On 11/19/2015 05:16 PM, Jason Merrill wrote:
On 11/19/2015 02:44 PM, Martin Sebor wrote:
On 11/18/2015 09:26 PM, Jason Merrill wrote:
The rs6000 target was hitting a bootstrap failure due to
-Werror=type-limits. Since warn_tautological_cmp and other warnings
avoid warning if one of the operands comes from a macro, I thought it
would make sense to do that here as well.
The also disables the warning for functions that are shadowed by
macros such as C atomic_load et al. For example, in the program
below. Is that an acceptable compromise or is there a way to avoid
this?
I think it's an acceptable compromise, but see below.
At the same time, the change doesn't suppress the warning in other
cases where I would have expected it to suppress it based on your
description. For instance here:
unsigned short bar (unsigned short x)
{
#define X x
if (x > 0xffff)
Yes, this is missed because the front end doesn't remember the location
of the use of x; that's one of many location tracking issues. David
Malcolm is working on this stuff.
I noticed there is code elsewhere in c-common.c that avoids
issuing the same warning for system headers (that's the code
that responsible for issuing the warning for the second test
case above).
Hmm, it looks like using expansion_point_if_in_system_header might avoid
the first issue you mention.
Thus.
commit fb71bf4de520cc4bd11eefb57e50748b4679996f
Author: Jason Merrill <ja...@redhat.com>
Date: Thu Nov 19 15:21:47 2015 -0500
* c-common.c (shorten_compare): But look through macros from
system headers.
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 068a0bc..fe0a235 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -4651,8 +4651,10 @@ shorten_compare (location_t loc, tree *op0_ptr, tree *op1_ptr,
}
if (TREE_CODE (primop0) != INTEGER_CST
- /* Don't warn if it's from a macro. */
- && !from_macro_expansion_at (EXPR_LOCATION (primop0)))
+ /* Don't warn if it's from a (non-system) macro. */
+ && !(from_macro_expansion_at
+ (expansion_point_location_if_in_system_header
+ (EXPR_LOCATION (primop0)))))
{
if (val == truthvalue_false_node)
warning_at (loc, OPT_Wtype_limits,
diff --git a/gcc/testsuite/gcc.dg/Wtype-limits2.c b/gcc/testsuite/gcc.dg/Wtype-limits2.c
new file mode 100644
index 0000000..92151aa
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wtype-limits2.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-Wtype-limits" } */
+/* { dg-require-effective-target sync_char_short } */
+
+#include <stdatomic.h>
+
+unsigned foo (unsigned char *x)
+{
+ if (atomic_load (x) > 1000) /* { dg-warning "comparison is always false due to limited range of data type" } */
+ return 0;
+ return 1;
+}
