C
> > +++ gcc/testsuite/g++.dg/warn/permissive-1.C
> > @@ -0,0 +1,8 @@
> > +// PR c++/68979
> > +// { dg-do compile }
> > +// { dg-options "-fpermissive -Wno-shift-overflow -Wno-shift-count-overflow -Wno-shift-count-negative" }
> > +
> > +enum A { AA = -1 << 4 }; // { dg-warning "operand of shift expression" "" { target c++11 } }
> > +enum B { BB = 1 << -4 }; // { dg-warning "operand of shift expression" }
> > +enum C { CC = 1 << 100 }; // { dg-warning "operand of shift expression" }
> > +enum D { DD = 31 << 30 }; // { dg-warning "shift expression" "" { target c++11 } }
> 
> Shouldn't this test be limited to
> // { dg-do compile { target int32 } }
> or better yet replace the 100 and 30 above with
> say __SIZEOF_INT__ * 4 * __CHAR_BIT__ - 4 and __SIZEOF_INT__ * __CHAR_BIT__ - 2
> ?
> I'd guess that on say int16 targets, or int64 targets (if we have any at
> some point) or int128 targets this wouldn't do what you are expecting.
> { target int32 } is not exactly right, because it still assumes __CHAR_BIT__ == 8
> and for other char sizes it could fail.

Oh yeah, forgot about those...  The following should be better.
Thanks,

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2016-01-12  Marek Polacek  <polacek@redhat.com>

	PR c++/68979
	* constexpr.c (cxx_eval_check_shift_p): Use permerror rather than
	error_at and return negated flag_permissive.

	* g++.dg/warn/permissive-1.C: New test.

diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c
index e60180e..dbcc242 100644
--- gcc/cp/constexpr.c
+++ gcc/cp/constexpr.c
@@ -1512,17 +1512,17 @@ cxx_eval_check_shift_p (location_t loc, const constexpr_ctx *ctx,
   if (tree_int_cst_sgn (rhs) == -1)
     {
       if (!ctx->quiet)
-	error_at (loc, "right operand of shift expression %q+E is negative",
-		  build2_loc (loc, code, type, lhs, rhs));
-      return true;
+	permerror (loc, "right operand of shift expression %q+E is negative",
+		   build2_loc (loc, code, type, lhs, rhs));
+      return !flag_permissive;
     }
   if (compare_tree_int (rhs, uprec) >= 0)
     {
       if (!ctx->quiet)
-	error_at (loc, "right operand of shift expression %q+E is >= than "
-		  "the precision of the left operand",
-		  build2_loc (loc, code, type, lhs, rhs));
-      return true;
+	permerror (loc, "right operand of shift expression %q+E is >= than "
+		   "the precision of the left operand",
+		   build2_loc (loc, code, type, lhs, rhs));
+      return !flag_permissive;
     }
 
   /* The value of E1 << E2 is E1 left-shifted E2 bit positions; [...]
@@ -1536,9 +1536,10 @@ cxx_eval_check_shift_p (location_t loc, const constexpr_ctx *ctx,
       if (tree_int_cst_sgn (lhs) == -1)
 	{
 	  if (!ctx->quiet)
-	    error_at (loc, "left operand of shift expression %q+E is negative",
-		      build2_loc (loc, code, type, lhs, rhs));
-	  return true;
+	    permerror (loc,
+		       "left operand of shift expression %q+E is negative",
+		       build2_loc (loc, code, type, lhs, rhs));
+	  return !flag_permissive;
 	}
       /* For signed x << y the following:
 	 (unsigned) x >> ((prec (lhs) - 1) - y)
@@ -1555,9 +1556,9 @@ cxx_eval_check_shift_p (location_t loc, const constexpr_ctx *ctx,
       if (tree_int_cst_lt (integer_one_node, t))
 	{
 	  if (!ctx->quiet)
-	    error_at (loc, "shift expression %q+E overflows",
-		      build2_loc (loc, code, type, lhs, rhs));
-	  return true;
+	    permerror (loc, "shift expression %q+E overflows",
+		       build2_loc (loc, code, type, lhs, rhs));
+	  return !flag_permissive;
 	}
     }
   return false;
diff --git gcc/testsuite/g++.dg/warn/permissive-1.C gcc/testsuite/g++.dg/warn/permissive-1.C
index e69de29..bfaca76 100644
--- gcc/testsuite/g++.dg/warn/permissive-1.C
+++ gcc/testsuite/g++.dg/warn/permissive-1.C
@@ -0,0 +1,8 @@
+// PR c++/68979
+// { dg-do compile { target int32 } }
+// { dg-options "-fpermissive -Wno-shift-overflow -Wno-shift-count-overflow -Wno-shift-count-negative" }
+
+enum A { AA = -1 << 4 }; // { dg-warning "operand of shift expression" "" { target c++11 } }
+enum B { BB = 1 << -4 }; // { dg-warning "operand of shift expression" }
+enum C { CC = 1 << __SIZEOF_INT__ * 4 * __CHAR_BIT__ - 4 }; // { dg-warning "operand of shift expression" }
+enum D { DD = 10 << __SIZEOF_INT__ * __CHAR_BIT__ - 2 }; // { dg-warning "shift expression" "" { target c++11 } }

	Marek